Chondroid lipomas are rare benign soft tissue tumors that contain a varied ratio of both fat and cartilage. These lesions can be diagnostically confusing as they may mimic other fat-containing neoplasms, including more aggressive lesions such as myxoid liposarcoma and extraskeletal myxoid chondrosarcoma 1.
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Epidemiology
These tumors are rare with the age at presentation ranging from 14-70 years of age, with a strong female predilection (F:M 4:1).
Clinical presentation
Chondroid lipomas present as painless masses, sometimes with groth. They most commonly arise an appendicular distribution, with lesions most frequently encountered in the proximal extremities and limb girdles 6,10. There are, however, cases reported in many other locations including the trunk, head and neck and even the oral cavity 6,7,10.
Pathology
Histologic features that suggest chondroid lipoma include a fibrous capsule with nests and cords of uni and multivacuolated round mature adipocytes within an extracellular myxohyaline matrix that has a cartilaginous appearance. The proportion of myxoid-chondroid matrix and adipose tissue is variable. These lesions may have rich vascularization 2,10.
Immunohistochemistry
To arrive at a specific diagnosis of chondroid lipoma, immunohistochemical analysis may assist in distinguishing these lesions and myxoid liposarcoma or other more aggressive tumors 2.
S100: positive particularly in the mature adipocytes
EMA: negative
Genetics
Chondroid lipomas are associated with fusion of the C11orf95 and MRTFB genes resulting from a recurrent (11;16)(q13;p13) chromosomal translocation 10.
Radiographic features
These lesions may vary from predominately fat 4 to predominately chondroid tissue 3,6, with imaging features that match the relative distribution of constituent tissues. They also range from sub-centimeter to rather enormous. It is worth keeping in mind that imaging characteristics have not been extremely well-documented due to the rarity of this lesion and recent first description, in 1993.
Plain radiograph and CT
Often seen as a mass like lesion of low density tissue (typically of fat attenuation) with or without internal calcification of the cartilaginous regions; however, fat may not be a prominent feature and may not be readily identifiable 3-5.
MRI
Described features include a lobulated, encapsulated mass with areas that show typical fatty signal to a variable degree, with high signal on T1 and T2WI, suppressing with fat saturation. Cartilaginous portions of the lesion will show inhomogeneously increased signal on fluid sensitive fat-suppressed images. Areas of calcification within the mass will appear hypointense on all pulse sequences 3-5,9.
Contrast enhancement
Lesions may show heterogeneous and/or peripheral enhancement 9.
PET
Lesions may be prominently 18F-FDG avid 8.
Treatment and prognosis
Chondroid lipomas are being circumscribed masses and surgical excision is therefore usually curative 10. Malignant transformation and metastases are not reported.
Differential diagnosis
Imaging differential considerations include: