DOI: 10.1148/rg.245045120
RadioGraphics 2004;24:1433-1466
From the Archives of the AFIP
Benign Musculoskeletal Lipomatous Lesions1
Mark D. Murphey, MD,
John F. Carroll, MD,
Donald J. Flemming, CAPT, MC, USN,
Thomas L. Pope, MD,
Francis H. Gannon, MD and
Mark J. Kransdorf, MD
1 From the Departments of Radiologic Pathology (M.D.M., J.F.C., T.L.P.) and Orthopedic Pathology (F.H.G.), Armed Forces Institute of Pathology, 6825 16th St NW, Bldg 54, Rm M-133A, Washington, DC 20306; Department of Radiology, Medical University of South Carolina, Charleston (T.L.P.); Departments of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, Md (M.D.M., D.J.F.); Department of Radiology, University of Maryland School of Medicine, Baltimore (M.D.M.); Department of Radiology, National Naval Medical Center, Bethesda, Md (D.J.F.); and Department of Radiology, Mayo Clinic, Jacksonville, Fla (M.J.K.). Received June 1, 2004; revision requested June 7 and received June 24; accepted June 24. All authors have no financial relationships to disclose. Address correspondence to M.D.M. (e-mail: murphey@afip.osd.mil).
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Abstract
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Benign lipomatous lesions involving soft tissue are common musculoskeletal masses that are classified into nine distinct diagnoses: lipoma, lipomatosis, lipomatosis of nerve, lipoblastoma or lipoblastomatosis, angiolipoma, myolipoma of soft tissue, chondroid lipoma, spindle cell lipoma and pleomorphic lipoma, and hibernoma. Soft-tissue lipoma accounts for almost 50% of all soft-tissue tumors. Radiologic evaluation is diagnostic in up to 71% of cases. These lesions are identical to subcutaneous fat on computed tomographic (CT) and magnetic resonance (MR) images and may contain thin septa. Lipomatosis represents a diffuse overgrowth of mature fat affecting either subcutaneous tissue, muscle or nerve, and imaging is needed to evaluate lesion extent. Lipoblastoma is a tumor of immature fat occurring in young children, and imaging features may reveal a mixture of fat and nonadipose tissue. Angiolipoma, myolipoma, and chondroid lipoma are rare lipomatous lesions that are infrequently imaged. Spindle cell and pleomorphic lipoma appear as a subcutaneous lipomatous mass in the posterior neck or shoulder, with frequent nonadipose components. Hibernoma appears as a lipomatous mass with serpentine vascular elements. Benign lipomatous lesions affecting bone, joint, or tendon sheath include intraosseous lipoma, parosteal lipoma, liposclerosing myxofibrous tumor, discrete lipoma of joint or tendon sheath, and lipoma arborescens. Intraosseous and parosteal lipoma have a pathognomonic CT or MR appearance, with fat in the marrow space or on the bone surface, respectively. Liposclerosing myxofibrous tumor is a rare intermixed histologic lesion commonly located in the medullary canal of the intertrochanteric femur. Benign lipomatous lesions may occur focally in a joint or tendon sheath or with diffuse villonodular proliferation in the synovium (lipoma arborescens) and are diagnosed based on location and identification of fat. Understanding the spectrum of appearances of the various benign musculoskeletal lipomatous lesions improves radiologic assessment and is vital for optimal patient management.
Index Terms: Bone neoplasms, 40.363 • Lipoma and lipomatosis, 40.363 • Soft tissues, neoplasms, 40.363
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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:
- List the radiologic spectrum of benign musculoskeletal lipomatous lesions.
- Recognize the pathologic basis of the radiologic features of benign musculoskeletal lipomatous lesions.
- Identify the radiologic manifestations that may allow differentiation of the various benign musculoskeletal lipomatous lesions and the implications for diagnosis and treatment.
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Introduction
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Benign musculoskeletal lipomatous lesions are common in both soft tissue and bone. Benign lipomatous lesions involving the soft tissues have been recently categorized by the World Health Organization’s Committee for the Classification of Soft Tissue Tumors in 2002 (1) into nine entities, including lipoma, lipomatosis, lipomatosis of nerve, lipoblastoma/lipoblastomatosis, angiolipoma, myolipoma of soft tissue, chondroid lipoma, spindle cell/pleomorphic lipoma, and hibernoma. Benign lipomatous lesions affecting bone include intraosseous lipoma, parosteal lipoma, and liposclerosing myxofibrous tumor (LSMFT). Benign lipomatous lesions may also affect joints and tendon sheaths either focally or more commonly diffusely (lipoma arborescens).
Imaging features of benign lipomatous lesions are often pathognomonic. Radiologic evaluation frequently reveals tissue with either diffuse or focal areas that are similar or identical to subcutaneous fat. These intrinsic features and lesion extent are best depicted with either computed tomography (CT) or magnetic resonance (MR) imaging. In this article, the clinical characteristics, pathologic features, spectrum of radiologic appearances, and treatment for the various types of benign musculoskeletal lipomatous lesions are discussed and illustrated.
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Soft-tissue Lipomatous Lesions
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Lipoma
The lipoma represents the most common soft-tissue neoplasm, accounting for almost 50% of all soft-tissue tumors in the largest series to date by Myhre-Jensen (2) of 1331 lesions. The prevalence of soft-tissue lipoma has been estimated at 2.1 per 100 people (2–5). Lipomas are much more frequent than liposarcoma by an estimated ratio of 100:1 (2–5). It is unclear if a soft-tissue lipoma represents a benign neoplasm, a local hyperplasia of fat cells, or a combination of both processes. Soft-tissue lipomas can be categorized as superficial or deep. Superficial lipomas are subcutaneous and are extraordinarily common lesions, accounting for 16%–50% (2,3) of all soft-tissue tumors in several large series (Fig 1). These lesions most frequently affect the upper back, neck, proximal extremities (particularly the shoulder), and abdomen. Lipomas most commonly occur in the 5th to 7th decades of life, with 80% of lesions found in patients 27–85 years of age (2,3). There is no clear gender predilection. Superficial lipomas are smaller than 5 cm in 80% of cases, with only 1% of lesions greater than 10 cm in size (3).
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Figure 1a. Subcutaneous lipoma superior to the clavicle in a 32-year-old woman. (a, b) Coronal T1-weighted (repetition time msec/echo time msec= 583/30) (a) and T2-weighted (2580/80) (b) MR images show a mass that is isointense relative to subcutaneous fat (*). It is surrounded by a low-signal-intensity capsule (arrows), which allows it to be distinguished from adjacent adipose tissue. (c) Photograph of the sectioned gross specimen reveals diffuse fat throughout the lesion (*) and the surrounding capsule (arrowheads).
