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From the Archives of the AFIP

Imaging of Musculoskeletal Liposarcoma with Radiologic-Pathologic Correlation¹

¹ From the Departments of Radiologic Pathology (M.D.M., L.K.A.) and Soft Tissue Pathology (J.F.S.), Armed Forces Institute of Pathology, 6825 16th St NW, Bldg 54, Rm M-133A, Washington, DC 20306; Department of Radiology, University of Maryland School of Medicine, Baltimore (M.D.M.); and Department of Radiology, Walter Reed Army Medical Center, Washington, DC (M.D.M.). Received April 29, 2005; revision requested May 26 and received June 20; accepted June 21. All authors have no financial relationships to disclose. Address correspondence to M.D.M. (e-mail: murphey{at}afip.osd.mil).

	Abstract

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Liposarcoma is the second most common type of soft-tissue sarcoma, accounting for 10%–35% of these lesions. The World Health Organization has categorized soft-tissue liposarcomas into five distinct histologic subtypes: well differentiated, dedifferentiated, myxoid, pleomorphic, and mixed type. Well-differentiated liposarcomas frequently demonstrate a diagnostic appearance on computed tomographic (CT) or magnetic resonance (MR) images, with a largely lipomatous mass (>75% of the lesion) and nonlipomatous components in thick septa or focal nodules. The CT or MR imaging finding of a nodular dominant focus (>1 cm in size) of nonlipomatous tissue in a well-differentiated liposarcoma suggests dedifferentiated liposarcoma, and biopsy should be directed at the nonadipose component. The high water content of myxoid liposarcoma seen at pathologic analysis and constituting the majority of the lesion is reflected at sonography, CT, and MR imaging. However, the detection of a small amount of adipose tissue in the septa or as small nodular foci superimposed on the background of myxoid tissue allows prospective diagnosis in 78%–95% of myxoid liposarcomas. Pleomorphic liposarcomas are high-grade sarcomatous lesions and typically appear as heterogeneous soft-tissue masses, although small amounts of fat are seen on MR images in 62%–75% of cases, findings that suggest the diagnosis. Mixed-type liposarcomas have features representing a combination of the other subtypes. Primary liposarcoma of bone is exceedingly rare and usually demonstrates aggressive nonspecific features, although fat may be seen. Understanding and recognition of the spectrum of appearances of the various types of musculoskeletal liposarcoma, which reflect their underlying pathologic characteristics, improves radiologic assessment and is vital for optimal patient management.

	LEARNING OBJECTIVES FOR TEST 6

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
After reading this article and taking the test, the reader will be able to:

• Describe the radiologic spectrum of musculoskeletal liposarcoma.
  
• Recognize the pathologic basis of the radiologic features of liposarcoma involving the musculoskeletal system.
  
• Discuss the radiologic manifestations that may allow differentiation of the various types of liposarcomas involving the musculoskeletal system and their implications on diagnosis, treatment, and prognosis.
  

	Introduction

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Liposarcoma represents the second most common type of soft-tissue sarcoma, exceeded only by fibrous and fibrohistocytic malignancies. Liposarcoma accounts for 10%–35% of all soft-tissue sarcomas, and it has an estimated prevalence of 2.5 cases per million in a Swedish population (1–10). The World Health Organization (WHO) Committee for the Classification of Soft Tissue Tumors in 2002 categorized soft-tissue liposarcomas into five types including well differentiated, dedifferentiated, myxoid, pleomorphic, and mixed (2,4). Enzinger and Winslow (11) emphasized the striking diversity of soft-tissue liposarcomas in their landmark article that reviewed 103 cases. No other mesenchymal tumor shares this wide spectrum of pathologic appearances. The diversity of these lesions is also reflected in their clinical and biologic behavior, which ranges from nonmetastasizing (well-differentiated liposarcoma) to high-grade neoplasms (pleomorphic liposarcoma) with extensive metastatic potential. Primary liposarcoma of bone is an exceedingly rare neoplasm, with a prevalence of 0.03%.

Because of these variations in biologic behavior, pathologic and radiologic assessment is vital to direct appropriate therapy. Imaging findings of liposarcoma are frequently characteristic. Focal or diffuse areas of fat associated with nonlipomatous components are commonly detected on computed tomographic (CT) or magnetic resonance (MR) images. The appearance and morphologic relationship between these areas frequently allow identification of the specific histologic subtype of liposarcoma. In this article, the clinical characteristics, pathologic features, spectrum of radiologic appearances, and the treatment and prognosis of the various types of soft-tissue liposarcoma and primary liposarcoma of bone are discussed and illustrated.

	Well-differentiated Liposarcoma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Clinical Features
Well-differentiated liposarcoma represents the most common type of soft-tissue liposarcoma, accounting for approximately 50% of all liposarcomas (2–4,7,8,10,11). Overall, there is an equal sex distribution, although inguinal lesions are more frequent in men. This lesion occurs almost exclusively in adults, with the peak prevalence in the 6th to 7th decades of life.

Well-differentiated liposarcoma most frequently affects the deep soft tissues of the extremities (65%–75% of cases) (2–4,7,8,10–12) (Figs 1–3). Approximately 51% of all these lesions occur in the lower extremity, particularly the thigh (2–4,7,8,10–12). The retroperitoneum is the second most common location (20%–33% of cases), followed by the upper extremity (14%) (2–4,7,8,10–12) (Fig 4 ). Less frequent locations for well-differentiated liposarcoma include the head and neck (5% of cases) and trunk (12%) (3,8,9). Lesions are most commonly intramuscular (Figs 1, 2), but they also may arise in an inter-muscular or subcutaneous location (Fig 3) (3,8,9).

View larger version (69K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.  Well-differentiated liposarcoma in a 68-year-old man who presented with a slowly enlarging, painless thigh mass. (a) Anteroposterior radiograph shows a mildly heterogeneous mass with radiolucent fat (*). (b) CT scan reveals a heterogeneous, posterior compartment, intramuscular mass composed predominantly of fat (*), with thick septa (arrows) and a nodular focus (arrowhead) of soft-tissue attenuation. (c) Axial T1-weighted (repetition time msec/echo time msec = 400/14) MR image shows the predominant signal intensity of fat (*) with thick septa (arrows) and a nodular nonlipomatous focus of intermediate signal intensity (arrowhead). (d, e) Axial (d) and coronal (e) contrast material–enhanced, fat-suppressed, T1-weighted MR images (683/14) demonstrate enhancement of the septa (arrows) and focal nonlipomatous nodular region (arrowhead) with suppression of the predominant adipose component (*). (f) Axial T2-weighted (5000/96) MR image shows high signal intensity in the septa (arrows) and nodular nonlipomatous focus (arrowhead), with other areas being isointense relative to subcutaneous fat. (g) Photograph of the axially sectioned gross specimen reveals the predominant yellow to tan adipose mass (*) with thick septa (arrows) and a nodular hemorrhagic component (arrowhead) that correspond to imaging findings. The nodular focus requires biopsy to exclude a region of dedifferentiation, which was not seen histologically in this case.

View larger version (60K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.  Well-differentiated liposarcoma in a 68-year-old man who presented with a slowly enlarging, painless thigh mass. (a) Anteroposterior radiograph shows a mildly heterogeneous mass with radiolucent fat (*). (b) CT scan reveals a heterogeneous, posterior compartment, intramuscular mass composed predominantly of fat (*), with thick septa (arrows) and a nodular focus (arrowhead) of soft-tissue attenuation. (c) Axial T1-weighted (repetition time msec/echo time msec = 400/14) MR image shows the predominant signal intensity of fat (*) with thick septa (arrows) and a nodular nonlipomatous focus of intermediate signal intensity (arrowhead). (d, e) Axial (d) and coronal (e) contrast material–enhanced, fat-suppressed, T1-weighted MR images (683/14) demonstrate enhancement of the septa (arrows) and focal nonlipomatous nodular region (arrowhead) with suppression of the predominant adipose component (*). (f) Axial T2-weighted (5000/96) MR image shows high signal intensity in the septa (arrows) and nodular nonlipomatous focus (arrowhead), with other areas being isointense relative to subcutaneous fat. (g) Photograph of the axially sectioned gross specimen reveals the predominant yellow to tan adipose mass (*) with thick septa (arrows) and a nodular hemorrhagic component (arrowhead) that correspond to imaging findings. The nodular focus requires biopsy to exclude a region of dedifferentiation, which was not seen histologically in this case.

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 1c.  Well-differentiated liposarcoma in a 68-year-old man who presented with a slowly enlarging, painless thigh mass. (a) Anteroposterior radiograph shows a mildly heterogeneous mass with radiolucent fat (*). (b) CT scan reveals a heterogeneous, posterior compartment, intramuscular mass composed predominantly of fat (*), with thick septa (arrows) and a nodular focus (arrowhead) of soft-tissue attenuation. (c) Axial T1-weighted (repetition time msec/echo time msec = 400/14) MR image shows the predominant signal intensity of fat (*) with thick septa (arrows) and a nodular nonlipomatous focus of intermediate signal intensity (arrowhead). (d, e) Axial (d) and coronal (e) contrast material–enhanced, fat-suppressed, T1-weighted MR images (683/14) demonstrate enhancement of the septa (arrows) and focal nonlipomatous nodular region (arrowhead) with suppression of the predominant adipose component (*). (f) Axial T2-weighted (5000/96) MR image shows high signal intensity in the septa (arrows) and nodular nonlipomatous focus (arrowhead), with other areas being isointense relative to subcutaneous fat. (g) Photograph of the axially sectioned gross specimen reveals the predominant yellow to tan adipose mass (*) with thick septa (arrows) and a nodular hemorrhagic component (arrowhead) that correspond to imaging findings. The nodular focus requires biopsy to exclude a region of dedifferentiation, which was not seen histologically in this case.

View larger version (90K): [in this window] [in a new window] [Download PPT slide]   Figure 1d.  Well-differentiated liposarcoma in a 68-year-old man who presented with a slowly enlarging, painless thigh mass. (a) Anteroposterior radiograph shows a mildly heterogeneous mass with radiolucent fat (*). (b) CT scan reveals a heterogeneous, posterior compartment, intramuscular mass composed predominantly of fat (*), with thick septa (arrows) and a nodular focus (arrowhead) of soft-tissue attenuation. (c) Axial T1-weighted (repetition time msec/echo time msec = 400/14) MR image shows the predominant signal intensity of fat (*) with thick septa (arrows) and a nodular nonlipomatous focus of intermediate signal intensity (arrowhead). (d, e) Axial (d) and coronal (e) contrast material–enhanced, fat-suppressed, T1-weighted MR images (683/14) demonstrate enhancement of the septa (arrows) and focal nonlipomatous nodular region (arrowhead) with suppression of the predominant adipose component (*). (f) Axial T2-weighted (5000/96) MR image shows high signal intensity in the septa (arrows) and nodular nonlipomatous focus (arrowhead), with other areas being isointense relative to subcutaneous fat. (g) Photograph of the axially sectioned gross specimen reveals the predominant yellow to tan adipose mass (*) with thick septa (arrows) and a nodular hemorrhagic component (arrowhead) that correspond to imaging findings. The nodular focus requires biopsy to exclude a region of dedifferentiation, which was not seen histologically in this case.

View larger version (98K): [in this window] [in a new window] [Download PPT slide]   Figure 1e.  Well-differentiated liposarcoma in a 68-year-old man who presented with a slowly enlarging, painless thigh mass. (a) Anteroposterior radiograph shows a mildly heterogeneous mass with radiolucent fat (*). (b) CT scan reveals a heterogeneous, posterior compartment, intramuscular mass composed predominantly of fat (*), with thick septa (arrows) and a nodular focus (arrowhead) of soft-tissue attenuation. (c) Axial T1-weighted (repetition time msec/echo time msec = 400/14) MR image shows the predominant signal intensity of fat (*) with thick septa (arrows) and a nodular nonlipomatous focus of intermediate signal intensity (arrowhead). (d, e) Axial (d) and coronal (e) contrast material–enhanced, fat-suppressed, T1-weighted MR images (683/14) demonstrate enhancement of the septa (arrows) and focal nonlipomatous nodular region (arrowhead) with suppression of the predominant adipose component (*). (f) Axial T2-weighted (5000/96) MR image shows high signal intensity in the septa (arrows) and nodular nonlipomatous focus (arrowhead), with other areas being isointense relative to subcutaneous fat. (g) Photograph of the axially sectioned gross specimen reveals the predominant yellow to tan adipose mass (*) with thick septa (arrows) and a nodular hemorrhagic component (arrowhead) that correspond to imaging findings. The nodular focus requires biopsy to exclude a region of dedifferentiation, which was not seen histologically in this case.

View larger version (91K): [in this window] [in a new window] [Download PPT slide]   Figure 1f.  Well-differentiated liposarcoma in a 68-year-old man who presented with a slowly enlarging, painless thigh mass. (a) Anteroposterior radiograph shows a mildly heterogeneous mass with radiolucent fat (*). (b) CT scan reveals a heterogeneous, posterior compartment, intramuscular mass composed predominantly of fat (*), with thick septa (arrows) and a nodular focus (arrowhead) of soft-tissue attenuation. (c) Axial T1-weighted (repetition time msec/echo time msec = 400/14) MR image shows the predominant signal intensity of fat (*) with thick septa (arrows) and a nodular nonlipomatous focus of intermediate signal intensity (arrowhead). (d, e) Axial (d) and coronal (e) contrast material–enhanced, fat-suppressed, T1-weighted MR images (683/14) demonstrate enhancement of the septa (arrows) and focal nonlipomatous nodular region (arrowhead) with suppression of the predominant adipose component (*). (f) Axial T2-weighted (5000/96) MR image shows high signal intensity in the septa (arrows) and nodular nonlipomatous focus (arrowhead), with other areas being isointense relative to subcutaneous fat. (g) Photograph of the axially sectioned gross specimen reveals the predominant yellow to tan adipose mass (*) with thick septa (arrows) and a nodular hemorrhagic component (arrowhead) that correspond to imaging findings. The nodular focus requires biopsy to exclude a region of dedifferentiation, which was not seen histologically in this case.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 1g.  Well-differentiated liposarcoma in a 68-year-old man who presented with a slowly enlarging, painless thigh mass. (a) Anteroposterior radiograph shows a mildly heterogeneous mass with radiolucent fat (*). (b) CT scan reveals a heterogeneous, posterior compartment, intramuscular mass composed predominantly of fat (*), with thick septa (arrows) and a nodular focus (arrowhead) of soft-tissue attenuation. (c) Axial T1-weighted (repetition time msec/echo time msec = 400/14) MR image shows the predominant signal intensity of fat (*) with thick septa (arrows) and a nodular nonlipomatous focus of intermediate signal intensity (arrowhead). (d, e) Axial (d) and coronal (e) contrast material–enhanced, fat-suppressed, T1-weighted MR images (683/14) demonstrate enhancement of the septa (arrows) and focal nonlipomatous nodular region (arrowhead) with suppression of the predominant adipose component (*). (f) Axial T2-weighted (5000/96) MR image shows high signal intensity in the septa (arrows) and nodular nonlipomatous focus (arrowhead), with other areas being isointense relative to subcutaneous fat. (g) Photograph of the axially sectioned gross specimen reveals the predominant yellow to tan adipose mass (*) with thick septa (arrows) and a nodular hemorrhagic component (arrowhead) that correspond to imaging findings. The nodular focus requires biopsy to exclude a region of dedifferentiation, which was not seen histologically in this case.

View larger version (128K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Well-differentiated intermuscular liposarcoma of the thigh in a 72-year-old woman with a history of a painless, slow-growing mass. Radiographs (not shown) were unremarkable. (a) CT scan shows an intermuscular mass between the superficial fascia (arrow) and vastus lateralis muscle (VL) that is predominantly composed of fat attenuation (*) with prominent thick and nodular septa (arrowheads). (b–d) Axial T1-weighted (500/13) (b), contrast-enhanced T1-weighted fat-suppressed (523/13) (c), and T2-weighted (2300/15) (d) MR images also reveal a lipomatous mass (*) with prominent septa (arrows) and enhancement. (e) Photograph of the excised specimen demonstrates the predominantly yellow lipomatous mass (*) with thick septa (arrows). (f) Photomicrograph (original magnification, x 175; hematoxylin-eosin stain) shows the adipose tissue (*) and thick septa (S).

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Well-differentiated intermuscular liposarcoma of the thigh in a 72-year-old woman with a history of a painless, slow-growing mass. Radiographs (not shown) were unremarkable. (a) CT scan shows an intermuscular mass between the superficial fascia (arrow) and vastus lateralis muscle (VL) that is predominantly composed of fat attenuation (*) with prominent thick and nodular septa (arrowheads). (b–d) Axial T1-weighted (500/13) (b), contrast-enhanced T1-weighted fat-suppressed (523/13) (c), and T2-weighted (2300/15) (d) MR images also reveal a lipomatous mass (*) with prominent septa (arrows) and enhancement. (e) Photograph of the excised specimen demonstrates the predominantly yellow lipomatous mass (*) with thick septa (arrows). (f) Photomicrograph (original magnification, x 175; hematoxylin-eosin stain) shows the adipose tissue (*) and thick septa (S).

