DOI: 10.1148/rg.255055106
RadioGraphics 2005;25:1371-1395
From the Archives of the AFIP
Imaging of Musculoskeletal Liposarcoma with Radiologic-Pathologic Correlation1
Mark D. Murphey, MD,
Lynn K. Arcara, MD and
Julie Fanburg-Smith, MD
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).
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Abstract
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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.
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LEARNING OBJECTIVES FOR TEST 6
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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.
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Introduction
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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.
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Well-differentiated Liposarcoma
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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).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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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).
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The term atypical lipomatous tumor was introduced in 1979 by Evans and colleagues (13) as a replacement for well-differentiated liposarcoma to reflect its lack of metastatic potential more accurately. However, others have emphasized the variable use of the term atypical lipomatous tumor, which creates diagnostic confusion (10,12,14–16). The WHO Committee on Classification of Soft Tissue Tumors designated that these two terms are synonymous, since they describe lesions that are identical in morphology, karyotype, and biologic behavior (2). The WHO further suggested that the choice in terminology is "best determined by the degree of reciprocal comprehension between the surgeon and the pathologist to prevent either inadequate or excessive treatment" (2). We reserve the term atypical lipomatous lesion to describe only subcutaneous lesions (Fig 5) because of their limited morbidity and lack of significant potential for dedifferentiation. The term well-differentiated liposarcoma is used for all other lesions, because we believe the term atypical lipomatous tumor is inadequate to portray the significant morbidity, risk of dedifferentiation, and mortality associated with these lesions when they occur in other sites, particularly the retroperitoneum. It is important to emphasize that the choice of terminology is based entirely on lesion location and not on pathologic parameters.
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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.
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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.
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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.
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The clinical characteristics of well-differentiated liposarcoma are typically a painless, slow-growing (months to years) soft-tissue mass. Pain and tenderness have been reported in 10%–15% of cases (7,12). Retroperitoneal lesions often manifest with intraabdominal symptoms 5–10 years later than extremity lesions, owing to the difficulty in their detection (10). Lesions may be quite large at presentation, particularly retroperitoneal lesions, which may be greater than 20 cm in size (10).
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.
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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.
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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.
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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.
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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.
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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.
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At ultrasonography (US), a well-differentiated liposarcoma appears as a heterogeneous, multi-lobulated, typically well-defined mass. In our experience, sonographic identification of fat as hyperechogenicity is often difficult and variable in well-differentiated liposarcoma, similar to lipoma (34–37). The presence of hyperechoic foci suggests fat, but it is neither a sensitive nor specific finding, since it is seen in other lipomatous lesions. Thus, the ability to diagnose well-differentiated liposarcoma with US, compared with CT and MR imaging, is limited. Ishida et al (36) reported the identification of echogenic lines for diagnosis of retroperitoneal well-differentiated liposarcoma. However, as emphasized by these authors, this finding simply represents fine septa. In our opinion, fine septa are a nonspecific feature, which does not allow confident diagnosis of well-differentiated liposarcoma in the retroperitoneum or other anatomic locations.
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.
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Dedifferentiated Liposarcoma
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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).
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Abstract
LEARNING OBJECTIVES FOR TEST...