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Figure 1b. Subcutaneous lipoma superior to the clavicle in a 32-year-old woman. (a, b) Coronal T1-weighted (repetition time msec/echo time msec= 583/30) (a) and T2-weighted (2580/80) (b) MR images show a mass that is isointense relative to subcutaneous fat (*). It is surrounded by a low-signal-intensity capsule (arrows), which allows it to be distinguished from adjacent adipose tissue. (c) Photograph of the sectioned gross specimen reveals diffuse fat throughout the lesion (*) and the surrounding capsule (arrowheads).
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Figure 1c. Subcutaneous lipoma superior to the clavicle in a 32-year-old woman. (a, b) Coronal T1-weighted (repetition time msec/echo time msec= 583/30) (a) and T2-weighted (2580/80) (b) MR images show a mass that is isointense relative to subcutaneous fat (*). It is surrounded by a low-signal-intensity capsule (arrows), which allows it to be distinguished from adjacent adipose tissue. (c) Photograph of the sectioned gross specimen reveals diffuse fat throughout the lesion (*) and the surrounding capsule (arrowheads).
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Deep lipomas are less common than their superficial counterparts. Although the study by Myhre-Jensen (2) showed only 1%–2% of lesions as being deep-seated, we believe these lesions have a much higher prevalence. This discrepancy may be partially related to the fact that many superficial lesions are not imaged and only evaluated clinically. Weiss and Goldblum (6) separate deep lipomas from lesions in an intramuscular or intermuscular location. We believe this division is arbitrary and confusing at best and consider all lipomas beneath the superficial fascia as deep-seated lesions. Deep lipomas in the chest wall, hands, feet, and retroperitoneum are rare (approximately 1% of lipomas) (2,3). In fact, a lipomatous lesion in a retroperitoneal location should be considered a well-differentiated liposarcoma because of the rarity of lipoma in this location (5,7). Deep lipoma involving the extremities is most commonly intramuscular (Fig 2). Lesions may also be primarily intermuscular in location. The large size of these deep lipomas is often associated with involvement of both intra- and intermuscular tissues, and the term infiltrating lipoma has been applied to these lesions (Fig 2) (8). Deep soft-tissue lipomas most frequently occur in patients 30–60 years old, and lesions commonly affect the large muscle groups of the lower extremity (45% of cases), trunk (17%), shoulder (12%), and upper extremity (10%) (2,3,9). There is a general consensus that men are affected more frequently than are women. Although the size range at manifestation is wide, from small to 20 cm, deep lipomas are larger than their superficial counterparts at clinical presentation (2,3,9).
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Figure 2a. Deep infiltrating intramuscular lipoma of the calf in a 17-year-old boy with a palpable soft-tissue mass. (a) Axial T1-weighted (600/12) MR image shows a mass isointense relative to subcutaneous fat that infiltrates the soleus muscle (arrows) and extends across the intermuscular planes to more mildly involve other calf muscles (arrowheads). (b) Photograph of the axially sectioned gross specimen reveals infiltrating lipoma (black *) extensively interdigitating with the soleus muscle (white *).
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Figure 2b. Deep infiltrating intramuscular lipoma of the calf in a 17-year-old boy with a palpable soft-tissue mass. (a) Axial T1-weighted (600/12) MR image shows a mass isointense relative to subcutaneous fat that infiltrates the soleus muscle (arrows) and extends across the intermuscular planes to more mildly involve other calf muscles (arrowheads). (b) Photograph of the axially sectioned gross specimen reveals infiltrating lipoma (black *) extensively interdigitating with the soleus muscle (white *).
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A lipoma typically manifests as a discrete mobile palpable doughy, solitary soft-tissue mass. Lesions are frequently otherwise asymptomatic and may enlarge slowly. Associated clinical symptoms are uncommon but include local pain, tenderness, limitation of range of motion, and nerve compression and are reported in approximately 25% of patients with superficial lipomas (8). Clinical evaluation of superficial lipomas is accurate for diagnosis in up to 85% of cases (2,3,10). This frequency of clinically determined diagnosis is in contradistinction to deep lipomas for which clinical evaluation indicates only a nonspecific mass. Such nonspecific findings account for the more frequent imaging of deep-seated lesions, as previously mentioned. Several additional interesting clinical features have been reported. A diagnostic criterion used by some clinicians for superficial lesions is hardening of the mass after application of ice. Lipomas may also increase in size during periods of rapid weight gain. The fat in lipomas is considered unavailable for general metabolism as evidenced by the stable size of lesions during periods of severe weight loss, at which time lesions may become more apparent. Deep lesions may also become more apparent as distinct masses with muscle contraction.
Lipomas are estimated to be multiple in 5%–15% of patients (2,3,10–12). Patients with multiple lesions tend to be male (6.6:1) (2,3,10–12). Multiple lipomas predominate in the back, shoulder, and upper arms; may be symmetric; show a predilection for the extensor surface; and are most common in the 5th to 6th decades of life. Multiple lipomas are familial in approximately 30% of cases, with inheritance reported to be both autosomal dominant and recessive but likely polygenic (13–15). Patients with familial multiple lipomas also tend to be male, with lesions located superficially in the forearms, trunk, thighs, and arms. There are no known metabolic abnormalities associated with familial multiple lipomas, and patients are generally affected in the 3rd to 4th decades of life. The number of lesions varies from only a few to several hundred (6). Clinical symptoms are usually limited to disfigurement, although there has been a report of peripheral neuropathy with familial multiple lipomas. The asymmetric distribution and focal encapsulation of these lesions aid in distinguishing them from lipomatosis. Several entities associated with multiple lipomas include Bannayan-Zonana syndrome, Cowden syndromes, Fröhlich syndrome, and Proteus syndrome.
A lipoma is composed of mature adipocytes and uniform nuclei that are identical to those seen in normal adult (white) fat. At gross examination, soft-tissue lipomas are well-circumscribed lesions with a greasy consistency and yellow to orange color. A thin capsule delineates the lipoma from the surrounding tissue. The adipose cells are often slightly larger than normal adipocytes. Although the vascular supply network to lipomas is rich, it is inconspicuous because of compression by the distended lipocytes (4,6). Deep lesions may show microscopic infiltration of surrounding musculature. Additional mesenchymal elements are occasionally apparent. The most frequent nonlipomatous component is fibrous connective tissue that often predominates in septa. Prominent nonseptal fibrous components may also occur, and such lesions may be referred to as fibrolipomas. Other mesenchymal elements that may be seen include bone and cartilage.