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 2c.  Well-differentiated intermuscular liposarcoma of the thigh in a 72-year-old woman with a history of a painless, slow-growing mass. Radiographs (not shown) were unremarkable. (a) CT scan shows an intermuscular mass between the superficial fascia (arrow) and vastus lateralis muscle (VL) that is predominantly composed of fat attenuation (*) with prominent thick and nodular septa (arrowheads). (b–d) Axial T1-weighted (500/13) (b), contrast-enhanced T1-weighted fat-suppressed (523/13) (c), and T2-weighted (2300/15) (d) MR images also reveal a lipomatous mass (*) with prominent septa (arrows) and enhancement. (e) Photograph of the excised specimen demonstrates the predominantly yellow lipomatous mass (*) with thick septa (arrows). (f) Photomicrograph (original magnification, x 175; hematoxylin-eosin stain) shows the adipose tissue (*) and thick septa (S).

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 2d.  Well-differentiated intermuscular liposarcoma of the thigh in a 72-year-old woman with a history of a painless, slow-growing mass. Radiographs (not shown) were unremarkable. (a) CT scan shows an intermuscular mass between the superficial fascia (arrow) and vastus lateralis muscle (VL) that is predominantly composed of fat attenuation (*) with prominent thick and nodular septa (arrowheads). (b–d) Axial T1-weighted (500/13) (b), contrast-enhanced T1-weighted fat-suppressed (523/13) (c), and T2-weighted (2300/15) (d) MR images also reveal a lipomatous mass (*) with prominent septa (arrows) and enhancement. (e) Photograph of the excised specimen demonstrates the predominantly yellow lipomatous mass (*) with thick septa (arrows). (f) Photomicrograph (original magnification, x 175; hematoxylin-eosin stain) shows the adipose tissue (*) and thick septa (S).

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 2e.  Well-differentiated intermuscular liposarcoma of the thigh in a 72-year-old woman with a history of a painless, slow-growing mass. Radiographs (not shown) were unremarkable. (a) CT scan shows an intermuscular mass between the superficial fascia (arrow) and vastus lateralis muscle (VL) that is predominantly composed of fat attenuation (*) with prominent thick and nodular septa (arrowheads). (b–d) Axial T1-weighted (500/13) (b), contrast-enhanced T1-weighted fat-suppressed (523/13) (c), and T2-weighted (2300/15) (d) MR images also reveal a lipomatous mass (*) with prominent septa (arrows) and enhancement. (e) Photograph of the excised specimen demonstrates the predominantly yellow lipomatous mass (*) with thick septa (arrows). (f) Photomicrograph (original magnification, x 175; hematoxylin-eosin stain) shows the adipose tissue (*) and thick septa (S).

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 2f.  Well-differentiated intermuscular liposarcoma of the thigh in a 72-year-old woman with a history of a painless, slow-growing mass. Radiographs (not shown) were unremarkable. (a) CT scan shows an intermuscular mass between the superficial fascia (arrow) and vastus lateralis muscle (VL) that is predominantly composed of fat attenuation (*) with prominent thick and nodular septa (arrowheads). (b–d) Axial T1-weighted (500/13) (b), contrast-enhanced T1-weighted fat-suppressed (523/13) (c), and T2-weighted (2300/15) (d) MR images also reveal a lipomatous mass (*) with prominent septa (arrows) and enhancement. (e) Photograph of the excised specimen demonstrates the predominantly yellow lipomatous mass (*) with thick septa (arrows). (f) Photomicrograph (original magnification, x 175; hematoxylin-eosin stain) shows the adipose tissue (*) and thick septa (S).

View larger version (79K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.  Well-differentiated liposarcoma of the thigh in a 65-year-old woman with a 3-year history of a slowly growing, painless mass. (a) Lateral radiograph of the thigh shows a large mass with prominent radiolucent fat (*). (b) CT scan reveals the low-attenuation fat (*) with numerous thick (>2 mm) septa (arrows) and encasement of the neurovascular bundle (arrowhead). (c, d) Axial (700/14) (c) and sagittal (650/14) (d) T1-weighted MR images demonstrate a high-signal-intensity adipose lesion that involves both intramuscular and intermuscular portions of the posterior thigh compartment (*) and that contains thick septa (solid arrows) and several areas of mild nodularity (arrowheads). The axial image also reveals encasement of the neurovascular bundle (open arrow). (e) Sagittal T2-weighted (2100/90) MR image shows that the tissue is isointense relative to subcutaneous fat (*); the thick septa reveal both high and low signal intensity (arrows). (f) Intraoperative photograph demonstrates the large lipomatous mass (L) and mobilization of the neurovascular bundle (N). (g) Photograph of the sectioned gross specimen shows the yellow lipomatous tissue (L) and multiple septa (arrows).

View larger version (161K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.  Well-differentiated liposarcoma of the thigh in a 65-year-old woman with a 3-year history of a slowly growing, painless mass. (a) Lateral radiograph of the thigh shows a large mass with prominent radiolucent fat (*). (b) CT scan reveals the low-attenuation fat (*) with numerous thick (>2 mm) septa (arrows) and encasement of the neurovascular bundle (arrowhead). (c, d) Axial (700/14) (c) and sagittal (650/14) (d) T1-weighted MR images demonstrate a high-signal-intensity adipose lesion that involves both intramuscular and intermuscular portions of the posterior thigh compartment (*) and that contains thick septa (solid arrows) and several areas of mild nodularity (arrowheads). The axial image also reveals encasement of the neurovascular bundle (open arrow). (e) Sagittal T2-weighted (2100/90) MR image shows that the tissue is isointense relative to subcutaneous fat (*); the thick septa reveal both high and low signal intensity (arrows). (f) Intraoperative photograph demonstrates the large lipomatous mass (L) and mobilization of the neurovascular bundle (N). (g) Photograph of the sectioned gross specimen shows the yellow lipomatous tissue (L) and multiple septa (arrows).

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.  Well-differentiated liposarcoma of the thigh in a 65-year-old woman with a 3-year history of a slowly growing, painless mass. (a) Lateral radiograph of the thigh shows a large mass with prominent radiolucent fat (*). (b) CT scan reveals the low-attenuation fat (*) with numerous thick (>2 mm) septa (arrows) and encasement of the neurovascular bundle (arrowhead). (c, d) Axial (700/14) (c) and sagittal (650/14) (d) T1-weighted MR images demonstrate a high-signal-intensity adipose lesion that involves both intramuscular and intermuscular portions of the posterior thigh compartment (*) and that contains thick septa (solid arrows) and several areas of mild nodularity (arrowheads). The axial image also reveals encasement of the neurovascular bundle (open arrow). (e) Sagittal T2-weighted (2100/90) MR image shows that the tissue is isointense relative to subcutaneous fat (*); the thick septa reveal both high and low signal intensity (arrows). (f) Intraoperative photograph demonstrates the large lipomatous mass (L) and mobilization of the neurovascular bundle (N). (g) Photograph of the sectioned gross specimen shows the yellow lipomatous tissue (L) and multiple septa (arrows).

View larger version (106K): [in this window] [in a new window] [Download PPT slide]   Figure 3d.  Well-differentiated liposarcoma of the thigh in a 65-year-old woman with a 3-year history of a slowly growing, painless mass. (a) Lateral radiograph of the thigh shows a large mass with prominent radiolucent fat (*). (b) CT scan reveals the low-attenuation fat (*) with numerous thick (>2 mm) septa (arrows) and encasement of the neurovascular bundle (arrowhead). (c, d) Axial (700/14) (c) and sagittal (650/14) (d) T1-weighted MR images demonstrate a high-signal-intensity adipose lesion that involves both intramuscular and intermuscular portions of the posterior thigh compartment (*) and that contains thick septa (solid arrows) and several areas of mild nodularity (arrowheads). The axial image also reveals encasement of the neurovascular bundle (open arrow). (e) Sagittal T2-weighted (2100/90) MR image shows that the tissue is isointense relative to subcutaneous fat (*); the thick septa reveal both high and low signal intensity (arrows). (f) Intraoperative photograph demonstrates the large lipomatous mass (L) and mobilization of the neurovascular bundle (N). (g) Photograph of the sectioned gross specimen shows the yellow lipomatous tissue (L) and multiple septa (arrows).

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 3e.  Well-differentiated liposarcoma of the thigh in a 65-year-old woman with a 3-year history of a slowly growing, painless mass. (a) Lateral radiograph of the thigh shows a large mass with prominent radiolucent fat (*). (b) CT scan reveals the low-attenuation fat (*) with numerous thick (>2 mm) septa (arrows) and encasement of the neurovascular bundle (arrowhead). (c, d) Axial (700/14) (c) and sagittal (650/14) (d) T1-weighted MR images demonstrate a high-signal-intensity adipose lesion that involves both intramuscular and intermuscular portions of the posterior thigh compartment (*) and that contains thick septa (solid arrows) and several areas of mild nodularity (arrowheads). The axial image also reveals encasement of the neurovascular bundle (open arrow). (e) Sagittal T2-weighted (2100/90) MR image shows that the tissue is isointense relative to subcutaneous fat (*); the thick septa reveal both high and low signal intensity (arrows). (f) Intraoperative photograph demonstrates the large lipomatous mass (L) and mobilization of the neurovascular bundle (N). (g) Photograph of the sectioned gross specimen shows the yellow lipomatous tissue (L) and multiple septa (arrows).

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 3f.  Well-differentiated liposarcoma of the thigh in a 65-year-old woman with a 3-year history of a slowly growing, painless mass. (a) Lateral radiograph of the thigh shows a large mass with prominent radiolucent fat (*). (b) CT scan reveals the low-attenuation fat (*) with numerous thick (>2 mm) septa (arrows) and encasement of the neurovascular bundle (arrowhead). (c, d) Axial (700/14) (c) and sagittal (650/14) (d) T1-weighted MR images demonstrate a high-signal-intensity adipose lesion that involves both intramuscular and intermuscular portions of the posterior thigh compartment (*) and that contains thick septa (solid arrows) and several areas of mild nodularity (arrowheads). The axial image also reveals encasement of the neurovascular bundle (open arrow). (e) Sagittal T2-weighted (2100/90) MR image shows that the tissue is isointense relative to subcutaneous fat (*); the thick septa reveal both high and low signal intensity (arrows). (f) Intraoperative photograph demonstrates the large lipomatous mass (L) and mobilization of the neurovascular bundle (N). (g) Photograph of the sectioned gross specimen shows the yellow lipomatous tissue (L) and multiple septa (arrows).

View larger version (100K): [in this window] [in a new window] [Download PPT slide]   Figure 3g.  Well-differentiated liposarcoma of the thigh in a 65-year-old woman with a 3-year history of a slowly growing, painless mass. (a) Lateral radiograph of the thigh shows a large mass with prominent radiolucent fat (*). (b) CT scan reveals the low-attenuation fat (*) with numerous thick (>2 mm) septa (arrows) and encasement of the neurovascular bundle (arrowhead). (c, d) Axial (700/14) (c) and sagittal (650/14) (d) T1-weighted MR images demonstrate a high-signal-intensity adipose lesion that involves both intramuscular and intermuscular portions of the posterior thigh compartment (*) and that contains thick septa (solid arrows) and several areas of mild nodularity (arrowheads). The axial image also reveals encasement of the neurovascular bundle (open arrow). (e) Sagittal T2-weighted (2100/90) MR image shows that the tissue is isointense relative to subcutaneous fat (*); the thick septa reveal both high and low signal intensity (arrows). (f) Intraoperative photograph demonstrates the large lipomatous mass (L) and mobilization of the neurovascular bundle (N). (g) Photograph of the sectioned gross specimen shows the yellow lipomatous tissue (L) and multiple septa (arrows).

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Subcutaneous atypical lipomatous tumor/well-differentiated liposarcoma in a 55-year-old man who presented with an enlarging, mildly painful mass. (a, b) Coronal T1-weighted (500/20) (a) and axial T2-weighted (2500/90) (b) MR images show a largely lipomatous subcutaneous mass (*) with prominent thick and nodular septa (arrows). (c) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) reveals typical features of a lipoma-like atypical lipomatous tumor/well-differentiated liposarcoma with largely mature adipocytes (A), only mild atypia (arrows), and thick septa (S).

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Subcutaneous atypical lipomatous tumor/well-differentiated liposarcoma in a 55-year-old man who presented with an enlarging, mildly painful mass. (a, b) Coronal T1-weighted (500/20) (a) and axial T2-weighted (2500/90) (b) MR images show a largely lipomatous subcutaneous mass (*) with prominent thick and nodular septa (arrows). (c) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) reveals typical features of a lipoma-like atypical lipomatous tumor/well-differentiated liposarcoma with largely mature adipocytes (A), only mild atypia (arrows), and thick septa (S).

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.  Subcutaneous atypical lipomatous tumor/well-differentiated liposarcoma in a 55-year-old man who presented with an enlarging, mildly painful mass. (a, b) Coronal T1-weighted (500/20) (a) and axial T2-weighted (2500/90) (b) MR images show a largely lipomatous subcutaneous mass (*) with prominent thick and nodular septa (arrows). (c) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) reveals typical features of a lipoma-like atypical lipomatous tumor/well-differentiated liposarcoma with largely mature adipocytes (A), only mild atypia (arrows), and thick septa (S).

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  Retroperitoneal well-differentiated liposarcoma in a 60-year-old man with a history of increasing abdominal girth. (a) CT scan shows a large retroperitoneal and abdominal mass composed of fat (F) with Hounsfield (HU) measurements of –80 to –120. There are multiple thick septa (arrowheads) and a posterior component (*) with mildly higher attenuation (320 to 335 HU). (b, c) Photographs of the gross specimen (b) and axially sectioned specimen (c) reveal that the large mass is predominantly composed of fat (*) with some heterogeneous intermixed myxoid areas (m) that correspond to the imaging findings.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  Retroperitoneal well-differentiated liposarcoma in a 60-year-old man with a history of increasing abdominal girth. (a) CT scan shows a large retroperitoneal and abdominal mass composed of fat (F) with Hounsfield (HU) measurements of –80 to –120. There are multiple thick septa (arrowheads) and a posterior component (*) with mildly higher attenuation (320 to 335 HU). (b, c) Photographs of the gross specimen (b) and axially sectioned specimen (c) reveal that the large mass is predominantly composed of fat (*) with some heterogeneous intermixed myxoid areas (m) that correspond to the imaging findings.

View larger version (102K): [in this window] [in a new window] [Download PPT slide]   Figure 5c.  Retroperitoneal well-differentiated liposarcoma in a 60-year-old man with a history of increasing abdominal girth. (a) CT scan shows a large retroperitoneal and abdominal mass composed of fat (F) with Hounsfield (HU) measurements of –80 to –120. There are multiple thick septa (arrowheads) and a posterior component (*) with mildly higher attenuation (320 to 335 HU). (b, c) Photographs of the gross specimen (b) and axially sectioned specimen (c) reveal that the large mass is predominantly composed of fat (*) with some heterogeneous intermixed myxoid areas (m) that correspond to the imaging findings.

Pathologic Features
The gross pathologic appearance of well-differentiated liposarcoma is that of a large, multilobulated, well-circumscribed mass ranging from yellow to white (Figs 1–3, 5). Well-differentiated liposarcoma is a low-grade neoplasm with five histologic variants: lipoma-like, sclerosing, inflammatory, spindle cell, and liposarcoma with meningothelial whorls (which may indicate early dedifferentiation) (2,17–24). Only the first two types—lipoma-like and sclerosing—are common, and many pathologists do not routinely subclassify these lesions. We describe only the first three types herein.

The lipoma-like well-differentiated liposarcoma is the most common variant. Some sections of the tumor are composed of abundant mature adipose tissue that can appear identical to classic lipoma (6–10). However, other regions are focally punctuated by scattered lipoblasts or cells with enlarged hyperchromatic nuclei representing lipocytic atypia, and this latter finding is required for diagnosis (Fig 4). There is expansion of the fibrous interlobular septa with increased cellularity or hyperchromatism. Variable degrees of myxoid change and fat necrosis may also be seen. Metaplastic bone or cartilage may also be found in this type of well-differentiated liposarcoma (6,7,9,10).

The sclerosing type of well-differentiated liposarcoma has broad bands and patches of a collagen fiber meshwork that harbor the atypical cells and surround groups of adipocytes or single cells. The cellularity is variable. When the lesions have alipogenic areas that constitute more than a 10X power field, they are classified as dedifferentiated, even if they are low or intermediate grade. In fact, many lesions previously considered sclerosing liposarcomas are now classified as dedifferentiated liposarcomas.

The inflammatory type of well-differentiated liposarcoma occurs almost exclusively in the retroperitoneum. It consists of a lipoma-like or sclerosing lesion with superimposed, dense lymphocytic or plasmacytic infiltrate. Many pathologists no longer use this term, since it is not uncommon for liposarcomas to have some associated inflammatory component.

