Localization: (a) Superficial (frequent): in the subcutaneous tissue of the back, shoulder, neck, and proximal extremities. (b) Deep (rare): within or between muscles or adherent to bone, tendons, joints or nerves. In 5 % of cases lipomas are multiple with symmetrical distribution in the dorsum and proximal upper limb.
Clinical: Solitary lump, slow growing, and painless unless there is nerve compression. Superficial lipoma never grows large size (average 4 cm.) and it is movable. Deep lipoma tends to be larger (average 10 cm) and with a spherical, fixed, and firm mass.
Imaging: On X-ray, a radiolucent mass with or without calcification or ossification; mild cortical thickening when parosteal. On CT scan, a lobulated, sharply marginated radiolucency with homogeneous density. On MRI, an encapsulated, bright mass without enhancement after contrast administration; signal intensity equal to that of fat; regular thin septation. On angiography, avascular. On bone scan, there is no uptake.
Histopathology: It is often lobulated with a very thin true capsule and pseudocapsule fibrous, thick, and adherent to the surrounding tissues. Soft on palpation, pale yellow in color, lipoma is constituted by lipocytes, mature “signet ring” cells. Vessels are not very apparent, because they are thin and compressed by lipocytes. On immunohistochemistry, all lipomas are diffusely positive for S-100 and vimentin. Spindle cell and pleomorphic lipoma are also positive for CD34.
Course and Staging: a) Superficial lipoma: easily diagnosed, asymptomatic, generally stage 1, but it may behave as active stage 2 lesion. According to AJC classification, lipoma is more frequently stage Ia. b) Deep lipoma: an extensive anatomo-pathological study with multiple specimens is necessary to exclude liposarcoma lipoma-like. Usually, stage 2 or stage Ib according to AJC classification. Malignant changes are exceptional.
Treatment: Marginal excision is curative. Recurrence is rare (<5 %).
Network of capillaries with fibrin thrombi
Spindle cell lipoma
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