Cytogenetic abnormalities have been found in 50%–80% of lipomas (1,6,16). Three major subgroups of genetic aberrations have been identified, including 12q13–15, 6p21–23, and deletions from q13 (1,6,16). The 12q13–15 genetic aberration is most frequent, accounting for two-thirds of lipomas with abnormal karyotypes (1,6,16). The HMGIC gene located in 12q15 is specifically affected and is a member of the high-mobility group proteins family, with overexpression implicated as playing an important role in lipoma origin (1,6,16). The lesions in patients with familial multiple lipomas show similar genetic abnormalities as well as translocation on chromosome 3 (lipoma preferred partner gene) (13–15).
At radiography, small lipomas often appear normal. Larger lipomas may reveal typical radiolucency (Fig 3). Underlying osseous abnormalities are rare. Mineralization is unusual but has been reported, both chondroid and osteoid, in up to 11% of cases (11,12,17).
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Figure 3a. Deep intramuscular lipoma of the thigh in a 64-year-old woman with a slowly enlarging soft-tissue mass. (a) Radiograph of the proximal thigh shows a radiolucent soft-tissue mass (arrows). (b) CT scan reveals the low-attenuation lipomatous mass (*) with thin septa (arrowheads) in the anterior compartment of the thigh. (c, d) Axial T1-weighted (500/17) (c) and T2-weighted (2100/90) (d) MR images reveal a mass that is isointense relative to subcutaneous fat with both pulse sequences (*) and that contains thin delicate septa (arrows), which remain predominantly low signal intensity on the long TR image (d). (e) Photograph of the axially sectioned gross specimen demonstrates the lipomatous mass (*) with thin septa (arrowheads).
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Figure 3b. Deep intramuscular lipoma of the thigh in a 64-year-old woman with a slowly enlarging soft-tissue mass. (a) Radiograph of the proximal thigh shows a radiolucent soft-tissue mass (arrows). (b) CT scan reveals the low-attenuation lipomatous mass (*) with thin septa (arrowheads) in the anterior compartment of the thigh. (c, d) Axial T1-weighted (500/17) (c) and T2-weighted (2100/90) (d) MR images reveal a mass that is isointense relative to subcutaneous fat with both pulse sequences (*) and that contains thin delicate septa (arrows), which remain predominantly low signal intensity on the long TR image (d). (e) Photograph of the axially sectioned gross specimen demonstrates the lipomatous mass (*) with thin septa (arrowheads).
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Figure 3c. Deep intramuscular lipoma of the thigh in a 64-year-old woman with a slowly enlarging soft-tissue mass. (a) Radiograph of the proximal thigh shows a radiolucent soft-tissue mass (arrows). (b) CT scan reveals the low-attenuation lipomatous mass (*) with thin septa (arrowheads) in the anterior compartment of the thigh. (c, d) Axial T1-weighted (500/17) (c) and T2-weighted (2100/90) (d) MR images reveal a mass that is isointense relative to subcutaneous fat with both pulse sequences (*) and that contains thin delicate septa (arrows), which remain predominantly low signal intensity on the long TR image (d). (e) Photograph of the axially sectioned gross specimen demonstrates the lipomatous mass (*) with thin septa (arrowheads).
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Figure 3d. Deep intramuscular lipoma of the thigh in a 64-year-old woman with a slowly enlarging soft-tissue mass. (a) Radiograph of the proximal thigh shows a radiolucent soft-tissue mass (arrows). (b) CT scan reveals the low-attenuation lipomatous mass (*) with thin septa (arrowheads) in the anterior compartment of the thigh. (c, d) Axial T1-weighted (500/17) (c) and T2-weighted (2100/90) (d) MR images reveal a mass that is isointense relative to subcutaneous fat with both pulse sequences (*) and that contains thin delicate septa (arrows), which remain predominantly low signal intensity on the long TR image (d). (e) Photograph of the axially sectioned gross specimen demonstrates the lipomatous mass (*) with thin septa (arrowheads).
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Figure 3e. Deep intramuscular lipoma of the thigh in a 64-year-old woman with a slowly enlarging soft-tissue mass. (a) Radiograph of the proximal thigh shows a radiolucent soft-tissue mass (arrows). (b) CT scan reveals the low-attenuation lipomatous mass (*) with thin septa (arrowheads) in the anterior compartment of the thigh. (c, d) Axial T1-weighted (500/17) (c) and T2-weighted (2100/90) (d) MR images reveal a mass that is isointense relative to subcutaneous fat with both pulse sequences (*) and that contains thin delicate septa (arrows), which remain predominantly low signal intensity on the long TR image (d). (e) Photograph of the axially sectioned gross specimen demonstrates the lipomatous mass (*) with thin septa (arrowheads).
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The sonographic appearance of a lipoma is that of a hyperechoic mass (11,18). This intrinsic echogenicity makes distinction of the echogenic capsule difficult. No posterior acoustic enhancement is seen. Heterogeneity caused by septa or other nonlipomatous components may be identified. Although the hyperechoic appearance suggests fat, in our experience CT or MR imaging is significantly superior for the confident identification of adipose tissue in these lesions.
CT and MR imaging of soft-tissue lipoma reveal a mass of homogeneous adipose tissue in 11%–22% of cases (Figs 1, 2) (12,17,19–21). Hounsfield unit measurements of soft-tissue lipoma are usually between –65 and –120, although the value varies by specific body location and direct comparison with the attenuation of surrounding normal fat is often helpful (17,20). MR images of these lesions reveals tissue that is isointense relative to subcutaneous fat, regardless of pulse sequence. We believe that the percentage of lipomas with this CT or MR imaging appearance in routine clinical practice likely approaches 50% (which is much higher than the stated 11%–22%), because the more complicated cases are referred to academic tertiary case centers. These cases in which the entire lesion is composed of only adipose tissue allow a confident diagnosis of lipoma at CT or MR imaging, because well-differentiated liposarcomas do not demonstrate this homogeneous appearance. No contrast material enhancement is seen at CT or MR imaging in this group of lipomas, except of the fibrous capsule (17,20).