All subtypes of well-differentiated liposarcomas are genetically characterized by supernumerary circular (ring) and giant rod chromosomes (25–29). In one study, clonal abnormalities were seen in 93% of cases, with 63% revealing the ring or giant marker chromosomes (30,31). These chromosomal abnormalities contain amplification of the 12q13–15 region. Lipomas do not contain this genetic marker, which is further evidence that well-differentiated liposarcomas are distinct lesions.

Imaging Features
At radiography, well-differentiated liposarcoma may appear as a soft-tissue mass, depending on the size and location of the lesion. Fat is frequently seen in large masses affecting the extremities (Figs 1, 3) but is very rarely detected in a retroperitoneal lesions. Calcification or metaplastic ossification has been reported in 10%–32% of lesions (as seen either with radiography or CT) (12,24,32,33) (Fig 6). Secondary osseous involvement by soft-tissue liposarcomas of any histologic type is exceedingly rare.

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.  Dedifferentiated liposarcoma of the thigh in a 72-year-old man with a 10-year history of a slowly enlarging mass with recent rapid growth. (a) Anteroposterior radiograph of the thigh shows a large mass with calcified areas (C), radiolucent adipose regions (A), and a superior soft-tissue component (S) that correspond to the recent area of rapid growth. (b, c) Sagittal T1-weighted (500/16) (b) and T2-weighted (1600/120) (c) MR images reveal that the mass is composed largely of tissue isointense relative to subcutaneous fat (*) but also contains thick septa (arrows). There is also a large nodular, nonlipomatous component (O) with nonspecific characteristics of low signal intensity with T1-weighting and heterogeneous intermediate to high signal intensity with T2-weighting. (d) Photograph of the resected gross specimen shows a lipomatous mass (L) with a nodular hemorrhagic component (H). (e) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) reveals well-differentiated liposarcoma (L) and a high-grade dedifferentiated spindle cell component (M) (malignant fibrous histiocytoma-like), findings that correspond to the imaging appearances. The calcified area (not shown) represented metaplastic ossification in the well-differentiated liposarcoma.

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.  Dedifferentiated liposarcoma of the thigh in a 72-year-old man with a 10-year history of a slowly enlarging mass with recent rapid growth. (a) Anteroposterior radiograph of the thigh shows a large mass with calcified areas (C), radiolucent adipose regions (A), and a superior soft-tissue component (S) that correspond to the recent area of rapid growth. (b, c) Sagittal T1-weighted (500/16) (b) and T2-weighted (1600/120) (c) MR images reveal that the mass is composed largely of tissue isointense relative to subcutaneous fat (*) but also contains thick septa (arrows). There is also a large nodular, nonlipomatous component (O) with nonspecific characteristics of low signal intensity with T1-weighting and heterogeneous intermediate to high signal intensity with T2-weighting. (d) Photograph of the resected gross specimen shows a lipomatous mass (L) with a nodular hemorrhagic component (H). (e) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) reveals well-differentiated liposarcoma (L) and a high-grade dedifferentiated spindle cell component (M) (malignant fibrous histiocytoma-like), findings that correspond to the imaging appearances. The calcified area (not shown) represented metaplastic ossification in the well-differentiated liposarcoma.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 6c.  Dedifferentiated liposarcoma of the thigh in a 72-year-old man with a 10-year history of a slowly enlarging mass with recent rapid growth. (a) Anteroposterior radiograph of the thigh shows a large mass with calcified areas (C), radiolucent adipose regions (A), and a superior soft-tissue component (S) that correspond to the recent area of rapid growth. (b, c) Sagittal T1-weighted (500/16) (b) and T2-weighted (1600/120) (c) MR images reveal that the mass is composed largely of tissue isointense relative to subcutaneous fat (*) but also contains thick septa (arrows). There is also a large nodular, nonlipomatous component (O) with nonspecific characteristics of low signal intensity with T1-weighting and heterogeneous intermediate to high signal intensity with T2-weighting. (d) Photograph of the resected gross specimen shows a lipomatous mass (L) with a nodular hemorrhagic component (H). (e) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) reveals well-differentiated liposarcoma (L) and a high-grade dedifferentiated spindle cell component (M) (malignant fibrous histiocytoma-like), findings that correspond to the imaging appearances. The calcified area (not shown) represented metaplastic ossification in the well-differentiated liposarcoma.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 6d.  Dedifferentiated liposarcoma of the thigh in a 72-year-old man with a 10-year history of a slowly enlarging mass with recent rapid growth. (a) Anteroposterior radiograph of the thigh shows a large mass with calcified areas (C), radiolucent adipose regions (A), and a superior soft-tissue component (S) that correspond to the recent area of rapid growth. (b, c) Sagittal T1-weighted (500/16) (b) and T2-weighted (1600/120) (c) MR images reveal that the mass is composed largely of tissue isointense relative to subcutaneous fat (*) but also contains thick septa (arrows). There is also a large nodular, nonlipomatous component (O) with nonspecific characteristics of low signal intensity with T1-weighting and heterogeneous intermediate to high signal intensity with T2-weighting. (d) Photograph of the resected gross specimen shows a lipomatous mass (L) with a nodular hemorrhagic component (H). (e) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) reveals well-differentiated liposarcoma (L) and a high-grade dedifferentiated spindle cell component (M) (malignant fibrous histiocytoma-like), findings that correspond to the imaging appearances. The calcified area (not shown) represented metaplastic ossification in the well-differentiated liposarcoma.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 6e.  Dedifferentiated liposarcoma of the thigh in a 72-year-old man with a 10-year history of a slowly enlarging mass with recent rapid growth. (a) Anteroposterior radiograph of the thigh shows a large mass with calcified areas (C), radiolucent adipose regions (A), and a superior soft-tissue component (S) that correspond to the recent area of rapid growth. (b, c) Sagittal T1-weighted (500/16) (b) and T2-weighted (1600/120) (c) MR images reveal that the mass is composed largely of tissue isointense relative to subcutaneous fat (*) but also contains thick septa (arrows). There is also a large nodular, nonlipomatous component (O) with nonspecific characteristics of low signal intensity with T1-weighting and heterogeneous intermediate to high signal intensity with T2-weighting. (d) Photograph of the resected gross specimen shows a lipomatous mass (L) with a nodular hemorrhagic component (H). (e) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) reveals well-differentiated liposarcoma (L) and a high-grade dedifferentiated spindle cell component (M) (malignant fibrous histiocytoma-like), findings that correspond to the imaging appearances. The calcified area (not shown) represented metaplastic ossification in the well-differentiated liposarcoma.

At CT and MR imaging, well-differentiated liposarcoma typically has a relatively characteristic appearance as a predominantly adipose mass containing nonlipomatous components (Figs 1–5) (12,33,38–46). Generally, greater than 75% of a well-differentiated liposarcoma is composed of fat (Figs 1–5). The nonlipomatous components are most often seen as prominent thick septa (>2 mm) that may show nodularity (Figs 2–4) (12,33,38,40,47). Focal nodular or globular nonadipose areas may also be apparent, but they are usually less than 2 cm in size (Fig 1).

The lesion that is most difficult to distinguish from well-differentiated liposarcoma radiologically is lipoma (46,48). Most lipomas (48%–71%) are entirely composed of homogeneous fat (11%–22% of cases) or are largely adipose with only thin (<2 mm) septa (37%–49%); these lipomas are easily distinguished from well-differentiated liposarcoma (12,33,38,40,46,47). In a study of 60 adipose neoplasms by Kransdorf and colleagues (33), 24 of 25 (96%) lesions with thick (>2 mm) septa and 10 of 12 (83%) lesions with nodular or globular nonlipomatous foci were well-differentiated liposarcomas as opposed to lipoma. However, lipomas can have a more complex appearance (28%–31% of cases) simulating that of well-differentiated liposarcoma from which they cannot be distinguished radiologically (46). Recently, positron emission tomography showed that four of six (67%) well-differentiated liposarcomas had low radionuclide uptake, a finding that reflects the low-grade nature of these lesions and again demonstrates the difficulty of differentiating them from lipoma (49). Statistically significant factors favoring the diagnosis of well-differentiated liposarcoma as opposed to lipoma (associated odds ratio [OR] favoring liposarcoma in parentheses) include male sex (OR = 3), age greater than 66 years (OR = 6), a lower percentage of fat (<75% of the lesion) (OR = 8.3), presence of calcification, lesion size greater than 10 cm (OR = 14.2), thick (>2 mm) septa (OR = 4.9), and nonlipomatous nodular or globular foci (OR = 2.3) (33).

Well-differentiated liposarcomas only rarely demonstrate thin (<2 mm) septa (4%–9% of cases), and these lesions are usually superficial (12,33,38,40,46,47). Gadolinium contrast enhancement patterns and degree may also be helpful in distinguishing well-differentiated liposarcoma from lipoma. Ohguri et al (47) demonstrated in their study that 58% of lipomas showed no enhancement with 37% revealing moderate enhancement of the septa. In contradistinction, well-differentiated liposarcomas revealed moderate (25%) to marked (75%) enhancement of the septa in all cases (47). Hosono and colleagues (40) observed similar findings in their smaller study.

The way we approach the diagnosis of lipomatous masses is to categorize the lesions according to imaging patterns and location. Lipomatous lesions in almost any location with nonfatty components that have either prominent thick (>2 mm) septa or nodular to globular foci are considered well-differentiated liposarcoma, particularly if there is contrast enhancement. In this approach, we acknowledge that a small percentage of these lesions (particularly superficial lesions) will be lipomas pathologically, and we believe this limitation must be accepted. There are exceptions to this rule, such as a lesion in the subcutaneous tissues of the posterior neck, which most likely is a spindle cell lipoma. Lipomatous lesions composed of pure fat or containing thin (<2 mm) septa, particularly without prominent contrast enhancement at MR imaging, are considered lipomas unless they are located in the mediastinum or retroperitoneum (Fig 5). Lipomas are extraordinarily rare in these latter locations, and any largely lipomatous lesion in these areas of an adult is best considered a well-differentiated liposarcoma (Fig 5). It is also important to understand that well-differentiated liposarcomas do not arise from lipomas. Malignant transformation of lipoma has only rarely been reported (50–52). In fact, we believe that malignant transformation is nonexistent and that reported cases likely represent sampling errors or misdiagnosis at initial evaluation.

Treatment and Prognosis
Well-differentiated liposarcoma has no metastatic potential unless dedifferentiation occurs, but lesions may locally recur. The prognosis and treatment of well-differentiated liposarcomas are therefore closely related to their anatomic locations (53,54). Subcutaneous lesions are adequately treated with wide surgical excision, including a cuff of surrounding normal tissue. With adequate initial resection, local recurrence of subcutaneous lesions is rare to nonexistent as reported by Azumi and colleagues (55).

In contradistinction, deep-seated, well-differentiated liposarcomas have significant risk of local recurrence. The rate of local recurrence is 43% for extremity lesions, 70% for groin lesions, and 91% for retroperitoneal lesions (2–5,7,8,10,54,56). These rates are high, particularly for retroperitoneal lesions, because extensive tumor makes it difficult to obtain free surgical margins (particularly when close to neurovascular structures). In these cases, radiation therapy may be employed as an adjunct to surgical resection in attempt to avoid local recurrence. Disease-related mortality, typically associated with complications of multiple local recurrences, is significant. Groin and retroperitoneal well-differentiated liposarcomas are associated with mortality rates of 14% and 33%, respectively (2–5,7,8,10,54,56). Extremity lesions are usually not associated with disease-related mortality unless dedifferentiation occurs. We believe these prognostic features further underscore the life-threatening nature of some well-differentiated liposarcomas, and we emphasize the potential drawbacks in the use of the term atypical lipomatous tumor.

	Dedifferentiated Liposarcoma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Clinical Features
Dedifferentiated liposarcoma represents a biphasic neoplasm, with one component being a well-differentiated liposarcoma and the other a non-adipose cellular sarcoma. Men and women are affected approximately equally, with a peak prevalence in the 7th decade (similar to the age group affected by well-differentiated liposarcoma). Overall, dedifferentiation occurs in approximately 10% of well-differentiated liposarcomas (57–63).

The risk of dedifferentiation depends substantially on location, and it occurs much more frequently in deep-seated lesions, particularly those in the retroperitoneum (Figs 5, 7). Dedifferentiated retroperitoneal liposarcomas outnumber deep-seated extremity lesions by a 3:1 ratio, with less than 20% of such lesions affecting the head, neck, trunk, and spermatic cord (2–4,7–9). Dedifferentiation in subcutaneous well-differentiated liposarcoma is extremely rare (less than 1% of lesions) but not nonexistent (63). In the AFIP series, 8.9% of all liposarcomas were dedifferentiated lesions, with 4.5% in the upper extremity, 24% in the lower extremity (Fig 6), 66% in the retroperitoneum (Fig 7), and 6% in other locations (6). The estimated risk of dedifferentiation is 15% for retroperitoneal tumors and 5% for deep extremity lesions (2–4,6,7,10), and it has been postulated that this predilection for dedifferentiation occurring more commonly in retroperitoneal lesions depends on time and size rather than site. Because retroperitoneal well-differentiated liposarcomas are present for a much longer time before diagnosis and are therefore larger at detection compared with extremity lesions, the prevalence of dedifferentiation is higher. The average latent period for development of dedifferentiation in well-differentiated liposarcomas followed longitudinally was 7–8 years in one study, although the range can be as long as 17–20 years (10). Dedifferentiation occurred "de novo" (in the original well-differentiated liposarcoma) in 90% of cases, and developed in local recurrent lesions in only 10% (2–4,7–9,64). Two cases of dedifferentiated liposarcoma occurring following irradiation were reported by Brooks and Connor (57). However, the relationship of radiation to the development of dedifferentiated liposarcoma is unclear (57).

View larger version (116K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.  Dedifferentiated liposarcoma of the retroperitoneum in a 67-year-old man who presented with an enlarging abdominal mass. (a) Abdominal radiograph from a barium enema study shows a large abdominal mass that displaces opacified bowel to the left. (b, c) CT images (b obtained at a higher level) reveal the large retroperitoneal and abdominal mass that has three components of differing attenuation, including a lipomatous region (L) with thick septa (arrows); a low-attenuation, high-water content component (W) also with thick septa (arrowheads); and a heterogeneous calcified area (C). (d) Photograph of the resected gross specimen demonstrates the large size of the mass (M). (e) Photograph of the sectioned gross specimen corresponds to the imaging features, with the yellow well-differentiated liposarcoma component (L) with thick septa (arrow), lobular chondrosarcomatous (dedifferentiated focus) region with calcification (C), and hemorrhagic region (H).

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.  Dedifferentiated liposarcoma of the retroperitoneum in a 67-year-old man who presented with an enlarging abdominal mass. (a) Abdominal radiograph from a barium enema study shows a large abdominal mass that displaces opacified bowel to the left. (b, c) CT images (b obtained at a higher level) reveal the large retroperitoneal and abdominal mass that has three components of differing attenuation, including a lipomatous region (L) with thick septa (arrows); a low-attenuation, high-water content component (W) also with thick septa (arrowheads); and a heterogeneous calcified area (C). (d) Photograph of the resected gross specimen demonstrates the large size of the mass (M). (e) Photograph of the sectioned gross specimen corresponds to the imaging features, with the yellow well-differentiated liposarcoma component (L) with thick septa (arrow), lobular chondrosarcomatous (dedifferentiated focus) region with calcification (C), and hemorrhagic region (H).

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.  Dedifferentiated liposarcoma of the retroperitoneum in a 67-year-old man who presented with an enlarging abdominal mass. (a) Abdominal radiograph from a barium enema study shows a large abdominal mass that displaces opacified bowel to the left. (b, c) CT images (b obtained at a higher level) reveal the large retroperitoneal and abdominal mass that has three components of differing attenuation, including a lipomatous region (L) with thick septa (arrows); a low-attenuation, high-water content component (W) also with thick septa (arrowheads); and a heterogeneous calcified area (C). (d) Photograph of the resected gross specimen demonstrates the large size of the mass (M). (e) Photograph of the sectioned gross specimen corresponds to the imaging features, with the yellow well-differentiated liposarcoma component (L) with thick septa (arrow), lobular chondrosarcomatous (dedifferentiated focus) region with calcification (C), and hemorrhagic region (H).

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 7d.  Dedifferentiated liposarcoma of the retroperitoneum in a 67-year-old man who presented with an enlarging abdominal mass. (a) Abdominal radiograph from a barium enema study shows a large abdominal mass that displaces opacified bowel to the left. (b, c) CT images (b obtained at a higher level) reveal the large retroperitoneal and abdominal mass that has three components of differing attenuation, including a lipomatous region (L) with thick septa (arrows); a low-attenuation, high-water content component (W) also with thick septa (arrowheads); and a heterogeneous calcified area (C). (d) Photograph of the resected gross specimen demonstrates the large size of the mass (M). (e) Photograph of the sectioned gross specimen corresponds to the imaging features, with the yellow well-differentiated liposarcoma component (L) with thick septa (arrow), lobular chondrosarcomatous (dedifferentiated focus) region with calcification (C), and hemorrhagic region (H).