Lipomas frequently (37%–49% of cases) demonstrate intrinsic thin septa (<2 mm) on CT or MR images (Fig 3) (12,17,19–22). The detection of only thin delicate septa, particularly when few in number, also allows confident diagnosis of soft-tissue lipoma (23–28). Well-differentiated liposarcoma have this feature only rarely (4%–9% of cases) and generally not in deep-seated lesions (17,20). In addition, Ohguri et al (20) showed that the septal enhancement pattern on contrast material–enhanced MR images may be helpful in distinguishing lipoma from well-differentiated liposarcoma. In their study, 58% of lipomas with septa showed no enhancement and 37% revealed moderate enhancement (20). Well-differentiated liposarcomas showed moderate (25%) to marked (75%) enhancement of the septa in all cases (20). These researchers did not report differences in enhancement between lesions with thin (<2 mm) versus thick (>2 mm) septa (20). We believe that a soft-tissue lipomatous lesion with only thin septa that do not enhance at MR imaging can be confidently diagnosed as a lipoma.
Soft-tissue lipomas may have a more complex appearance with significant nonadipose elements. On CT and MR images, these foci may include thick septa (>2 mm) as well as nodular or globular regions of nonadipose tissue (reported in 28%–31% of cases) (Fig 4) (12,17,19–21). Such lipomas cannot be distinguished from well-differentiated liposarcoma with imaging alone. We suggest biopsy directed at these nonadipose regions, particularly if nodular or globular, both to diagnose well-differentiated liposarcoma and also to exclude the possibility of dedifferentiation (29). In lipomas, these nonadipose regions correspond to previously described mesenchymal elements or areas of fat necrosis.
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Figure 4a. Deep intramuscular lipoma with thick septa in a 60-year-old woman with a slowly enlarging mass in the thigh. (a, b) Coronal T1-weighted (600/30) (a) and T2-weighted (2000/90) (b) MR images show a heterogeneous mass (*) that is predominantly isointense relative to subcutaneous fat. However, prominent thick septations with some nodularity are also present (arrowheads), some of which reveal high signal intensity on the long TR image (b). These features do not allow distinction from well-differentiated liposarcoma. (c) Photograph of the longitudinally sectioned gross specimen demonstrates the lipomatous tissue (*) with thick septa and focal nodularity (arrows).
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Figure 4b. Deep intramuscular lipoma with thick septa in a 60-year-old woman with a slowly enlarging mass in the thigh. (a, b) Coronal T1-weighted (600/30) (a) and T2-weighted (2000/90) (b) MR images show a heterogeneous mass (*) that is predominantly isointense relative to subcutaneous fat. However, prominent thick septations with some nodularity are also present (arrowheads), some of which reveal high signal intensity on the long TR image (b). These features do not allow distinction from well-differentiated liposarcoma. (c) Photograph of the longitudinally sectioned gross specimen demonstrates the lipomatous tissue (*) with thick septa and focal nodularity (arrows).
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Figure 4c. Deep intramuscular lipoma with thick septa in a 60-year-old woman with a slowly enlarging mass in the thigh. (a, b) Coronal T1-weighted (600/30) (a) and T2-weighted (2000/90) (b) MR images show a heterogeneous mass (*) that is predominantly isointense relative to subcutaneous fat. However, prominent thick septations with some nodularity are also present (arrowheads), some of which reveal high signal intensity on the long TR image (b). These features do not allow distinction from well-differentiated liposarcoma. (c) Photograph of the longitudinally sectioned gross specimen demonstrates the lipomatous tissue (*) with thick septa and focal nodularity (arrows).
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Several additional imaging features of soft-tissue lipomas deserve discussion. Areas of mineralization may be apparent (best seen with CT), but they are more frequently associated with well-differentiated liposarcoma. Subcutaneous and intermuscular lipomas frequently demonstrate a fibrous capsule with attenuation similar to that of muscle at CT and low signal intensity on all MR images regardless of pulse sequence. This capsule is not seen with intramuscular lesions, as it cannot be distinguished from the surrounding muscle. Intramuscular lipomas may also demonstrate irregular margins and interdigitations with skeletal muscle that create a striated appearance (Fig 2) (8,11). This feature has not been described with liposarcoma and allows confident diagnosis of intramuscular lipoma. Intermuscular lipomas, particularly those centered in the popliteal or inguinal region, may encase the neurovascular bundle. This feature limits the ability to perform complete resection and increases the likelihood of local recurrence. Finally, subcutaneous lipomas may not show a surrounding capsule at CT or MR imaging (Fig 5). These lesions have recently been referred to as nonencapsulated lipomas and may be difficult to detect as distinct masses because they blend imperceptibly with the surrounding subcutaneous fat (30). These lesions emphasize the importance of placing a marker over the palpable mass, clinical correlation, and occasional necessity of comparison with the contralateral side to detect significant asymmetry. A low-signal-intensity capsule may be difficult to detect because it is incomplete, it is too thin to resolve, or a nonoptimal imaging plane or section thickness was used. The study by Roberts and colleagues (30) suggested that 54% of subcutaneous lipomas lacked a capsule, although these imaging findings were surgically confirmed in only one of these lesions. We believe that the prevalence of nonencapsulated lipomas is much lower than this percentage.
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Figure 5a. Unencapsulated subcutaneous lipoma in a 40-year old man. (a) Axial T1-weighted MR image (545/16.5) shows a mass (*) with signal intensity identical to that of subcutaneous fat and that blends imperceptibly with surrounding adipose tissue. No low-signal-intensity capsule is seen separating the lipoma from the subcutaneous fat. Note the anterior marker in place for identifying this as the site of a palpable soft-tissue mass. (b) Photomicrograph (original magnification, x175; hematoxylin-eosin [H-E] stain) reveals typical large adipocytes that composed the entire lesion.
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Figure 5b. Unencapsulated subcutaneous lipoma in a 40-year old man. (a) Axial T1-weighted MR image (545/16.5) shows a mass (*) with signal intensity identical to that of subcutaneous fat and that blends imperceptibly with surrounding adipose tissue. No low-signal-intensity capsule is seen separating the lipoma from the subcutaneous fat. Note the anterior marker in place for identifying this as the site of a palpable soft-tissue mass. (b) Photomicrograph (original magnification, x175; hematoxylin-eosin [H-E] stain) reveals typical large adipocytes that composed the entire lesion.
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Treatment of soft-tissue lipoma depends on tumor location, size, and clinical symptoms referable to the lesion. Most superficial lipomas are asymptomatic and do not require treatment or surgical excision. Symptomatic, large or deep lipomas are often surgically excised with a wide resection, including the capsule and a small cuff of surrounding tissue. The prevalence of local recurrence has been estimated at 4%–5% and is more frequent with deep and infiltrating lesions (1,2,6). Resection of large and deep lesions is more difficult, and the extent of resection is often modified to avoid injuring nearby important neurovascular or muscular tissue and causing functional impairment. This compromise between adequate surgical margins and functional disability may lead to incomplete resection and an obviously higher local recurrence rate. MR imaging is optimal for detecting local recurrence of lipomas, as with other soft-tissue neoplasms. However, it is important to understand that these benign lesions have no metastatic potential. In addition, malignant transformation has only very rarely been reported (31–33). In fact, we believe malignant transformation is nonexistent and that reported rare cases likely represent sampling errors or misdiagnosis at initial investigation.
Lipomatosis
Lipomatosis represents a diffuse overgrowth of mature adipose tissue. Multiple types of lipomatosis typically differentiated by anatomic location and varying clinical manifestations have been described. These include multiple symmetric lipomatosis, infiltrating congenital lipomatosis of the face, encephalocraniocutaneous lipomatosis, shoulder girdle lipomatosis, adipose dolorosa, pelvic lipomatosis, and mediastinal lipomatosis. We limit our discussion to those lesions primarily involving the muscular and subcutaneous tissue. Extensive involvement of both muscle and subcutaneous tissue typically differentiates a large intermuscular or intramuscular lipoma from lipomatosis. Osseous overgrowth is not as common as is seen with lipomatosis of nerves (with macrodystrophia lipomatosa), and no nerve involvement by the adipose tissue is present in lipomatosis.
Patients with lipomatosis are affected at a much younger age than those with solitary soft-tissue lipomas, usually by the age of 2 years (11). There are rare reports of presentation in adulthood. Clinical features of lipomatosis are a direct result of the massive diffuse accumulation of fat in the affected anatomic locations. Pathologic analysis reveals aggregates of adult type fat that are poorly circumscribed and infiltrative. Imaging of lipomatosis demonstrates the infiltrative pattern of fat overgrowth that affects both the subcutaneous and deep soft tissues.
Brodie originally described multiple symmetric lipomatosis in 1846 (34). Madelung was the first to extensively describe this entity in a series of patients in 1888, and the disease is frequently referred to as Madelung disease (35). Launois and Bensaude reported 65 cases in 1889, further describing this condition, which has also been referred to as Launois-Bensaude syndrome (36). Currently, more than 270 cases have been reported. Multiple symmetric lipomatosis almost exclusively affects middle-aged men and shows a high association with alcoholism (60%–90% of cases) (34,37–45). There is an increased prevalence among patients of Mediterranean descent, and an autosomal dominant inheritance has been suggested. The cause of this disease is not known, although numerous metabolic abnormalities (hyperuricemia, gout, hyperlipidemia, and diabetes) have been inconsistently associated with the disease. Point mutations for mitochondria DNA (codon 8344), which are important in alcohol metabolism, have been detected in 28% of patients (42). Alcohol abuse may then lead to promotion of fat production. The painless, progressive fat deposition occurs insidiously, primarily affecting the neck and upper trunk, arms, cheeks, and axilla. This deposition in the neck frequently causes a donut-shaped collar of fat (lipoma annulare colli). Sensorimotor neuropathies are common (59%–84% of patients), with 50% showing central nervous system involvement (46). Imaging, particularly CT and MR, reveals these infiltrative fatty masses typically in a subcutaneous distribution but more frequently between the deep muscles (sternocleidomastoid, trapezius, and paraspinal) (11,42,44,45,47) (Fig 6). Rare extension into the mediastinum may cause tracheal narrowing, which can be depicted with CT. Treatment of multiple symmetric lipomatosis is often performed for cosmesis. Conservative surgical resection and liposuction have proved effective, although these therapies may be unnecessary as abstinence from alcohol or correction of metabolic disturbances may arrest further progression.
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Figure 6a. Multiple symmetric lipomatosis in a 45-year-old man. (a) CT scan shows diffuse infiltration of fat between the lumbar paraspinal muscles (arrows), as well as infiltration of the left anterior abdominal wall musculature (*). (b) Photomicrograph (original magnification, x150; H-E stain) reveals lipomatous tissue (L) infiltrating muscle bundles (M).
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Figure 6b. Multiple symmetric lipomatosis in a 45-year-old man. (a) CT scan shows diffuse infiltration of fat between the lumbar paraspinal muscles (arrows), as well as infiltration of the left anterior abdominal wall musculature (*). (b) Photomicrograph (original magnification, x150; H-E stain) reveals lipomatous tissue (L) infiltrating muscle bundles (M).
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Infiltrating congenital lipomatosis of the face was described by Slavin et al in 1983 (48). As the name implies, this lesion consists of infiltrative nonencapsulated tumor composed of benign mature adult fat typically limited to the cheek and face. Lesion growth may lead to facial asymmetry, parotid involvement, osseous hypertrophy, and macroglossia and may be associated with cutaneous capillary blush and mucosal neuromas. Treatment is complicated by compromise between early resection that limits extensive infiltration and the number of surgical procedures needed versus the higher likelihood of facial nerve damage in younger patients (49,50). Liposuction is an additional method employed to achieve facial symmetry.
Encephalocraniocutaneous lipomatosis was first described by Haberland and Perou in 1970 (51). The infiltrative lipomatous lesions commonly affect the temporofrontal area unilaterally, cerebral tissues, and leptomeningeal tissues, as well as the skull, eye, and heart. Cutaneous lipomas are usually confined to the scalp, with involvement of the lower limb and back being more unusual. Additional abnormalities include marked mental retardation with associated cerebral malformations and calcification and early onset of seizures (51–54).
Shoulder girdle lipomatosis was initially described by Enzi et al (55) in 1992 in a report of six cases, all women between the ages of 38 and 72 years. These patients had gradually progressive unilateral enlargement of the shoulder and upper arm caused by lipomatous infiltration between the muscles of the extremity and thoracic wall (Fig 7). MR imaging and pathologic analysis revealed tissue identical to adult mature fat (56). Neuromyopathy, a clinical manifestation also found in multiple symmetric lipomatosis, was present in most patients (55), and compression of the upper airway may also occur.
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Figure 7a. Shoulder girdle lipomatosis in a 40-year-old man. (a) Clinical photograph shows diffuse infiltration and deformity of the shoulder and upper extremity. (b) CT scan reveals diffuse lipomatous infiltration largely affecting the subcutaneous tissues as the cause of the clinical disfigurement.