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 7e.  Dedifferentiated liposarcoma of the retroperitoneum in a 67-year-old man who presented with an enlarging abdominal mass. (a) Abdominal radiograph from a barium enema study shows a large abdominal mass that displaces opacified bowel to the left. (b, c) CT images (b obtained at a higher level) reveal the large retroperitoneal and abdominal mass that has three components of differing attenuation, including a lipomatous region (L) with thick septa (arrows); a low-attenuation, high-water content component (W) also with thick septa (arrowheads); and a heterogeneous calcified area (C). (d) Photograph of the resected gross specimen demonstrates the large size of the mass (M). (e) Photograph of the sectioned gross specimen corresponds to the imaging features, with the yellow well-differentiated liposarcoma component (L) with thick septa (arrow), lobular chondrosarcomatous (dedifferentiated focus) region with calcification (C), and hemorrhagic region (H).

Pathologic Features
At gross pathologic examination, dedifferentiated liposarcoma appears as a multinodular mass with yellow to yellowish tan, well-differentiated areas (2–4,10). The dedifferentiated foci often appear as distinct admixed tangray regions, with abrupt transition between the two components (Figs 6, 7). The dedifferentiated areas are histologically a high-grade fibrosarcoma or malignant fibrous histiocytoma (undifferentiated high-grade pleomorphic sarcoma) in 90% of cases (Fig 6) (2–4,10). Their mitotic activity is often less than that seen in de novo malignant fibrous histiocytoma, although the spectrum of storioform, myxoid, and inflammatory subtypes is similar. In some cases, there is a mixture of high- and low-grade components in the region of dedifferentiation. However, approximately 10% of cases contain only low-grade components, which may resemble large round cells of carcinoma or melanoma, spindled cells containing whorled structures similar to meningioma or nerve sheath tumor, pericytic pattern or rhabdomyosarcoma, osteosarcoma, chondrosarcoma, or leiomyosarcoma elements (Fig 7) (2–4,10,58,59,65). The finding of supernumerary ring or giant chromosomes derived from the 12q13–15 region in well-differentiated liposarcoma and dedifferentiated liposarcoma provides a histogenetic link between these lesions (2–4,7–10).

Imaging Features
Because dedifferentiation always occurs within a well-differentiated liposarcoma, a dedifferentiated liposarcoma shares radiologic features with the latter lesion. Large components of a dedifferentiated liposarcoma, usually predominant by size, appear identical to the previously described features of well-differentiated liposarcoma seen on radiographs and US, CT, and MR images (Figs 6, 7). However, dedifferentiation is suggested by the additional presence of a focal, nodular nonlipomatous region greater than 1 cm in size (Figs 6, 7). In our experience, the dedifferentiated component is usually larger than 3 cm at imaging (Figs 6, 7). In a minority of cases, the dedifferentiated component may be quite large and may occasionally be the dominant component by size.

In our experience, these nonadipose foci are best detected and evaluated with MR imaging. These areas typically have nonspecific, low to intermediate signal intensity on T1-weighted MR images and intermediate to high signal intensity on T2-weighted MR images (Fig 6) (2,12,33, 41,60). On CT images, these foci have attenuation similar to or slightly lower than that of skeletal muscle. These variations in imaging characteristics are likely related to histologic variations in myxoid (higher water content) and fibrous (with variable collagen content) content in the dedifferentiated region. It is important to recognize these foci, and biopsy must be directed at both the lipomatous and nonlipomatous components to ensure accurate pathologic diagnosis (7,42). Imaging guidance (usually with US or CT) may be needed to direct biopsy of the possible dedifferentiated foci if the area is small or the anatomic region complex.

The imaging differential diagnosis for a focal nodular nonlipomatous component within a well-differentiated liposarcoma includes a region of collagenized tissue, metaplastic mineralization, region of dedifferentiation, and fat necrosis. Areas of metaplastic mineralization should be easily detected with radiography (Fig 6 ), sonography (foci with shadowing), or CT (Fig 7). We postulate that contrast-enhanced MR imaging may be useful for identifying fat necrosis. Although the following hypothesis has not been documented in the scientific literature, we would expect to see only thin peripheral rim enhancement about fat necrosis, as opposed to a diffuse or peripheral nodular pattern of enhancement in a focus of dedifferentiation. In our opinion, it is likely not possible to accurately distinguish a focal fibrotic component in a well-differentiated liposarcoma from a region of dedifferentiation on the basis of imaging characteristics, since the signal intensity patterns from water-sensitive MR pulse sequences overlap. However, we believe it is much more important to understand that biopsy must be directed toward this focus (particularly if it is larger than 1–2 cm) because of the significant implication for treatment and prognosis in dedifferentiated liposarcoma (Figs 1, 6, 7). In our experience, following surgical resection, the use of imaging to detect and localize a possible focus of dedifferentiation is quite helpful to direct more diligent pathologic evaluation of these frequently small regions of differing histologic character within a large well-differentiated liposarcoma.

Treatment and Prognosis
The clinical behavior of dedifferentiated liposarcoma, which reflects the high-grade histologic characteristics of most of these lesions, is more aggressive than well-differentiated liposarcomas. Thus, the treatment approach and prognosis are also different. Dedifferentiated liposarcomas are treated with wide surgical excision and frequently with radiation therapy; chemotherapy may also be used as an adjunct. Dedifferentiated liposarcomas recur locally more rapidly than well-differentiated lesions, with an overall rate of 41% (2,6–10,12). Distant metastases, which most commonly affect the lungs, liver, and bone, are seen in 15%–20% of cases. The overall mortality rate for patients with dedifferentiated liposarcoma is 28%–30% (12). Retroperitoneal lesions have essentially a 100% local recurrence rate and almost invariably lead to death (2,6–10,12).

The overall clinical aggressiveness of dedifferentiated liposarcoma is often less than that of many other high-grade pleomorphic sarcomas. One explanation for this disparity in behavior is the integrity of the TP 53 gene (tumor suppressor gene). In addition, many patients may succumb to the local effects of tumor (visceral, bowel, and genitourinary involvement by retroperitoneal lesions) before distant metastases develop. Finally, it is often difficult to differentiate local metastases from contiguous spread in retroperitoneal tumors (2,7,8,10).

	Myxoid Liposarcoma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Clinical Features
Myxoid liposarcoma is the second most common type of liposarcoma and represents 20%–50% of all liposarcomas (Figs 8–11) (2,3,10,66,67). Myxoid liposarcomas account for 10% of all soft-tissue sarcomas (68). Previously, myxoid and round cell liposarcomas were considered distinct histologic subtypes. However, the WHO Classification of Soft Tissue Tumors has now combined these lesions as myxoid liposarcoma, representing a continuum of these two previous subtypes (2).

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.  Myxoid liposarcoma of the popliteal region in a 60-year-old woman with a painless, slowly growing (over 6 years) mass that had been clinically diagnosed as a popliteal cyst. (a) Lateral radiograph shows a large, nonspecific, soft-tissue mass without radiolucent fat (*). (b) Axial sonogram reveals a heterogeneous mass with both low-echogenicity areas (L), corresponding to myxoid tissue, and regions of higher echogenicity (H). It is not possible to definitively identify fat, although the lesion is not cystic, is not in the expected location of a popliteal cyst, and does not show a neck of fluid extending toward the joint. (c–e) Sagittal T1-weighted (500/20) MR images obtained before (c) and after (d) contrast enhancement and axial T2-weighted (2500/90) (e) MR image show a large heterogeneous intermuscular popliteal mass (arrowheads). The mass is deeper than expected for a Baker cyst, and no neck of fluid extending to the joint is seen. The predominant signal intensity is that of a high-water content mass (M) with low signal intensity with T1-weighting and high signal intensity with T2-weighting. However, focal areas in the septa (arrows in c) and several small (<10% of the tumor volume) nodular regions (F) are isointense relative to subcutaneous fat. After administration of contrast agent, thick and nodular peripheral and septal enhancement is seen, most prominent inferiorly (arrows in d). (f, g) Photograph of the axially sectioned gross specimen (f) and photomicrograph (original magnification, x200, hematoxylin-eosin stain) (g) show the high-water content myxoid regions (M) and adipose areas (arrows) corresponding to the imaging findings.

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.  Myxoid liposarcoma of the popliteal region in a 60-year-old woman with a painless, slowly growing (over 6 years) mass that had been clinically diagnosed as a popliteal cyst. (a) Lateral radiograph shows a large, nonspecific, soft-tissue mass without radiolucent fat (*). (b) Axial sonogram reveals a heterogeneous mass with both low-echogenicity areas (L), corresponding to myxoid tissue, and regions of higher echogenicity (H). It is not possible to definitively identify fat, although the lesion is not cystic, is not in the expected location of a popliteal cyst, and does not show a neck of fluid extending toward the joint. (c–e) Sagittal T1-weighted (500/20) MR images obtained before (c) and after (d) contrast enhancement and axial T2-weighted (2500/90) (e) MR image show a large heterogeneous intermuscular popliteal mass (arrowheads). The mass is deeper than expected for a Baker cyst, and no neck of fluid extending to the joint is seen. The predominant signal intensity is that of a high-water content mass (M) with low signal intensity with T1-weighting and high signal intensity with T2-weighting. However, focal areas in the septa (arrows in c) and several small (<10% of the tumor volume) nodular regions (F) are isointense relative to subcutaneous fat. After administration of contrast agent, thick and nodular peripheral and septal enhancement is seen, most prominent inferiorly (arrows in d). (f, g) Photograph of the axially sectioned gross specimen (f) and photomicrograph (original magnification, x200, hematoxylin-eosin stain) (g) show the high-water content myxoid regions (M) and adipose areas (arrows) corresponding to the imaging findings.

View larger version (90K): [in this window] [in a new window] [Download PPT slide]   Figure 8c.  Myxoid liposarcoma of the popliteal region in a 60-year-old woman with a painless, slowly growing (over 6 years) mass that had been clinically diagnosed as a popliteal cyst. (a) Lateral radiograph shows a large, nonspecific, soft-tissue mass without radiolucent fat (*). (b) Axial sonogram reveals a heterogeneous mass with both low-echogenicity areas (L), corresponding to myxoid tissue, and regions of higher echogenicity (H). It is not possible to definitively identify fat, although the lesion is not cystic, is not in the expected location of a popliteal cyst, and does not show a neck of fluid extending toward the joint. (c–e) Sagittal T1-weighted (500/20) MR images obtained before (c) and after (d) contrast enhancement and axial T2-weighted (2500/90) (e) MR image show a large heterogeneous intermuscular popliteal mass (arrowheads). The mass is deeper than expected for a Baker cyst, and no neck of fluid extending to the joint is seen. The predominant signal intensity is that of a high-water content mass (M) with low signal intensity with T1-weighting and high signal intensity with T2-weighting. However, focal areas in the septa (arrows in c) and several small (<10% of the tumor volume) nodular regions (F) are isointense relative to subcutaneous fat. After administration of contrast agent, thick and nodular peripheral and septal enhancement is seen, most prominent inferiorly (arrows in d). (f, g) Photograph of the axially sectioned gross specimen (f) and photomicrograph (original magnification, x200, hematoxylin-eosin stain) (g) show the high-water content myxoid regions (M) and adipose areas (arrows) corresponding to the imaging findings.

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 8d.  Myxoid liposarcoma of the popliteal region in a 60-year-old woman with a painless, slowly growing (over 6 years) mass that had been clinically diagnosed as a popliteal cyst. (a) Lateral radiograph shows a large, nonspecific, soft-tissue mass without radiolucent fat (*). (b) Axial sonogram reveals a heterogeneous mass with both low-echogenicity areas (L), corresponding to myxoid tissue, and regions of higher echogenicity (H). It is not possible to definitively identify fat, although the lesion is not cystic, is not in the expected location of a popliteal cyst, and does not show a neck of fluid extending toward the joint. (c–e) Sagittal T1-weighted (500/20) MR images obtained before (c) and after (d) contrast enhancement and axial T2-weighted (2500/90) (e) MR image show a large heterogeneous intermuscular popliteal mass (arrowheads). The mass is deeper than expected for a Baker cyst, and no neck of fluid extending to the joint is seen. The predominant signal intensity is that of a high-water content mass (M) with low signal intensity with T1-weighting and high signal intensity with T2-weighting. However, focal areas in the septa (arrows in c) and several small (<10% of the tumor volume) nodular regions (F) are isointense relative to subcutaneous fat. After administration of contrast agent, thick and nodular peripheral and septal enhancement is seen, most prominent inferiorly (arrows in d). (f, g) Photograph of the axially sectioned gross specimen (f) and photomicrograph (original magnification, x200, hematoxylin-eosin stain) (g) show the high-water content myxoid regions (M) and adipose areas (arrows) corresponding to the imaging findings.

View larger version (96K): [in this window] [in a new window] [Download PPT slide]   Figure 8e.  Myxoid liposarcoma of the popliteal region in a 60-year-old woman with a painless, slowly growing (over 6 years) mass that had been clinically diagnosed as a popliteal cyst. (a) Lateral radiograph shows a large, nonspecific, soft-tissue mass without radiolucent fat (*). (b) Axial sonogram reveals a heterogeneous mass with both low-echogenicity areas (L), corresponding to myxoid tissue, and regions of higher echogenicity (H). It is not possible to definitively identify fat, although the lesion is not cystic, is not in the expected location of a popliteal cyst, and does not show a neck of fluid extending toward the joint. (c–e) Sagittal T1-weighted (500/20) MR images obtained before (c) and after (d) contrast enhancement and axial T2-weighted (2500/90) (e) MR image show a large heterogeneous intermuscular popliteal mass (arrowheads). The mass is deeper than expected for a Baker cyst, and no neck of fluid extending to the joint is seen. The predominant signal intensity is that of a high-water content mass (M) with low signal intensity with T1-weighting and high signal intensity with T2-weighting. However, focal areas in the septa (arrows in c) and several small (<10% of the tumor volume) nodular regions (F) are isointense relative to subcutaneous fat. After administration of contrast agent, thick and nodular peripheral and septal enhancement is seen, most prominent inferiorly (arrows in d). (f, g) Photograph of the axially sectioned gross specimen (f) and photomicrograph (original magnification, x200, hematoxylin-eosin stain) (g) show the high-water content myxoid regions (M) and adipose areas (arrows) corresponding to the imaging findings.

View larger version (117K): [in this window] [in a new window] [Download PPT slide]   Figure 8f.  Myxoid liposarcoma of the popliteal region in a 60-year-old woman with a painless, slowly growing (over 6 years) mass that had been clinically diagnosed as a popliteal cyst. (a) Lateral radiograph shows a large, nonspecific, soft-tissue mass without radiolucent fat (*). (b) Axial sonogram reveals a heterogeneous mass with both low-echogenicity areas (L), corresponding to myxoid tissue, and regions of higher echogenicity (H). It is not possible to definitively identify fat, although the lesion is not cystic, is not in the expected location of a popliteal cyst, and does not show a neck of fluid extending toward the joint. (c–e) Sagittal T1-weighted (500/20) MR images obtained before (c) and after (d) contrast enhancement and axial T2-weighted (2500/90) (e) MR image show a large heterogeneous intermuscular popliteal mass (arrowheads). The mass is deeper than expected for a Baker cyst, and no neck of fluid extending to the joint is seen. The predominant signal intensity is that of a high-water content mass (M) with low signal intensity with T1-weighting and high signal intensity with T2-weighting. However, focal areas in the septa (arrows in c) and several small (<10% of the tumor volume) nodular regions (F) are isointense relative to subcutaneous fat. After administration of contrast agent, thick and nodular peripheral and septal enhancement is seen, most prominent inferiorly (arrows in d). (f, g) Photograph of the axially sectioned gross specimen (f) and photomicrograph (original magnification, x200, hematoxylin-eosin stain) (g) show the high-water content myxoid regions (M) and adipose areas (arrows) corresponding to the imaging findings.

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 8g.  Myxoid liposarcoma of the popliteal region in a 60-year-old woman with a painless, slowly growing (over 6 years) mass that had been clinically diagnosed as a popliteal cyst. (a) Lateral radiograph shows a large, nonspecific, soft-tissue mass without radiolucent fat (*). (b) Axial sonogram reveals a heterogeneous mass with both low-echogenicity areas (L), corresponding to myxoid tissue, and regions of higher echogenicity (H). It is not possible to definitively identify fat, although the lesion is not cystic, is not in the expected location of a popliteal cyst, and does not show a neck of fluid extending toward the joint. (c–e) Sagittal T1-weighted (500/20) MR images obtained before (c) and after (d) contrast enhancement and axial T2-weighted (2500/90) (e) MR image show a large heterogeneous intermuscular popliteal mass (arrowheads). The mass is deeper than expected for a Baker cyst, and no neck of fluid extending to the joint is seen. The predominant signal intensity is that of a high-water content mass (M) with low signal intensity with T1-weighting and high signal intensity with T2-weighting. However, focal areas in the septa (arrows in c) and several small (<10% of the tumor volume) nodular regions (F) are isointense relative to subcutaneous fat. After administration of contrast agent, thick and nodular peripheral and septal enhancement is seen, most prominent inferiorly (arrows in d). (f, g) Photograph of the axially sectioned gross specimen (f) and photomicrograph (original magnification, x200, hematoxylin-eosin stain) (g) show the high-water content myxoid regions (M) and adipose areas (arrows) corresponding to the imaging findings.