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Figure 7b. Shoulder girdle lipomatosis in a 40-year-old man. (a) Clinical photograph shows diffuse infiltration and deformity of the shoulder and upper extremity. (b) CT scan reveals diffuse lipomatous infiltration largely affecting the subcutaneous tissues as the cause of the clinical disfigurement.
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Adiposa dolorosa was originally described by Dercum in 1892 (57). This entity is characterized by multiple subcutaneous lipomas associated with pain and tenderness, features that are not associated with other forms of lipomatosis. Obese postmenopausal women (female-to-male ratio of 30:1) are almost invariably affected (57–59). Although the cause is unknown, an autosomal dominant inheritance with variable penetrance has been suggested. Adiposa dolorosa has also been associated with endocrine and lipid metabolism abnormalities. Patients also frequently have epilepsy and psychologic disease including emotional instability, depression, and dementia (57–59). The multiple lipomas associated with this disease commonly affect the pelvic girdle and thighs about the hips and knees (57–59). In addition to pain, patients also experience asthenia, motor weakness, and fatigability. Imaging and pathologic examination again demonstrate tissue identical to adult fat. Treatment of adipose dolorosa focuses on pain control and includes injection of lidocaine and steroids. Surgical resection and liposuction have also been employed in treatment, although these methods do not appear to halt disease progression.
Lipomatosis of Nerve
Lipomatosis of nerve was initially described in 1953 by Mason (60) and has been referred to in the past by various terms, including fibrolipomatous hamartoma of nerve, perineural lipoma, fatty infiltration of the nerve, intraneural lipoma, and neural fibrolipoma (60–66). In 2002, the WHO adopted the designation of lipomatosis of nerve (1). There is no known cause or hereditary predisposition for this lesion, although hypertrophy of mature fat and fibroblasts in the epineurium has been postulated.
Patients typically present before the age of 30 years and most commonly at birth or early childhood (60–66) (Figs 8, 9). The upper extremity is affected in 78%–96% of cases, particularly the median nerve (85% of cases) (60–66). The most frequent clinical manifestation is a slowly growing mass at the wrist, hand, or forearm. The ulnar nerve is the second most commonly affected site. The lower extremity is involved in 4%–22% of patients, with other reported cases affecting the radial nerve, brachial plexus, and cranial nerves (11). Pain and neurologic symptoms including carpal tunnel syndrome may be associated with lipomatosis of nerve. Macrodactyly is seen in 27%–67% of cases and has been referred to as macrodystrophia lipomatosa (11,64,66). We prefer to use the term lipomatosis of the nerve with or without macrodactyly. Additional causes of macrodactyly include angiomatosis, neurofibromatosis type 1, Klippel-Trénaunay-Weber syndrome, and Proteus syndrome (66). There is a male predilection in cases not associated with macrodactyly, whereas a female predominance has been noted in cases with digit overgrowth. The lesion also has a propensity to involve the second and third rays of the hand or foot.
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Figure 8a. Lipomatosis of the median nerve in a patient with macrodactyly. (a, b) Clinical photograph (a) and anteroposterior radiograph (b) show soft-tissue and bone overgrowth (arrow in b) of the second and third digits with osseous bowing. (c) Axial T1-weighted (500/20) MR image reveals diffuse overgrowth of fat in several digits (arrows). (d, e) Photographs of the sagittally sectioned gross specimen (d) and coronally sectioned whole-mount specimen (H-E stain) (e) of involved digits demonstrate osseous and soft-tissue hypertrophy with predominance of fat (*).
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Figure 8b. Lipomatosis of the median nerve in a patient with macrodactyly. (a, b) Clinical photograph (a) and anteroposterior radiograph (b) show soft-tissue and bone overgrowth (arrow in b) of the second and third digits with osseous bowing. (c) Axial T1-weighted (500/20) MR image reveals diffuse overgrowth of fat in several digits (arrows). (d, e) Photographs of the sagittally sectioned gross specimen (d) and coronally sectioned whole-mount specimen (H-E stain) (e) of involved digits demonstrate osseous and soft-tissue hypertrophy with predominance of fat (*).
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Figure 8c. Lipomatosis of the median nerve in a patient with macrodactyly. (a, b) Clinical photograph (a) and anteroposterior radiograph (b) show soft-tissue and bone overgrowth (arrow in b) of the second and third digits with osseous bowing. (c) Axial T1-weighted (500/20) MR image reveals diffuse overgrowth of fat in several digits (arrows). (d, e) Photographs of the sagittally sectioned gross specimen (d) and coronally sectioned whole-mount specimen (H-E stain) (e) of involved digits demonstrate osseous and soft-tissue hypertrophy with predominance of fat (*).
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Figure 8d. Lipomatosis of the median nerve in a patient with macrodactyly. (a, b) Clinical photograph (a) and anteroposterior radiograph (b) show soft-tissue and bone overgrowth (arrow in b) of the second and third digits with osseous bowing. (c) Axial T1-weighted (500/20) MR image reveals diffuse overgrowth of fat in several digits (arrows). (d, e) Photographs of the sagittally sectioned gross specimen (d) and coronally sectioned whole-mount specimen (H-E stain) (e) of involved digits demonstrate osseous and soft-tissue hypertrophy with predominance of fat (*).
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Figure 8e. Lipomatosis of the median nerve in a patient with macrodactyly. (a, b) Clinical photograph (a) and anteroposterior radiograph (b) show soft-tissue and bone overgrowth (arrow in b) of the second and third digits with osseous bowing. (c) Axial T1-weighted (500/20) MR image reveals diffuse overgrowth of fat in several digits (arrows). (d, e) Photographs of the sagittally sectioned gross specimen (d) and coronally sectioned whole-mount specimen (H-E stain) (e) of involved digits demonstrate osseous and soft-tissue hypertrophy with predominance of fat (*).
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Figure 9a. Lipomatosis of the median nerve in a patient without macrodactyly. (a) Axial T1-weighted (783/15) MR image of the wrist shows marked thickening of the median nerve with adipose tissue surrounding the nerve fascicles (arrowheads). (b) Longitudinal sonogram of the wrist also reveals cablelike thickening of the median nerve fascicles (arrowheads) with intervening hyperechoic fat. (c) Intraoperative photograph of the wrist dissection demonstrates a diffusely thickened, yellow median nerve (arrow) resulting from the lipomatosis of the nerve. (d) Photomicrograph (original magnification, x200; H-E stain) shows diffuse lipomatous infiltration (L) of the surrounding nerve fascicles (N).