View larger version (140K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.  Myxoid liposarcoma in the distal thigh in a 16-year-old boy with a slowly enlarging mass with subsequent development of pleural metastasis. (a) CT scan of the distal thigh shows an intermuscular mass with predominant attenuation lower than that of muscle (*) that displaces adjacent muscle (M). Several round foci of very low attenuation (arrows) similar to that of fat are also seen. (b, c) Axial T1-weighted (600/20) (b) and T2-weighted (2000/80) (c) MR images reveal an intermuscular posterior compartment mass (*) of predominantly high-water content (low signal intensity with T1-weighting and very high signal intensity with T2-weighting). Several nodular foci (arrows) of tissue similar or identical to subcutaneous fat are identified. (d) Photograph of the axially sectioned gross specimen demonstrates pathologic features identical to those seen at imaging: high-water content myxoid areas (m) and focal nodules containing fat (arrows). (e, f) Chest radiograph (e) and CT scan (f) obtained several years later reveal a pleural-based metastasis (P). The low attenuation seen on the CT scan reflects the high-water content myxoid tissue.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.  Myxoid liposarcoma in the distal thigh in a 16-year-old boy with a slowly enlarging mass with subsequent development of pleural metastasis. (a) CT scan of the distal thigh shows an intermuscular mass with predominant attenuation lower than that of muscle (*) that displaces adjacent muscle (M). Several round foci of very low attenuation (arrows) similar to that of fat are also seen. (b, c) Axial T1-weighted (600/20) (b) and T2-weighted (2000/80) (c) MR images reveal an intermuscular posterior compartment mass (*) of predominantly high-water content (low signal intensity with T1-weighting and very high signal intensity with T2-weighting). Several nodular foci (arrows) of tissue similar or identical to subcutaneous fat are identified. (d) Photograph of the axially sectioned gross specimen demonstrates pathologic features identical to those seen at imaging: high-water content myxoid areas (m) and focal nodules containing fat (arrows). (e, f) Chest radiograph (e) and CT scan (f) obtained several years later reveal a pleural-based metastasis (P). The low attenuation seen on the CT scan reflects the high-water content myxoid tissue.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 9c.  Myxoid liposarcoma in the distal thigh in a 16-year-old boy with a slowly enlarging mass with subsequent development of pleural metastasis. (a) CT scan of the distal thigh shows an intermuscular mass with predominant attenuation lower than that of muscle (*) that displaces adjacent muscle (M). Several round foci of very low attenuation (arrows) similar to that of fat are also seen. (b, c) Axial T1-weighted (600/20) (b) and T2-weighted (2000/80) (c) MR images reveal an intermuscular posterior compartment mass (*) of predominantly high-water content (low signal intensity with T1-weighting and very high signal intensity with T2-weighting). Several nodular foci (arrows) of tissue similar or identical to subcutaneous fat are identified. (d) Photograph of the axially sectioned gross specimen demonstrates pathologic features identical to those seen at imaging: high-water content myxoid areas (m) and focal nodules containing fat (arrows). (e, f) Chest radiograph (e) and CT scan (f) obtained several years later reveal a pleural-based metastasis (P). The low attenuation seen on the CT scan reflects the high-water content myxoid tissue.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 9d.  Myxoid liposarcoma in the distal thigh in a 16-year-old boy with a slowly enlarging mass with subsequent development of pleural metastasis. (a) CT scan of the distal thigh shows an intermuscular mass with predominant attenuation lower than that of muscle (*) that displaces adjacent muscle (M). Several round foci of very low attenuation (arrows) similar to that of fat are also seen. (b, c) Axial T1-weighted (600/20) (b) and T2-weighted (2000/80) (c) MR images reveal an intermuscular posterior compartment mass (*) of predominantly high-water content (low signal intensity with T1-weighting and very high signal intensity with T2-weighting). Several nodular foci (arrows) of tissue similar or identical to subcutaneous fat are identified. (d) Photograph of the axially sectioned gross specimen demonstrates pathologic features identical to those seen at imaging: high-water content myxoid areas (m) and focal nodules containing fat (arrows). (e, f) Chest radiograph (e) and CT scan (f) obtained several years later reveal a pleural-based metastasis (P). The low attenuation seen on the CT scan reflects the high-water content myxoid tissue.

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 9e.  Myxoid liposarcoma in the distal thigh in a 16-year-old boy with a slowly enlarging mass with subsequent development of pleural metastasis. (a) CT scan of the distal thigh shows an intermuscular mass with predominant attenuation lower than that of muscle (*) that displaces adjacent muscle (M). Several round foci of very low attenuation (arrows) similar to that of fat are also seen. (b, c) Axial T1-weighted (600/20) (b) and T2-weighted (2000/80) (c) MR images reveal an intermuscular posterior compartment mass (*) of predominantly high-water content (low signal intensity with T1-weighting and very high signal intensity with T2-weighting). Several nodular foci (arrows) of tissue similar or identical to subcutaneous fat are identified. (d) Photograph of the axially sectioned gross specimen demonstrates pathologic features identical to those seen at imaging: high-water content myxoid areas (m) and focal nodules containing fat (arrows). (e, f) Chest radiograph (e) and CT scan (f) obtained several years later reveal a pleural-based metastasis (P). The low attenuation seen on the CT scan reflects the high-water content myxoid tissue.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 9f.  Myxoid liposarcoma in the distal thigh in a 16-year-old boy with a slowly enlarging mass with subsequent development of pleural metastasis. (a) CT scan of the distal thigh shows an intermuscular mass with predominant attenuation lower than that of muscle (*) that displaces adjacent muscle (M). Several round foci of very low attenuation (arrows) similar to that of fat are also seen. (b, c) Axial T1-weighted (600/20) (b) and T2-weighted (2000/80) (c) MR images reveal an intermuscular posterior compartment mass (*) of predominantly high-water content (low signal intensity with T1-weighting and very high signal intensity with T2-weighting). Several nodular foci (arrows) of tissue similar or identical to subcutaneous fat are identified. (d) Photograph of the axially sectioned gross specimen demonstrates pathologic features identical to those seen at imaging: high-water content myxoid areas (m) and focal nodules containing fat (arrows). (e, f) Chest radiograph (e) and CT scan (f) obtained several years later reveal a pleural-based metastasis (P). The low attenuation seen on the CT scan reflects the high-water content myxoid tissue.

View larger version (157K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Myxoid liposarcoma simulating a cyst in a 57-year-old man with a slowly enlarging, painless mass in the subcutaneous tissues of the distal thigh (the mass was first noticed after mild trauma 18 months previously). (a, b) Coronal T1-weighted (600/25) (a) and T2-weighted (2000/50) (b) MR images show a relatively well-defined homogeneous mass (*) with low to intermediate signal intensity with T1-weighting and homogeneous high signal intensity with T2-weighting. No fat is apparent. Although the imaging characteristics simulate a cyst, the location is markedly atypical, and the case required further imaging to exclude a myxoid tumor masquerading as a cyst (cyst mimicker) (c, d) Coronal T1-weighted contrast-enhanced fat-suppressed MR image (600/25) (c) and axial Doppler sonogram (d) demonstrate the solid noncystic nature of the mass (*), which had peripheral nodular enhancement at MR imaging (c) and hyperechogenicity at sonography (rather than being anechoic, like a cyst). Arrowheads = vessels. (e) Photograph of the axially sectioned gross specimen reveals the solid but gelatinous high-water content myxoid liposarcoma.

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Myxoid liposarcoma simulating a cyst in a 57-year-old man with a slowly enlarging, painless mass in the subcutaneous tissues of the distal thigh (the mass was first noticed after mild trauma 18 months previously). (a, b) Coronal T1-weighted (600/25) (a) and T2-weighted (2000/50) (b) MR images show a relatively well-defined homogeneous mass (*) with low to intermediate signal intensity with T1-weighting and homogeneous high signal intensity with T2-weighting. No fat is apparent. Although the imaging characteristics simulate a cyst, the location is markedly atypical, and the case required further imaging to exclude a myxoid tumor masquerading as a cyst (cyst mimicker) (c, d) Coronal T1-weighted contrast-enhanced fat-suppressed MR image (600/25) (c) and axial Doppler sonogram (d) demonstrate the solid noncystic nature of the mass (*), which had peripheral nodular enhancement at MR imaging (c) and hyperechogenicity at sonography (rather than being anechoic, like a cyst). Arrowheads = vessels. (e) Photograph of the axially sectioned gross specimen reveals the solid but gelatinous high-water content myxoid liposarcoma.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 10c.  Myxoid liposarcoma simulating a cyst in a 57-year-old man with a slowly enlarging, painless mass in the subcutaneous tissues of the distal thigh (the mass was first noticed after mild trauma 18 months previously). (a, b) Coronal T1-weighted (600/25) (a) and T2-weighted (2000/50) (b) MR images show a relatively well-defined homogeneous mass (*) with low to intermediate signal intensity with T1-weighting and homogeneous high signal intensity with T2-weighting. No fat is apparent. Although the imaging characteristics simulate a cyst, the location is markedly atypical, and the case required further imaging to exclude a myxoid tumor masquerading as a cyst (cyst mimicker) (c, d) Coronal T1-weighted contrast-enhanced fat-suppressed MR image (600/25) (c) and axial Doppler sonogram (d) demonstrate the solid noncystic nature of the mass (*), which had peripheral nodular enhancement at MR imaging (c) and hyperechogenicity at sonography (rather than being anechoic, like a cyst). Arrowheads = vessels. (e) Photograph of the axially sectioned gross specimen reveals the solid but gelatinous high-water content myxoid liposarcoma.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 10d.  Myxoid liposarcoma simulating a cyst in a 57-year-old man with a slowly enlarging, painless mass in the subcutaneous tissues of the distal thigh (the mass was first noticed after mild trauma 18 months previously). (a, b) Coronal T1-weighted (600/25) (a) and T2-weighted (2000/50) (b) MR images show a relatively well-defined homogeneous mass (*) with low to intermediate signal intensity with T1-weighting and homogeneous high signal intensity with T2-weighting. No fat is apparent. Although the imaging characteristics simulate a cyst, the location is markedly atypical, and the case required further imaging to exclude a myxoid tumor masquerading as a cyst (cyst mimicker) (c, d) Coronal T1-weighted contrast-enhanced fat-suppressed MR image (600/25) (c) and axial Doppler sonogram (d) demonstrate the solid noncystic nature of the mass (*), which had peripheral nodular enhancement at MR imaging (c) and hyperechogenicity at sonography (rather than being anechoic, like a cyst). Arrowheads = vessels. (e) Photograph of the axially sectioned gross specimen reveals the solid but gelatinous high-water content myxoid liposarcoma.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 10e.  Myxoid liposarcoma simulating a cyst in a 57-year-old man with a slowly enlarging, painless mass in the subcutaneous tissues of the distal thigh (the mass was first noticed after mild trauma 18 months previously). (a, b) Coronal T1-weighted (600/25) (a) and T2-weighted (2000/50) (b) MR images show a relatively well-defined homogeneous mass (*) with low to intermediate signal intensity with T1-weighting and homogeneous high signal intensity with T2-weighting. No fat is apparent. Although the imaging characteristics simulate a cyst, the location is markedly atypical, and the case required further imaging to exclude a myxoid tumor masquerading as a cyst (cyst mimicker) (c, d) Coronal T1-weighted contrast-enhanced fat-suppressed MR image (600/25) (c) and axial Doppler sonogram (d) demonstrate the solid noncystic nature of the mass (*), which had peripheral nodular enhancement at MR imaging (c) and hyperechogenicity at sonography (rather than being anechoic, like a cyst). Arrowheads = vessels. (e) Photograph of the axially sectioned gross specimen reveals the solid but gelatinous high-water content myxoid liposarcoma.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.  Myxoid liposarcoma with prominent round cell component in the axilla of a 44-year-old woman who presented with a slowly enlarging mass. (a) CT scan shows a heterogeneous inter-muscular axillary mass (open arrows) with low-attenuation areas (L) and regions similar to muscle (arrowheads). A minute focus suggestive of fat is also seen (solid arrow). (b–d) Axial T1-weighted (800/ 11) MR images obtained before (b) and after (also with fat suppression) (c) contrast enhancement and a T2-weighted (6200/102) (d) fat-suppressed MR image show that the mass contains a subtle area of adipose tissue posteriorly (arrows) that is isointense relative to subcutaneous fat. Other regions of nonspecific solid tissue diffusely enhance. The signal intensity is not as high as that of typical myxoid tissue. (e) Photograph of the axially sectioned gross specimen demonstrates features of a heterogeneous multinodular partially myxoid mass (m) with a prominent round cell component (R) and subtle adipose tissue (arrows). (f) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows areas of high-water content myxoid tissue (m, bottom) and a prominent cellular region (round cells [R], top). The round cell component constituted more than 25% of the lesion.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.  Myxoid liposarcoma with prominent round cell component in the axilla of a 44-year-old woman who presented with a slowly enlarging mass. (a) CT scan shows a heterogeneous inter-muscular axillary mass (open arrows) with low-attenuation areas (L) and regions similar to muscle (arrowheads). A minute focus suggestive of fat is also seen (solid arrow). (b–d) Axial T1-weighted (800/ 11) MR images obtained before (b) and after (also with fat suppression) (c) contrast enhancement and a T2-weighted (6200/102) (d) fat-suppressed MR image show that the mass contains a subtle area of adipose tissue posteriorly (arrows) that is isointense relative to subcutaneous fat. Other regions of nonspecific solid tissue diffusely enhance. The signal intensity is not as high as that of typical myxoid tissue. (e) Photograph of the axially sectioned gross specimen demonstrates features of a heterogeneous multinodular partially myxoid mass (m) with a prominent round cell component (R) and subtle adipose tissue (arrows). (f) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows areas of high-water content myxoid tissue (m, bottom) and a prominent cellular region (round cells [R], top). The round cell component constituted more than 25% of the lesion.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 11c.  Myxoid liposarcoma with prominent round cell component in the axilla of a 44-year-old woman who presented with a slowly enlarging mass. (a) CT scan shows a heterogeneous inter-muscular axillary mass (open arrows) with low-attenuation areas (L) and regions similar to muscle (arrowheads). A minute focus suggestive of fat is also seen (solid arrow). (b–d) Axial T1-weighted (800/ 11) MR images obtained before (b) and after (also with fat suppression) (c) contrast enhancement and a T2-weighted (6200/102) (d) fat-suppressed MR image show that the mass contains a subtle area of adipose tissue posteriorly (arrows) that is isointense relative to subcutaneous fat. Other regions of nonspecific solid tissue diffusely enhance. The signal intensity is not as high as that of typical myxoid tissue. (e) Photograph of the axially sectioned gross specimen demonstrates features of a heterogeneous multinodular partially myxoid mass (m) with a prominent round cell component (R) and subtle adipose tissue (arrows). (f) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows areas of high-water content myxoid tissue (m, bottom) and a prominent cellular region (round cells [R], top). The round cell component constituted more than 25% of the lesion.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 11d.  Myxoid liposarcoma with prominent round cell component in the axilla of a 44-year-old woman who presented with a slowly enlarging mass. (a) CT scan shows a heterogeneous inter-muscular axillary mass (open arrows) with low-attenuation areas (L) and regions similar to muscle (arrowheads). A minute focus suggestive of fat is also seen (solid arrow). (b–d) Axial T1-weighted (800/ 11) MR images obtained before (b) and after (also with fat suppression) (c) contrast enhancement and a T2-weighted (6200/102) (d) fat-suppressed MR image show that the mass contains a subtle area of adipose tissue posteriorly (arrows) that is isointense relative to subcutaneous fat. Other regions of nonspecific solid tissue diffusely enhance. The signal intensity is not as high as that of typical myxoid tissue. (e) Photograph of the axially sectioned gross specimen demonstrates features of a heterogeneous multinodular partially myxoid mass (m) with a prominent round cell component (R) and subtle adipose tissue (arrows). (f) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows areas of high-water content myxoid tissue (m, bottom) and a prominent cellular region (round cells [R], top). The round cell component constituted more than 25% of the lesion.

View larger version (73K): [in this window] [in a new window] [Download PPT slide]   Figure 11e.  Myxoid liposarcoma with prominent round cell component in the axilla of a 44-year-old woman who presented with a slowly enlarging mass. (a) CT scan shows a heterogeneous inter-muscular axillary mass (open arrows) with low-attenuation areas (L) and regions similar to muscle (arrowheads). A minute focus suggestive of fat is also seen (solid arrow). (b–d) Axial T1-weighted (800/ 11) MR images obtained before (b) and after (also with fat suppression) (c) contrast enhancement and a T2-weighted (6200/102) (d) fat-suppressed MR image show that the mass contains a subtle area of adipose tissue posteriorly (arrows) that is isointense relative to subcutaneous fat. Other regions of nonspecific solid tissue diffusely enhance. The signal intensity is not as high as that of typical myxoid tissue. (e) Photograph of the axially sectioned gross specimen demonstrates features of a heterogeneous multinodular partially myxoid mass (m) with a prominent round cell component (R) and subtle adipose tissue (arrows). (f) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows areas of high-water content myxoid tissue (m, bottom) and a prominent cellular region (round cells [R], top). The round cell component constituted more than 25% of the lesion.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 11f.  Myxoid liposarcoma with prominent round cell component in the axilla of a 44-year-old woman who presented with a slowly enlarging mass. (a) CT scan shows a heterogeneous inter-muscular axillary mass (open arrows) with low-attenuation areas (L) and regions similar to muscle (arrowheads). A minute focus suggestive of fat is also seen (solid arrow). (b–d) Axial T1-weighted (800/ 11) MR images obtained before (b) and after (also with fat suppression) (c) contrast enhancement and a T2-weighted (6200/102) (d) fat-suppressed MR image show that the mass contains a subtle area of adipose tissue posteriorly (arrows) that is isointense relative to subcutaneous fat. Other regions of nonspecific solid tissue diffusely enhance. The signal intensity is not as high as that of typical myxoid tissue. (e) Photograph of the axially sectioned gross specimen demonstrates features of a heterogeneous multinodular partially myxoid mass (m) with a prominent round cell component (R) and subtle adipose tissue (arrows). (f) Photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows areas of high-water content myxoid tissue (m, bottom) and a prominent cellular region (round cells [R], top). The round cell component constituted more than 25% of the lesion.

Extremity myxoid liposarcomas are most frequently intermuscular lesions (70%–80% of cases), and an origin in muscle or subcutaneous location is less common (Figs 8–11) (2–5,7,8,10, 66,67). These lesions predominantly affect the lower extremity (75%–80% of cases), particularly the medial thigh and popliteal regions (Figs 8–10) (2–5,7,8,10,66,67). Other locations in the lower extremities include the groin, buttock, and calf. The upper extremity accounts for 5% of lesions (Fig 11), and the retroperitoneum, 8% (2–5,7,8,10,66,67).

The clinical appearance of myxoid liposarcoma is that of a painless, soft-tissue mass. Lesions may be quite large (>15 cm) at presentation, similar to well-differentiated liposarcoma (2,10).

Pathologic Features
Myxoid liposarcomas are well-circumscribed, multinodular masses (Figs 8–11) whose gross pathologic appearance varies depending on the degree of myxoid and round cell components. Predominantly myxoid lesions are gelatinous, whereas lesions with focal areas of round cells contain opaque white nodules. Lesions with a predominant round cell component have a non-specific, white fleshy appearance similar to that of other soft-tissue sarcomas. Myxoid liposarcomas are generally considered intermediate grade lesions if predominantly myxoid, but high-grade if they contain a substantial round cell component.

At histologic analysis, myxoid liposarcoma consists of well-delineated lobules of myxoid tissue; a characteristic, delicate, arborizing capillary network; and primitive uniform mesenchymal cells with variable numbers of usually monovacuolated and sometimes bivacuolated lipoblasts, particularly at the periphery of the lobules (Fig 11 ). Mitoses are scant. Areas of relatively mature adipose tissue are usually present but sparse (<10% of the lesion overall volume) (Fig 11) (2,4,7,8,10,24,66). Pooling of the myxoid matrix can occur and, if extensive, results in a "pulmonary edema" pattern. Hemorrhage may also be present.

Round cell components causing increased cellularity are variable in this group of lesions. These areas are characterized by solid sheets of primitive round cells, which replace the myxoid stroma and typical vascular pattern (Fig 11). The myxoid and round cell components are often juxtaposed, with higher mitotic activity and necrosis found in the round cell component. There is often a gradual transition from myxoid areas to these cellular regions, an appearance that suggests a histologic continuum of these lesions. Myxoid liposarcoma is genetically characterized by the reciprocal translocation of t(12;16)(q13;p11). This cytogenetic marker is present in more than 90% of cases (2,10,29,66,72,73). It is both highly specific and sensitive, since it is not associated with other histologic mimics such as myxofibrosarcoma or well-differentiated liposarcoma with myxoid change.

Imaging Features
Radiographs of myxoid liposarcoma may appear normal or more frequently reveal a nonspecific soft-tissue mass. Calcification occurs much less frequently than with well-differentiated liposarcoma (74). Similarly, radiolucent fat is also seen much less often compared with well-differentiated liposarcoma, owing to the much smaller volume of adipose tissue (often <10%) in these lesions (7,12,33,75,76).

Sonographic appearance of myxoid liposarcoma has not been extensively reported (34,35, 37,75–77). In our experience, US reveals a complex, well-defined, hypoechoic but solid, noncystic mass with posterior acoustic enhancement (Figs 8, 10). Although adipose tissue typically cannot be definitively identified in most cases at sonographic evaluation to suggest the diagnosis, US findings can be very helpful in several specific clinical scenarios. For example, in cases in which the CT or MR imaging findings suggest a cyst, sonography can demonstrate that the mass is not truly a cyst (anechoic mass that may contain thin septa) and thus further investigation with biopsy is necessary (Figs 8 , 10). In addition, a popliteal location of myxoid liposarcomas is common, and such lesions may simulate a Baker cyst. However, as described by Ward and colleagues (77), all popliteal cysts have a fluid-filled neck that extends to the joint between the gastrocnemius and semi-membranous tendons. This finding is not seen with a popliteal myxoid liposarcoma, since these lesions are not as superficial as a Baker cyst, and again the mass does not meet sonographic criteria for a true cyst (Fig 10).

At CT and MR imaging, myxoid liposarcoma often have a pathognomonic appearance (Figs 8, 9) (41,42,75–77). Myxoid liposarcomas are typically large, well-defined, and multilobulated intermuscular lesions. The high water content of the lesion is reflected as predominant low attenuation on CT images, low signal intensity on T1-weighted MR images, and marked high signal intensity on T2-weighted MR images (Figs 8, 9). However, the pathognomonic feature is the adipose tissue seen in the mass (Figs 8, 9). MR imaging is superior to CT in this important depiction of fat, owing to its improved contrast resolution. Fat also typically constitutes only a small volume of the overall mass size (<10% of the lesion) and is often seen in septa (lacy or linear pattern) or as subtle small nodules in the lesion (Figs 8–10). This pathognomonic appearance of fatty septa or small adipose nodules in a myxoid mass has been reported in 42%–78% of cases (41,76). However, in our experience, 90%–95% of myxoid liposarcomas demonstrate fat at MR imaging (75). Identification of this subtle fat is aided by the careful comparison of T1- and T2-weighted images in the same plane (usually axial is optimal). Use of fat-suppression or fat-saturation techniques can also be very helpful to further increase confidence in the detection of adipose content in these regions.

According to the literature, myxoid liposarcoma may simulate a cyst because of its homogeneous low attenuation on CT images or homogeneous low to intermediate signal intensity on T1-weighted MR images and very high signal intensity on T2-weighted MR images in 21%–22% of cases (Fig 10) (12,41,76). In our experience, the prevalence of myxoid liposarcoma simulating a cyst ("cyst mimicker") at MR imaging is much lower (5%–10%), but this remains an important radiologic diagnostic dilemma (75). We believe that the strongest indications that one may be dealing with a "cyst mimicker" such as a myxoid liposarcoma include the following observations: (a) when the lesion is not in the expected location of a synovial cyst or ganglion (Fig 10), (b) when the lesion has no thick wall or surrounding edema, or (c) when there is no appropriate clinical history to suggest abscess or liquefied hematoma. In our opinion, these features mandate further radiologic evaluation with either US or contrast material enhancement. Those lesions identified as solid masses (with high water content) require biopsy (Fig 10). Myxoma is another diagnostic consideration, although myxomas are generally intramuscular lesions with surrounding muscle atrophy and edema, all manifestations not seen in myxoid liposarcoma (44,78,79).

Myxoid liposarcomas enhance with contrast material at MR imaging, a characteristic that easily distinguishes these lesions from a cystic mass (Figs 8, 10, 11). Tateishi and colleagues (80) reported on the patterns of myxoid liposarcoma enhancement at MR imaging, which included peripheral nodular (61% of cases), central nodular (44%), and diffuse (17%). Their findings are in marked contrast with those for a true cystic mass, which enhances with thin and nonnodular, peripheral and septal patterns only.

Myxoid liposarcomas with more prominent round cell components may demonstrate areas of relatively lower water content at US, CT, and MR imaging (Fig 11) (12,41,75,76,80). These areas may have nonspecific features of solid tissue with intermediate echogenicity on sonograms, attenuation similar to that of muscle on CT scans, and intermediate signal intensity on T1-and T2-weighted MR images (Fig 11). Tateishi and colleagues (80) also reported that absence of thin septa or capsule and pronounced contrast enhancement at MR imaging are findings that suggest a more prominent round cell component and resultant worse prognosis. In our experience, biopsy of these subtle adipose areas in these often large myxoid neoplasms (as well as identification after surgical resection) improves the pathologist’s ability and confidence to determine the specific histologic diagnosis.

Treatment and Prognosis
The treatment of choice for myxoid liposarcoma is wide surgical excision. In cases with incomplete or marginal resection owing to lesion size, lesion extent, or its proximity to the neurovascular bundle, radiation therapy is often used to reduce local recurrence (2,4,7,8,10). Adjunct chemotherapy may also prove beneficial in treatment of myxoid liposarcoma.

The rate of metastatic disease is significantly increased for patients whose myxoid liposarcomas contain a greater proportion of round cell component. In a study by Evans (14), the 10-year mortality rate ranged from 30% for patients with 5%–25% round cell component to 60% for patients with greater than 25% round cell component. The study by Kilpatrick et al (66) also correlated metastatic rate with the proportion of round cell component. In this study, metastases developed in 23% of patients with 0%–5% round cell component, 35% of patients with 5%–10% round cell component, and 56% of patients with greater than 25% round cell component (66). Additional factors associated with a worse prognosis are patient age greater than 45 years and the histologic presence of spontaneous necrosis. The overall 5-year survival rate for patients with myxoid liposarcoma ranges from 47% to 77% (2,7,9,10, 12,14,66).

Unlike the other subtypes of liposarcoma, myxoid lesions have a strong predilection for extrapulmonary metastases (Fig 9). In a study by Pearlstone and colleagues (81), 94% of patients with metastatic myxoid liposarcoma also developed metastases in extrapulmonary soft-tissue sites, including the retroperitoneum, thorax (chest wall, pericardium, pleura), and pelvis. These metastatic lesions often maintain their myxoid characteristics on images (Fig 9). Pulmonary involvement is seen in only 6% of patients (2,10,12,66).

	Pleomorphic Liposarcoma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Clinical Features
Pleomorphic liposarcoma is the least common subtype of liposarcoma, representing only 5%–15% of all liposarcomatous lesions (2,4,8–10, 12,82–84). This type of liposarcoma accounts for 20% of all pleomorphic sarcomas (2). The majority of these lesions arise in patients older than 50 years of age; men and women are affected equally (2,8,10).

Pleomorphic lesions most frequently affect an intramuscular location, and similar to other subtypes of liposarcoma, the lower extremity is most commonly involved (56% of cases) (Figs 12 , 13) (12). The upper extremity is involved in 20% of cases and the retroperitoneum in 9% (12). Unusual sites affected include the mediastinum, paratesticular area, scalp (and other subcutaneous sites), abdominal cavity, pelvic cavity, and the orbit (2,7,8,10,12).

View larger version (177K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.  Pleomorphic liposarcoma of the thigh in a 59-year-old man with a 1-year history of a rapidly enlarging, painless mass. (a–c) Axial T1-weighted (550/6) MR images obtained before (a) and after (also with fat suppression) (b) contrast enhancement and a coronal STIR MR image (1800/40/160) (c) show a large anterior compartment intramuscular mass (arrows). The predominant portion of the mass reveals nonspecific, intermediate signal intensity with T1-weighting and high signal intensity with T2-weighting. Small focus of higher signal intensity similar to that of fat (arrowhead in a) seen on the unenhanced T1-weighted image and showing fat saturation with STIR sequences (arrowhead in c) represents a small focus of fat in the lesion. Other areas lacking enhancement are less vascularized or necrotic regions. (d) Photograph of the axially sectioned gross specimen shows several subtle areas of fat (arrows) with other nonspecific nonlipomatous pleomorphic sarcoma regions.

View larger version (179K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.  Pleomorphic liposarcoma of the thigh in a 59-year-old man with a 1-year history of a rapidly enlarging, painless mass. (a–c) Axial T1-weighted (550/6) MR images obtained before (a) and after (also with fat suppression) (b) contrast enhancement and a coronal STIR MR image (1800/40/160) (c) show a large anterior compartment intramuscular mass (arrows). The predominant portion of the mass reveals nonspecific, intermediate signal intensity with T1-weighting and high signal intensity with T2-weighting. Small focus of higher signal intensity similar to that of fat (arrowhead in a) seen on the unenhanced T1-weighted image and showing fat saturation with STIR sequences (arrowhead in c) represents a small focus of fat in the lesion. Other areas lacking enhancement are less vascularized or necrotic regions. (d) Photograph of the axially sectioned gross specimen shows several subtle areas of fat (arrows) with other nonspecific nonlipomatous pleomorphic sarcoma regions.

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 12c.  Pleomorphic liposarcoma of the thigh in a 59-year-old man with a 1-year history of a rapidly enlarging, painless mass. (a–c) Axial T1-weighted (550/6) MR images obtained before (a) and after (also with fat suppression) (b) contrast enhancement and a coronal STIR MR image (1800/40/160) (c) show a large anterior compartment intramuscular mass (arrows). The predominant portion of the mass reveals nonspecific, intermediate signal intensity with T1-weighting and high signal intensity with T2-weighting. Small focus of higher signal intensity similar to that of fat (arrowhead in a) seen on the unenhanced T1-weighted image and showing fat saturation with STIR sequences (arrowhead in c) represents a small focus of fat in the lesion. Other areas lacking enhancement are less vascularized or necrotic regions. (d) Photograph of the axially sectioned gross specimen shows several subtle areas of fat (arrows) with other nonspecific nonlipomatous pleomorphic sarcoma regions.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 12d.  Pleomorphic liposarcoma of the thigh in a 59-year-old man with a 1-year history of a rapidly enlarging, painless mass. (a–c) Axial T1-weighted (550/6) MR images obtained before (a) and after (also with fat suppression) (b) contrast enhancement and a coronal STIR MR image (1800/40/160) (c) show a large anterior compartment intramuscular mass (arrows). The predominant portion of the mass reveals nonspecific, intermediate signal intensity with T1-weighting and high signal intensity with T2-weighting. Small focus of higher signal intensity similar to that of fat (arrowhead in a) seen on the unenhanced T1-weighted image and showing fat saturation with STIR sequences (arrowhead in c) represents a small focus of fat in the lesion. Other areas lacking enhancement are less vascularized or necrotic regions. (d) Photograph of the axially sectioned gross specimen shows several subtle areas of fat (arrows) with other nonspecific nonlipomatous pleomorphic sarcoma regions.

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.  Pleomorphic liposarcoma of the thigh in a 47-year-old woman who presented with an enlarging thigh mass. (a–c) Axial T1-weighted MR images obtained before (500/8) (a) and after (600/8) (b) contrast enhancement and a T2-weighted MR image with fat suppression (4566/66) (c) reveal a large heterogeneous intramuscular and intermuscular mass (open arrows) in the posterior compartment of the thigh. The areas of higher signal intensity (solid arrows) reveal enhancement after contrast material administration and do not show fat suppression, findings that result from intermixed hemorrhage and tumor. No definite areas of fat are seen, and the mass represents a nonspecific lesion because of these characteristics. (d) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) demonstrates a predominantly malignant fibrous histiocytoma pattern with scattered bizarre lipoblasts (arrowheads).

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 13b.  Pleomorphic liposarcoma of the thigh in a 47-year-old woman who presented with an enlarging thigh mass. (a–c) Axial T1-weighted MR images obtained before (500/8) (a) and after (600/8) (b) contrast enhancement and a T2-weighted MR image with fat suppression (4566/66) (c) reveal a large heterogeneous intramuscular and intermuscular mass (open arrows) in the posterior compartment of the thigh. The areas of higher signal intensity (solid arrows) reveal enhancement after contrast material administration and do not show fat suppression, findings that result from intermixed hemorrhage and tumor. No definite areas of fat are seen, and the mass represents a nonspecific lesion because of these characteristics. (d) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) demonstrates a predominantly malignant fibrous histiocytoma pattern with scattered bizarre lipoblasts (arrowheads).

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 13c.  Pleomorphic liposarcoma of the thigh in a 47-year-old woman who presented with an enlarging thigh mass. (a–c) Axial T1-weighted MR images obtained before (500/8) (a) and after (600/8) (b) contrast enhancement and a T2-weighted MR image with fat suppression (4566/66) (c) reveal a large heterogeneous intramuscular and intermuscular mass (open arrows) in the posterior compartment of the thigh. The areas of higher signal intensity (solid arrows) reveal enhancement after contrast material administration and do not show fat suppression, findings that result from intermixed hemorrhage and tumor. No definite areas of fat are seen, and the mass represents a nonspecific lesion because of these characteristics. (d) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) demonstrates a predominantly malignant fibrous histiocytoma pattern with scattered bizarre lipoblasts (arrowheads).