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Figure 9b. Lipomatosis of the median nerve in a patient without macrodactyly. (a) Axial T1-weighted (783/15) MR image of the wrist shows marked thickening of the median nerve with adipose tissue surrounding the nerve fascicles (arrowheads). (b) Longitudinal sonogram of the wrist also reveals cablelike thickening of the median nerve fascicles (arrowheads) with intervening hyperechoic fat. (c) Intraoperative photograph of the wrist dissection demonstrates a diffusely thickened, yellow median nerve (arrow) resulting from the lipomatosis of the nerve. (d) Photomicrograph (original magnification, x200; H-E stain) shows diffuse lipomatous infiltration (L) of the surrounding nerve fascicles (N).
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Figure 9c. Lipomatosis of the median nerve in a patient without macrodactyly. (a) Axial T1-weighted (783/15) MR image of the wrist shows marked thickening of the median nerve with adipose tissue surrounding the nerve fascicles (arrowheads). (b) Longitudinal sonogram of the wrist also reveals cablelike thickening of the median nerve fascicles (arrowheads) with intervening hyperechoic fat. (c) Intraoperative photograph of the wrist dissection demonstrates a diffusely thickened, yellow median nerve (arrow) resulting from the lipomatosis of the nerve. (d) Photomicrograph (original magnification, x200; H-E stain) shows diffuse lipomatous infiltration (L) of the surrounding nerve fascicles (N).
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Figure 9d. Lipomatosis of the median nerve in a patient without macrodactyly. (a) Axial T1-weighted (783/15) MR image of the wrist shows marked thickening of the median nerve with adipose tissue surrounding the nerve fascicles (arrowheads). (b) Longitudinal sonogram of the wrist also reveals cablelike thickening of the median nerve fascicles (arrowheads) with intervening hyperechoic fat. (c) Intraoperative photograph of the wrist dissection demonstrates a diffusely thickened, yellow median nerve (arrow) resulting from the lipomatosis of the nerve. (d) Photomicrograph (original magnification, x200; H-E stain) shows diffuse lipomatous infiltration (L) of the surrounding nerve fascicles (N).
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At gross pathologic examination, the affected nerve is diffusely enlarged by yellow fibrofatty tissue. Histologic evaluation reveals that the fatty infiltration separates individual nerve bundles (1). This infiltrative pattern allows distinction from a soft-tissue lipoma that lies adjacent to nerve. The nerve fibers are usually intrinsically normal, although atrophy has been reported late in the disease. The pathologic appearance is the same, regardless of the presence or absence of macrodactyly. Macrodactyly results in disproportionate fibroadipose tissue overgrowth in the affected digits.
Radiographs of patients without associated macrodactyly often appear normal, although a soft-tissue mass may be seen. Macrodactyly causes soft-tissue and osseous overgrowth, both longitudinally and axially (66) (Figs 8, 9). Bone overgrowth is typically more prominent volarly and distally, often resulting in osseous bowing. The osseous overgrowth usually does not progress after puberty. The bone deformity may lead to premature osteoarthritis. Soft-tissue overgrowth often appears as increased radiolucent tissue that corresponds to fat.
The imaging appearance, particularly with sonography and MR imaging, of advanced lipomatosis of nerve is usually pathognomonic and reflects the underlying disease (62,63,65,66) (Figs 8, 9). Sonography reveals alternating hyperechoic (fat) and hypoechoic (nerve fascicles) bands in a diffusely enlarged nerve, thus creating a cablelike appearance. The MR imaging appearance is similar, with longitudinally oriented cylindrical areas of low to intermediate signal intensity (nerve fascicles) surrounded by adipose tissue in a diffusely thickened nerve. Increased fat content in the digits is also apparent in patients with macrodactyly on MR images (Fig 8).
There is no effective treatment for lipomatosis of nerve, as complete resection is usually contraindicated owing to the severe sensory and motor deficits that result. Carpal tunnel release may relieve some symptoms because of decompression in patients with median nerve involvement. Macrodactyly may be treated with amputation because of the extensive associated deformity.
Lipoblastoma and Lipoblastomatosis
Lipoblastoma is a rare benign mesenchymal tumor of embryonal white fat that occurs in infancy and early childhood. In 1926, Jaffe (67) used the term lipoblastoma to describe an atypical lipomatous tumor of the groin. In 1958, Vellios and co-workers coined the term lipoblastomatosis to describe an infiltrating lesion of the anterior chest wall (68). Chung and Enzinger (69) suggested using "benign lipoblastoma" for the circumscribed lesion, and "benign lipoblastomatosis" for the diffuse, infiltrating lesion. The circumscribed lipoblastoma is more common (approximately 70% of cases) and is located in the superficial soft tissues. The diffuse type lipoblastomatosis (about 30% of cases) has an infiltrative growth pattern that affects the subcutaneous tissue and underlying muscle.
In 1973, Chung and Enzinger (69) published the largest series to date, in which 88% of patients were less than 3 years of age, median age of onset was 1 year old, and the oldest patient was 7 years old. Lipoblastomas discovered after the age of 10 years are rare. Lesions have been reported to occur approximately two to three times more frequently in males (69).
Lipoblastomas most commonly manifest as asymptomatic, painless, progressively growing masses in the superficial or subcutaneous soft tissue of the extremities (19,70–81). Less common locations include the trunk, neck, retroperitoneum, mediastinum, and perineum (Fig 10). Symptoms associated with these lesions are directly related to the location and size of the mass. Upper respiratory symptoms, fever, and intermittent airway obstruction have been described in patients with pleural-based, mediastinal, pulmonary, and lower neck lipoblastomas (101–120). Emesis, diarrhea, anorexia, and abdominal pain have been described in patients with mesenteric or retroperitoneal lipoblastomas (79).
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Figure 10a. Lipoblastoma in a 4-month-old boy with an anterior neck mass. (a) Axial contrast-enhanced CT scan shows a mass extending from the left side of the neck and deviating the trachea to the right. The periphery of the mass is composed of small foci of fat (arrowhead) separated by thin septa and areas of low attenuation representing myxoid tissue (curved arrow). A larger focus of soft-tissue attenuation (straight arrow) is present centrally. (b) Photograph of the axially sectioned gross specimen shows a solid central element (arrow). Note lack of the typical yellow color of fat in the surrounding lobules (*) secondary to an admixture of adipose and myxoid tissue in this lipoblastoma.