View larger version (172K): [in this window] [in a new window] [Download PPT slide]   Figure 13d.  Pleomorphic liposarcoma of the thigh in a 47-year-old woman who presented with an enlarging thigh mass. (a–c) Axial T1-weighted MR images obtained before (500/8) (a) and after (600/8) (b) contrast enhancement and a T2-weighted MR image with fat suppression (4566/66) (c) reveal a large heterogeneous intramuscular and intermuscular mass (open arrows) in the posterior compartment of the thigh. The areas of higher signal intensity (solid arrows) reveal enhancement after contrast material administration and do not show fat suppression, findings that result from intermixed hemorrhage and tumor. No definite areas of fat are seen, and the mass represents a nonspecific lesion because of these characteristics. (d) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) demonstrates a predominantly malignant fibrous histiocytoma pattern with scattered bizarre lipoblasts (arrowheads).

Pathologic Features
The gross pathologic appearance of pleomorphic liposarcoma is a large (median greatest diameter of 10 cm), multinodular, white to yellow mass. Myxoid and necrotic areas are common. These lesions represent high-grade sarcomas.

There are two distinguishable histologic types of pleomorphic liposarcomas, both of which demonstrate a high degree of cellular pleomorphism (8,82–84). The most common type is a malignant fibrous histiocytoma–like spindle cell tumor that may contain bizarre lipoblasts but often limited lipid-rich areas (Figs 12, 13). The second, less frequent variant is the epithelioid pleomorphic liposarcoma, which contains solid sheets of epithelioid-appearing cells and regions of fatty differentiation with bizarre lipoblasts (8). Pleomorphic liposarcomas do not show consistent cytogenetic aberrations (2,10).

Imaging Features
The radiographic appearance of pleomorphic liposarcoma is typically that of a nonspecific soft-tissue mass. US, CT, and MR imaging usually reveal a relatively well-defined mass, although infiltrative margins may also be seen (Figs 12, 13). Areas of necrosis and hemorrhage are frequent and account for the prominent heterogeneity seen in these lesions at cross-sectional imaging (7,12,41).

Compared with other types of liposarcoma, pleomorphic liposarcoma less frequently contains adipose tissue, reflecting the higher degree of anaplasia and grade of these lesions. This feature also makes the imaging diagnosis more difficult (Fig 12). Jelinek and co-workers (41) reported visible fat in pleomorphic liposarcoma in five of eight lesions (62%) at CT or MR imaging. In our experience, approximately 75% of lesions demonstrate foci of fat on MR images. These areas of adipose signal intensity are usually only small focal regions, compared with the overall tumor volume (Fig 12). The signal intensity of the adipose component may be slightly less than that of subcutaneous fat on T1-weighted MR images because of intermixed nonlipomatous malignant cells and volume averaging. As in cases of myxoid liposarcoma, the lipomatous elements in pleomorphic liposarcoma must be distinguished from hemorrhage, since both may demonstrate high signal intensity on T1-weighted MR images. On fat-suppressed T2-weighted images, the fat has low signal intensity, whereas blood shows high signal intensity (Figs 12, 13). In our experience, biopsy of these subtle adipose areas (as well as identification after surgical resection) may allow easier and more confident specific histologic diagnosis because more representative tissue is evaluated. The nonlipomatous areas have nonspecific features at CT (attenuation similar to that of muscle) and MR imaging (intermediate signal intensity with T1 weighting and intermediate to high signal intensity with T2 weighting).

Treatment and Prognosis
Pleomorphic liposarcoma is an aggressive, high-grade sarcoma with a marked propensity for tumor recurrence and metastatic disease. Multimodality therapy, combining chemotherapy, irradiation, and surgery, is often used for treatment of pleomorphic liposarcoma (2,4,7,8,10). The value of chemotherapy was confirmed in a recent study by Eilber and colleagues (85) in which ifosamide-based chemotherapy in patients with large, high-grade extremity liposarcomas was associated with an improved disease-specific survival rate, compared with the rate for patients who received no chemotherapy.

Advances in treatment have improved the prognosis for pleomorphic liposarcoma. A 5-year survival rate of only 21% was reported in 1962 by Enzinger and Winslow (11), but a recent study of a series of 57 patients with pleomorphic liposarcoma reported a higher 5-year survival rate of 63%, and local recurrence-free, metastasis-free, and disease-free survival rates were reported as 58%, 58%, and 39%, respectively (84). This study also showed (by multivariate analysis) that wide local excision or amputation and postoperative radiation therapy reduced local recurrence (84). In a follow-up analysis of pleomorphic liposarcomas, Gebhard and colleagues (82) found that the factors associated with a relatively poor prognosis were age greater than 60 years, nonextremity lesions, deep-seated tumor, and large tumor size (>5 cm in diameter). Metastases most frequently involve the lung, similar to the behavior of other high-grade sarcomas.

	Mixed-type Liposarcoma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
The mixed type of liposarcoma accounts for 5%–12% of all liposarcomas (2,10,12). It represents a combination of other subtypes. Mixed-type liposarcoma usually affects older patients, and common sites of involvement are the retroperitoneum and abdominal cavity (86). Other reported, but less commonly involved, locations are the mediastinum and extremities. The clinical, pathologic, and imaging features, as well as the treatment and prognosis of mixed-type liposarcoma, as expected, are a combination of the specific components of the lesion that have been previously discussed.

	Primary Liposarcoma of Bone

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Primary liposarcoma of bone is an exceedingly rare tumor, with a reported prevalence of 0.03% among all bone neoplasms (87). According to Mirra et al (87), males and females are affected equally, with patients ranging in age from 15 to 53 years (87). Liposarcoma of bone most commonly affects the long tubular bones, particularly the tibia, femur, and humerus (Fig 14) (9,87,88). Other rare sites of involvement include the scapula, maxilla, and mandible (1,89).

View larger version (168K): [in this window] [in a new window] [Download PPT slide]   Figure 14a.  Primary liposarcoma of bone in a 44-year-old woman with a 3-year history of knee pain, recently more severe. (a) Radiographs (anteroposterior and lateral) show an aggressive lytic lesion (*) with a wide zone of transition superiorly and cortical destruction anteriorly (arrows). Bone scan (not shown) revealed nonspecific marked increase in radiotracer accumulation. (b) CT scan reveals bone lysis with cortical permeation anteriorly into the soft tissues (arrows) without evidence of fat. (c–e) Axial T1-weighted MR images obtained before (660/20) (c) and after (640/ 20) (d) contrast enhancement and a coronal gradient echo T2* (420/25/30°) MR image (e) reveal an aggressive intraosseous lesion replacing bone marrow (*) and extending into the soft tissues (arrow). Small focus of fat (arrowhead) is seen on axial images. (f) Photograph of the coronally sectioned gross specimen demonstrates the destructive tibial lesion (open arrows), medial cortical permeation (solid arrow), and a small focus of fat (arrowhead) corresponding to the imaging findings.

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 14b.  Primary liposarcoma of bone in a 44-year-old woman with a 3-year history of knee pain, recently more severe. (a) Radiographs (anteroposterior and lateral) show an aggressive lytic lesion (*) with a wide zone of transition superiorly and cortical destruction anteriorly (arrows). Bone scan (not shown) revealed nonspecific marked increase in radiotracer accumulation. (b) CT scan reveals bone lysis with cortical permeation anteriorly into the soft tissues (arrows) without evidence of fat. (c–e) Axial T1-weighted MR images obtained before (660/20) (c) and after (640/ 20) (d) contrast enhancement and a coronal gradient echo T2* (420/25/30°) MR image (e) reveal an aggressive intraosseous lesion replacing bone marrow (*) and extending into the soft tissues (arrow). Small focus of fat (arrowhead) is seen on axial images. (f) Photograph of the coronally sectioned gross specimen demonstrates the destructive tibial lesion (open arrows), medial cortical permeation (solid arrow), and a small focus of fat (arrowhead) corresponding to the imaging findings.

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 14c.  Primary liposarcoma of bone in a 44-year-old woman with a 3-year history of knee pain, recently more severe. (a) Radiographs (anteroposterior and lateral) show an aggressive lytic lesion (*) with a wide zone of transition superiorly and cortical destruction anteriorly (arrows). Bone scan (not shown) revealed nonspecific marked increase in radiotracer accumulation. (b) CT scan reveals bone lysis with cortical permeation anteriorly into the soft tissues (arrows) without evidence of fat. (c–e) Axial T1-weighted MR images obtained before (660/20) (c) and after (640/ 20) (d) contrast enhancement and a coronal gradient echo T2* (420/25/30°) MR image (e) reveal an aggressive intraosseous lesion replacing bone marrow (*) and extending into the soft tissues (arrow). Small focus of fat (arrowhead) is seen on axial images. (f) Photograph of the coronally sectioned gross specimen demonstrates the destructive tibial lesion (open arrows), medial cortical permeation (solid arrow), and a small focus of fat (arrowhead) corresponding to the imaging findings.

View larger version (152K): [in this window] [in a new window] [Download PPT slide]   Figure 14d.  Primary liposarcoma of bone in a 44-year-old woman with a 3-year history of knee pain, recently more severe. (a) Radiographs (anteroposterior and lateral) show an aggressive lytic lesion (*) with a wide zone of transition superiorly and cortical destruction anteriorly (arrows). Bone scan (not shown) revealed nonspecific marked increase in radiotracer accumulation. (b) CT scan reveals bone lysis with cortical permeation anteriorly into the soft tissues (arrows) without evidence of fat. (c–e) Axial T1-weighted MR images obtained before (660/20) (c) and after (640/ 20) (d) contrast enhancement and a coronal gradient echo T2* (420/25/30°) MR image (e) reveal an aggressive intraosseous lesion replacing bone marrow (*) and extending into the soft tissues (arrow). Small focus of fat (arrowhead) is seen on axial images. (f) Photograph of the coronally sectioned gross specimen demonstrates the destructive tibial lesion (open arrows), medial cortical permeation (solid arrow), and a small focus of fat (arrowhead) corresponding to the imaging findings.

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 14e.  Primary liposarcoma of bone in a 44-year-old woman with a 3-year history of knee pain, recently more severe. (a) Radiographs (anteroposterior and lateral) show an aggressive lytic lesion (*) with a wide zone of transition superiorly and cortical destruction anteriorly (arrows). Bone scan (not shown) revealed nonspecific marked increase in radiotracer accumulation. (b) CT scan reveals bone lysis with cortical permeation anteriorly into the soft tissues (arrows) without evidence of fat. (c–e) Axial T1-weighted MR images obtained before (660/20) (c) and after (640/ 20) (d) contrast enhancement and a coronal gradient echo T2* (420/25/30°) MR image (e) reveal an aggressive intraosseous lesion replacing bone marrow (*) and extending into the soft tissues (arrow). Small focus of fat (arrowhead) is seen on axial images. (f) Photograph of the coronally sectioned gross specimen demonstrates the destructive tibial lesion (open arrows), medial cortical permeation (solid arrow), and a small focus of fat (arrowhead) corresponding to the imaging findings.

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 14f.  Primary liposarcoma of bone in a 44-year-old woman with a 3-year history of knee pain, recently more severe. (a) Radiographs (anteroposterior and lateral) show an aggressive lytic lesion (*) with a wide zone of transition superiorly and cortical destruction anteriorly (arrows). Bone scan (not shown) revealed nonspecific marked increase in radiotracer accumulation. (b) CT scan reveals bone lysis with cortical permeation anteriorly into the soft tissues (arrows) without evidence of fat. (c–e) Axial T1-weighted MR images obtained before (660/20) (c) and after (640/ 20) (d) contrast enhancement and a coronal gradient echo T2* (420/25/30°) MR image (e) reveal an aggressive intraosseous lesion replacing bone marrow (*) and extending into the soft tissues (arrow). Small focus of fat (arrowhead) is seen on axial images. (f) Photograph of the coronally sectioned gross specimen demonstrates the destructive tibial lesion (open arrows), medial cortical permeation (solid arrow), and a small focus of fat (arrowhead) corresponding to the imaging findings.

Wide surgical resection is the mainstay of treatment of primary osseous liposarcoma, with radiation therapy used for palliation or following excision to prevent local recurrence (9,87,88). The small number of cases in the literature makes assessment of prognosis unreliable. However, a mean survival rate of 2 years has been reported with osseous liposarcoma (87,88).

	Conclusions

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 
Liposarcoma is the second most common type of soft-tissue sarcoma. The radiologic manifestations of musculoskeletal liposarcoma have a wide spectrum and reflect their pathologic appearances. We have reviewed, illustrated, and correlated the pathologic and radiologic features of the histologic subtypes of soft-tissue liposarcoma, including well-differentiated, dedifferentiated, myxoid, pleomorphic, and mixed-type and the rare primary liposarcoma of bone. The unifying radiologic feature of these lesions, particularly at MR imaging, is the finding of adipose tissue in the vast majority of lesions. However, it is the radiologic appearance of associated nonlipomatous components and lesion location that often allows specific diagnosis of the subtypes of musculoskeletal liposarcomas. Imaging findings can be used to direct biopsy of representative regions from both the lipomatous and nonlipomatous components in these usually large neoplasms and lead to improved pathologic evaluation and a specific histologic diagnosis. Understanding and recognizing the spectrum of radiologic appearances and the pathologic basis of musculoskeletal liposarcoma allows improved patient assessment and is vital for optimal clinical management.

	Acknowledgments

 
The authors gratefully acknowledge the support of Anika Ismel Torruella for manuscript preparation. In addition, we thank the residents, without whom this project would not have been possible, who attend the Armed Forces Institute of Pathology’s radiologic pathology courses (past, present, and future) for their contribution to our series of patients.

	Footnotes

 
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official nor as reflecting the views of the Departments of the Army, Navy, or Defense.

	References

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Well-differentiated Liposarcoma Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Mixed-type Liposarcoma Primary Liposarcoma of Bone Conclusions References

 