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Figure 10b. Lipoblastoma in a 4-month-old boy with an anterior neck mass. (a) Axial contrast-enhanced CT scan shows a mass extending from the left side of the neck and deviating the trachea to the right. The periphery of the mass is composed of small foci of fat (arrowhead) separated by thin septa and areas of low attenuation representing myxoid tissue (curved arrow). A larger focus of soft-tissue attenuation (straight arrow) is present centrally. (b) Photograph of the axially sectioned gross specimen shows a solid central element (arrow). Note lack of the typical yellow color of fat in the surrounding lobules (*) secondary to an admixture of adipose and myxoid tissue in this lipoblastoma.
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The natural history of lipoblastomas is to evolve into mature lipomas. In 1947, Van Meurs (82) described this maturation process in a 5-year-old girl who underwent five resections of an axillary lesion over 20 months. Ha and colleagues (19) described a similar progression over a 5-year period in another patient. Complete spontaneous resolution of a case of lipoblastomatosis has also been reported in a 2-day-old patient with a congenital thigh mass who was followed up for 1 year (74).
At gross pathologic examination, the tumors are light yellow, yellowish gray, white, tan, pink, or red. These tumors are frequently less than 5 cm, but larger lesions, including a 17-cm omental lipoblastoma, have been reported (1,4,83). The circumscribed lipoblastoma is partially or fully encapsulated, whereas lipoblastomatosis is infiltrative and lacks a capsule. At histologic analysis, these lesions are composed of monovacuolated and multivacuolated lipoblasts, spindled to stellate mesenchymal cells, a plexiform capillary network, myxoid stroma, and mature adipocytes organized into lobules separated by fibrous septa. In our experience, the myxoid component is often most prominent in very young patients. A "signet-ring" appearance is seen when lipoblasts are relatively small and round with a single vacuole-like fat droplet. If the lipoblasts have finely vacuolated eosinophilic cytoplasm, they may closely resemble hibernoma cells. Ultrastructural observations (ie, with electron microscopy) suggest that lipoblastomas contain a spectrum of differentiating cells ranging from prelipoblasts (spindle cells) to mature adipocytes. Diffuse lipoblastomas have a less pronounced lobular pattern and can contain skeletal muscle fibers related to the infiltrative growth pattern. Lipoblastomas have chromosomal aberrations with pseudodiploid karyotypes. The characteristic cytogenetic abnormalities are deletions and rearrangement of 8q11–13 seen in the vast majority of patients (81). Lipoblastomas lack the t (12,16) translocation seen in myxoid liposarcomas (1,83).
The imaging appearance of lipoblastoma and lipoblastomatosis reflects the underlying pathologic characteristics and varies depending on the extent of fat versus myxoid stroma. Radiographs may reveal a soft-tissue mass with radiolucency. Lipoblastoma is well defined, often with a lobular appearance and internal septations, at sonography, CT, and MR imaging. Sonography, CT, and MR imaging demonstrate fat in lipoblastoma as echogenic regions, areas of low attenuation, or areas of signal intensity identical to that of subcutaneous adipose tissue with all pulse sequences, respectively (11,12,19). In many patients, particularly older children, fat is the predominant feature of these lesions, and they appear identical to a lipoma, with the diagnosis suggested because of the patients’ young age (11,12,19) (Fig 10). However, in very young patients (infants), the myxoid components may predominate with only small elements of fat (11,12,19). These myxoid areas are hypoechoic at sonography, low attenuation at CT, and at MR imaging are low signal intensity with T1-weighted sequences and high signal intensity with T2-weighted sequences, reflecting their high water content (Fig 10). These areas also enhance with contrast material, owing to the rich capillary network. Lipoblastomas with this imaging appearance are indistinguishable from a myxoid liposarcoma. However, the age of the patient is vital in allowing accurate diagnosis. Liposarcomas are extraordinarily rare in patients less than 10 years of age (two cases of 2500 in the Armed Forces Institute of Pathology series, both presenting after the age of 2 years) (84–86). Thus, a lesion containing fat in a young child (less than 2 years old), even with prominent or predominant nonlipomatous components, is almost invariably a lipoblastoma. Lipoblastomatosis reveals similar intrinsic imaging features but also demonstrates infiltrative growth involving both subcutaneous tissue and muscle without a surrounding capsule.
The treatment of lipoblastoma and lipoblastomatosis is wide surgical resection. Recurrence develops in 9%–25% of cases and is largely associated with the infiltrative lipoblastomatosis owing to incomplete resection (68,69,72). These lesions have no metastatic potential.
Angiolipoma
Angiolipoma was originally described by Howard and Helwig in 1960 (87). It represents a benign subcutaneous lesion most commonly affecting young male patients in the 2nd to 3rd decades of life. The most frequent site of involvement is the forearm followed by the trunk and upper arm. Multiple lesions are seen in approximately 70% of cases (83,88–93). The genetic pattern is unclear, although some cases demonstrate autosomal dominant inheritance. The familial prevalence is estimated at 5% (6,88).
Angiolipomas manifest as small (< 2 cm), slowly growing, subcutaneous mass or masses that are painful to palpation. The pain often diminishes over time and is not intensified by thermal changes. Trauma has been invoked as a possible contributing cause.
At gross examination, these lesions are always encapsulated, subcutaneous yellow nodules with reddish areas corresponding to vessels. The vessels are small caliber capillaries and often contain fibrin thrombi with surrounding mature fat (Fig 11). Lesions previously described as being deep infiltrating angiolipomas have now been recognized by the WHO as being intramuscular hemangiomas, a nomenclature we have employed for many years (1,94). In our opinion, subcutaneous lesions may also represent ablated capillary hemangiomas.
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Figure 11a. Angiolipoma in the subcutaneous thigh of a 21-year-old man. (a, b) Coronal T1-weighted (500/14) (a) and axial proton-density fat-suppressed (2000/30) (b) MR images show a subcutaneous mass that is largely isointense relative to fat (arrows). Several small nodular foci are also seen that have a more serpentine appearance (arrowheads), suggestive of vessels on the fat-suppressed MR image (b). (c) Photomicrograph (original magnification, x150; H-E stain) reveals a lipomatous mass (L) with more cellular areas peripherally (arrows). The more cellular peripheral area, shown in a higher power insert (original magnification, x400; H-E stain), contains multiple fibrin microthrombi in small-caliber vessels (arrowheads).
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Figure 11b. Angiolipoma in the subcutaneous thigh of a 21-year-old man. (a, b) Coronal T1-weighted (500/14) (a) and axial proton-density fat-suppressed (2000/30) (b) MR images show a subcutaneous mass that is largely isointense relative to fat (arrows). Several small nodul | |
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Abstract
LEARNING OBJECTIVES FOR TEST...