1. Amarjit S, Bhardwaj DN, Nagpal BL. Intraosseous liposarcoma of the maxilla and mandible: report of two cases. J Oral Surg 1979;37:593–596.[Medline]
2. Christopher D, Unni K, Mertens F. Adipocytic tumors. In: WHO classification of tumors. Pathology and genetics: tumors of soft tissue and bone. Lyon, France: IARC, 2002; 19–46.
3. Fletcher D, Unni K, Mertens F. Liposarcoma of bone. In: World Health Organization classification of tumors. Pathology and genetics: tumors of soft tissue and bone. Lyon, France: IARC, 2002; 330.
4. Kempson R, Fletcher CD, Evans HL, Hendrickson MR, Sibley R. Malignant lipomatous tumors. In: Atlas of tumor pathology: tumor of the soft tissue. Washington, DC: Armed Forces Institute of Pathology, 2001; 217–238.
5. Kindblom LG, Angervall L, Svendsen P. Liposarcoma a clinicopathologic, radiographic and prognostic study. Acta Pathol Microbiol Scand Suppl 1975;253:1–71.
6. Kransdorf MJ. Malignant soft-tissue tumors in a large referral population: distribution of diagnoses by age, sex, and location. AJR Am J Roentgenol 1995;164:129–134.[Abstract/Free Full Text]
7. Kransdorf MJ, Murphey M. Liposarcoma. In: Imaging of soft tissue tumors. Philadelphia, Pa: Saunders, 1997; 79–98.
8. Miettinen M. Liposarcoma. In: Diagnostic soft tissue pathology. New York, NY: Churchill Livingstone, 2003; 227–240.
9. Resnick D. Tumors and tumor-like lesions of bone: imaging and pathology of specific lesions. In: Diagnosis of bone and joint disorders. 4th ed. Philadelphia, Pa: Saunders, 2002; 4152–4155.
10. Weiss S, Goldblum J. Liposarcoma. In: Enzinger and Weiss’s soft tissue tumors. 4th ed. St Louis, Mo: Mosby, 2001; 641–693.
11. Enzinger FM, Winslow DJ. Liposarcoma. A study of 103 cases. Virchows Arch Pathol Anat Physiol Klin Med 1962;335:367–388.[Medline]
12. Peterson JJ, Kransdorf MJ, Bancroft LW, O’Connor MI. Malignant fatty tumors: classification, clinical course, imaging appearance and treatment. Skeletal Radiol 2003;32:493–503.[CrossRef][Medline]
13. Evans HL. Liposarcoma: a study of 55 cases with a reassessment of its classification. Am J Surg Pathol 1979;3:507–523.[Medline]
14. Evans H. Liposarcomas and atypical lipomatous tumors: a study of 66 cases followed for a minimum of 10 years. Surg Pathol 1988;1:41–54.
15. Evans HL. Classification and grading of soft-tissue sarcomas. A comment. Hematol Oncol Clin North Am 1995;9:653–656.[Medline]
16. Weiss SW, Rao VK. Well-differentiated liposarcoma (atypical lipoma) of deep soft tissue of the extremities, retroperitoneum, and miscellaneous sites. A follow-up study of 92 cases with analysis of the incidence of "dedifferentiation." Am J Surg Pathol 1992;16:1051–1058.[Medline]
17. Dei Tos AP, Mentzel T, Newman PL, Fletcher CD. Spindle cell liposarcoma, a hitherto unrecognized variant of liposarcoma. Analysis of six cases. Am J Surg Pathol 1994;18:913–921.[Medline]
18. Enterline HT, Culberson JD, Rochlin DB, Brady LW. Liposarcoma. A clinical and pathological study of 53 cases. Cancer 1960;13:932–950.[CrossRef][Medline]
19. Evans HL, Soule EH, Winkelmann RK. Atypical lipoma, atypical intramuscular lipoma, and well differentiated retroperitoneal liposarcoma: a reappraisal of 30 cases formerly classified as well differentiated liposarcoma. Cancer 1979;43:574–584.[CrossRef][Medline]
20. Fanburg-Smith JC, Miettinen M. Liposarcoma with meningothelial-like whorls: a study of 17 cases of a distinctive histological pattern associated with dedifferentiated liposarcoma. Histopathology 1998;33:414–424.[CrossRef][Medline]
21. Hashimoto H, Daimaru Y, Enjoji M. S-100 protein distribution in liposarcoma. An immunoperoxidase study with special reference to the distinction of liposarcoma from myxoid malignant fibrous histiocytoma. Virchows Arch A Pathol Anat Histopathol 1984;405:1–10.[CrossRef][Medline]
22. Lazarus SS, Trombetta LD. Ultrastructural and histochemical identification of sclerosing liposarcoma. Histopathology 1981;5:223–235.[Medline]
23. Lucas DR, Nascimento AG, Sanjay BK, Rock MG. Well-differentiated liposarcoma. The Mayo Clinic experience with 58 cases. Am J Clin Pathol 1994;102:677–683.[Medline]
24. Reszel PA, Soule EH, Coventry MB. Liposarcoma of the extremities and limb girdles. A study of two hundred twenty-two cases. J Bone Joint Surg Am 1966;48:229–244.[Abstract/Free Full Text]
25. Eneroth M, Mandahl N, Heim S, et al. Localization of the chromosomal breakpoints of the t(12;16) in liposarcoma to subbands 12q13.3 and 16p11.2. Cancer Genet Cytogenet 1990;48:101–107.[CrossRef][Medline]
26. Goldblum JR, Frank T, Poy E, Weiss SW. pS3 mutations and tumor progression in well-differentiated liposarcoma and dermatofibrosaroma protuberant. Int J Surg Pathol 1995;3:35–42.
27. Gustafson P, Rydholm A, Willen H, Baldetorp B, Ferno M, Akerman M. Liposarcoma: a population-based epidemiologic and prognostic study of features of 43 patients, including tumor DNA content. Int J Cancer 1993;55:541–546.[Medline]
28. Rosner M, Yosepovich A, Paul M, Rosen N, Perelman M. Orbital well-differentiated liposarcoma demonstrating chromosomal imbalances. Eye 2005 Jan 28; [Epub ahead of print].
29. Sandberg AA. Updates on the cytogenetics and molecular genetics of bone and soft tissue tumors: liposarcoma. Cancer Genet Cytogenet 2004;155: 1–24.[CrossRef][Medline]
30. Fletcher CD, Akerman M, Dal Cin P, et al. Correlation between clinicopathological features and karyotype in lipomatous tumors. A report of 178 cases from the Chromosomes and Morphology (CHAMP) Collaborative Study Group. Am J Pathol 1996;148:623–630.[Abstract]
31. Rosai J, Akerman M, Dal Cin P, et al. Combined morphologic and karyotypic study of 59 atypical lipomatous tumors. Evaluation of their relationship and differential diagnosis with other adipose tissue tumors (a report of the CHAMP Study Group). Am J Surg Pathol 1996;20:1182–1189.[CrossRef][Medline]
32. Chew FS, Hudson TM. Radionuclide imaging of lipoma and liposarcoma. Radiology 1980;136: 741–745.[Abstract/Free Full Text]
33. Kransdorf MJ, Bancroft LW, Peterson JJ, Murphey MD, Foster WC, Temple HT. Imaging of fatty tumors: distinction of lipoma and well-differentiated liposarcoma. Radiology 2002;224:99–104.[Abstract/Free Full Text]
34. Behan M, Kazam E. The echographic characteristics of fatty tissues and tumors. Radiology 1978; 129:143–151.[Abstract]
35. Inampudi P, Jacobson JA, Fessell DP, et al. Soft-tissue lipomas: accuracy of sonography in diagnosis with pathologic correlation. Radiology 2004; 233:763–767.[Abstract/Free Full Text]
36. Ishida H, Naganuma H, Konno K, et al. Retroperitoneal liposarcoma: sonographic findings. Abdom Imaging 2000;25:554–558.[CrossRef][Medline]
37. Lin J, Jacobson JA, Fessell DP, Weadock WJ, Hayes CW. An illustrated tutorial of musculoskeletal sonography: part 4, musculoskeletal masses, sonographically guided interventions, and miscellaneous topics. AJR Am J Roentgenol 2000;175: 1711–1719.[Free Full Text]
38. Arkun R, Memis A, Akalin T, Ustun EE, Sabah D, Kandiloglu G. Liposarcoma of soft tissue: MRI findings with pathologic correlation. Skeletal Radiol 1997;26:167–172.[CrossRef][Medline]
39. Bush CH, Spanier SS, Gillespy T 3rd. Imaging of atypical lipomas of the extremities: report of three cases. Skeletal Radiol 1988;17:472–475.[CrossRef][Medline]
40. Hosono M, Kobayashi H, Fujimoto R, et al. Septum-like structures in lipoma and liposarcoma: MR imaging and pathologic correlation. Skeletal Radiol 1997;26:150–154.[CrossRef][Medline]
41. Jelinek JS, Kransdorf MJ, Shmookler BM, Aboulafia AJ, Malawer MM. Liposarcoma of the extremities: MR and CT findings in the histologic subtypes. Radiology 1993;186:455–459.[Abstract/Free Full Text]
42. Kransdorf MJ, Moser RP Jr, Meis JM, Meyer CA. Fat-containing soft-tissue masses of the extremities. RadioGraphics 1991;11:81–106.[Abstract]
43. Lindahl S, Markhede G, Berlin O. Computed tomography of lipomatous and myxoid tumors. Acta Radiol Diagn (Stockh) 1985;26:709–713.[Medline]
44. London J, Kim EE, Wallace S, Shirkhoda A, Coan J, Evans H. MR imaging of liposarcomas: correlation of MR features and histology. J Comput Assist Tomogr 1989;13:832–835.[Medline]
45. Munk PL, Lee MJ, Janzen DL, et al. Lipoma and liposarcoma: evaluation using CT and MR imaging. AJR Am J Roentgenol 1997;169:589–594.[Free Full Text]
46. Murphey MD, Carroll JF, Flemming DJ, Pope TL, Gannon FH, Kransdorf MJ. From the archives of the AFIP: benign musculoskeletal lipomatous lesions. RadioGraphics 2004;24:1433–1466.[Abstract/Free Full Text]
47. Ohguri T, Aoki T, Hisaoka M, et al. Differential diagnosis of benign peripheral lipoma from well-differentiated liposarcoma on MR imaging: is comparison of margins and internal characteristics useful? AJR Am J Roentgenol 2003;180:1689–1694.[Abstract/Free Full Text]
48. Yang YJ, Damron TA, Cohen H, Hojnowski L. Distinction of well-differentiated liposarcoma from lipoma in two patients with multiple well-differentiated fatty masses. Skeletal Radiol 2001; 30:584–589.[CrossRef][Medline]
49. Schwarzbach MH, Dimitrakopoulou-Strauss A, Mechtersheimer G, et al. Assessment of soft tissue lesions suspicious for liposarcoma by F18-deoxyglucose (FDG) positron emission tomography (PET). Anticancer Res 2001;21:3609–3614.[Medline]
50. Sampson CC, Saunders EH, Green WE, Laurey JR. Liposarcoma developing in a lipoma. Arch Pathol 1960;69:506–510.[Medline]
51. Sternberg SS. Liposarcoma arising within a subcutaneous lipoma. Cancer 1952;5:975–978.[CrossRef][Medline]
52. Wright C. Liposarcoma arising in a simple lipoma. J Pathol Bacteriol 1948;60:483–487.[CrossRef]
53. O’Connor M. Multimodality management of malignant soft-tissue tumors. In: Simon MA, Spring-field DS, eds. Surgery for bone and soft-tissue tumors. Philadelphia, Pa: Lippincott-Raven, 1998; 567–575.
54. O’Connor M. Surgical management of malignant soft-tissue tumors. In: Simon MA, Springfield DS, eds. Surgery for bone and soft-tissue tumors. Philadelphia, Pa: Lippincott-Raven, 1998; 555–565.
55. Azumi N, Curtis J, Kempson RL, Hendrickson MR. Atypical and malignant neoplasms showing lipomatous differentiation. A study of 111 cases. Am J Surg Pathol 1987;11:161–183.[CrossRef][Medline]
56. Edmonson JH, Petersen IA, Shives TC, et al. Chemotherapy, irradiation, and surgery for function-preserving therapy of primary extremity soft tissue sarcomas: initial treatment with ifosfamide, mitomycin, doxorubicin, and cisplatin plus granulocyte macrophage-colony-stimulating factor. Cancer 2002;94:786–792.[CrossRef][Medline]
57. Brooks JJ, Connor AM. Atypical lipoma of the extremities and peripheral soft tissues with dedifferentiation: implications for management. Surg Pathol 1990;3:169–178.
58. Hasegawa T, Seki K, Hasegawa F, et al. Dedifferentiated liposarcoma of retroperitoneum and mesentery: varied growth patterns and histological grades—a clinicopathologic study of 32 cases. Hum Pathol 2000;31:717–727.[CrossRef][Medline]
59. Henricks WH, Chu YC, Goldblum JR, Weiss SW. Dedifferentiated liposarcoma: a clinicopathological analysis of 155 cases with a proposal for an expanded definition of dedifferentiation. Am J Surg Pathol 1997;21:271–281.[CrossRef][Medline]
60. Kransdorf MJ, Meis JM, Jelinek JS. Dedifferentiated liposarcoma of the extremities: imaging findings in four patients. AJR Am J Roentgenol 1993; 161:127–130.[Abstract/Free Full Text]
61. McCormick D, Mentzel T, Beham A, Fletcher CD. Dedifferentiated liposarcoma. Clinicopathologic analysis of 32 cases suggesting a better prognostic subgroup among pleomorphic sarcomas. Am J Surg Pathol 1994;18:1213–1223.[Medline]
62. Meis JM. "Dedifferentiation" in bone and soft-tissue tumors. A histological indicator of tumor progression. Pathol Annu 1991;26(pt 1):37–62.
63. Yoshikawa H, Ueda T, Mori S, et al. Dedifferentiated liposarcoma of the subcutis. Am J Surg Pathol 1996;20:1525–1530.[CrossRef][Medline]
64. Snover DC, Sumner HW, Dehner LP. Variability of histologic pattern in recurrent soft tissue sarcomas originally diagnosed as liposarcoma. Cancer 1982;49:1005–1015.[CrossRef][Medline]
65. Ippolito V, Brien EW, Menendez LR, Mirra JM. Case report 797: "Dedifferentiated" lipoma-like liposarcoma of soft tissue with focal transformation to high-grade "sclerosing" osteosarcoma. Skeletal Radiol 1993;22:604–608.[Medline]
66. Kilpatrick SE, Doyon J, Choong PF, Sim FH, Nascimento AG. The clinicopathologic spectrum of myxoid and round cell liposarcoma. A study of 95 cases. Cancer 1996;77:1450–1458.[CrossRef][Medline]
67. Smith TA, Easley KA, Goldblum JR. Myxoid/ round cell liposarcoma of the extremities. A clinicopathologic study of 29 cases with particular attention to extent of round cell liposarcoma. Am J Surg Pathol 1996;20:171–180.[CrossRef][Medline]
68. Allen PW. Myxoid tumors of soft tissues. Pathol Annu 1980;15:133–192.[Medline]
69. Castleberry RP, Kelly DR, Wilson ER, Cain WS, Salter MR. Childhood liposarcoma. Report of a case and review of the literature. Cancer 1984;54: 579–584.[CrossRef][Medline]
70. La Quaglia MP, Spiro SA, Ghavimi F, Hajdu SI, Meyers P, Exelby PR. Liposarcoma in patients younger than or equal to 22 years of age. Cancer 1993;72:3114–3119.[CrossRef][Medline]
71. Shmookler BM, Enzinger FM. Liposarcoma occurring in children. An analysis of 17 cases and review of the literature. Cancer 1983;52:567–574.[CrossRef][Medline]
72. Dei Tos AP. Liposarcoma: new entities and evolving concepts. Ann Diagn Pathol 2000;4:252–266.[CrossRef][Medline]
73. Knight JC, Renwick PJ, Cin PD, Van den Berghe H, Fletcher CD. Translocation t(12;16)(q13;p11) in myxoid liposarcoma and round cell liposarcoma: molecular and cytogenetic analysis. Cancer Res 1995;55:24–27.[Abstract/Free Full Text]
74. Tuoheti Y, Okada K, Miyakoshi N, Nishida J, Itoi E. Unusual variant of liposarcoma with multiple punctate calcifications. Skeletal Radiol 2002;31: 666–670.[CrossRef][Medline]
75. Murphey M, Flemming D, Jelinek J, Temple H, Levine A, Torop A. Imaging of higher grade liposarcoma with pathologic correlation (abstr). Radiology 1997; 205(P):332.
76. Sung MS, Kang HS, Suh JS, et al. Myxoid liposarcoma: appearance at MR imaging with histologic correlation. RadioGraphics 2000;20:1007–1019.[Abstract/Free Full Text]
77. Ward EE, Jacobson JA, Fessell DP, Hayes CW, van Holsbeeck M. Sonographic detection of Baker’s cysts: comparison with MR imaging. AJR Am J Roentgenol 2001;176:373–380.[Abstract/Free Full Text]
78. Bancroft LW, Kransdorf MJ, Menke DM, O’Connor MI, Foster WC. Intramuscular myxoma: characteristic MR imaging features. AJR Am J Roentgenol 2002;178:1255–1259.[Abstract/Free Full Text]
79. Murphey MD, McRae GA, Fanburg-Smith JC, Temple HT, Levine AM, Aboulafia AJ. Imaging of soft-tissue myxoma with emphasis on CT and MR and comparison of radiologic and pathologic findings. Radiology 2002;225:215–224.[Abstract/Free Full Text]
80. Tateishi U, Hasegawa T, Beppu Y, Kawai A, Satake M, Moriyama N. Prognostic significance of MRI findings in patients with myxoid-round cell liposarcoma. AJR Am J Roentgenol 2004;182: 725–731.[Abstract/Free Full Text]
81. Pearlstone DB, Pisters PW, Bold RJ, et al. Patterns of recurrence in extremity liposarcoma: implications for staging and follow-up. Cancer 1999; 85:85–92.[CrossRef][Medline]
82. Gebhard S, Coindre JM, Michels JJ, et al. Pleomorphic liposarcoma: clinicopathologic, immunohistochemical, and follow-up analysis of 63 cases: a study from the French Federation of Cancer Centers Sarcoma Group. Am J Surg Pathol 2002; 26:601–616.[CrossRef][Medline]
83. Hornick JL, Bosenberg MW, Mentzel T, Mc-Menamin ME, Oliveira AM, Fletcher CD. Pleomorphic liposarcoma: clinicopathologic analysis of 57 cases. Am J Surg Pathol 2004;28:1257–1267.[Medline]
84. Oliveira AM, Nascimento AG. Pleomorphic liposarcoma. Semin Diagn Pathol 2001;18:274–285.[Medline]
85. Eilber FC, Eilber FR, Eckardt J, et al. The impact of chemotherapy on the survival of patients with high-grade primary extremity liposarcoma. Ann Surg 2004;240:686–695; discussion 695–697.[Medline]
86. Hisaoka M, Morimitsu Y, Hashimoto H, et al. Retroperitoneal liposarcoma with combined well-differentiated and myxoid malignant fibrous histiocytoma-like myxoid areas. Am J Surg Pathol 1999;23:1480–1492.[CrossRef][Medline]
87. Mirra JM, Picci P, Gold RH. Tumors of fat. In: Bone tumors: clinical, radiologic, and pathologic correlations. Philadelphia, Pa: Lea & Febiger, 1989; 1491–1494.
88. Schwartz A, Shuster M, Becker SM, Amboy P. Liposarcoma of bone. Report of a case and review of the literature. J Bone Joint Surg Am 1970;52: 171–177.[Abstract/Free Full Text]
89. Kenan S, Lewis MM, Abdelwahab IF, Hermann G, Klein MJ. Case report 652: primary intraosseous low grade myxoid sarcoma of the scapula (myxoid liposarcoma). Skeletal Radiol 1991;20: 73–75.[Medline]

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