Lipomas are the most common soft tissue tumors being present in an estimated 1-2% of the population. They are benign, typically painless, and are most often located in the subcutaneous soft tissues of the proximal extremities, back, neck, and buttocks. Most lipomas develop in adulthood, without significant variation in gender or ethnicity. Lipomas are composed of encapsulated mature adipocytes (fat cells) that appear yellow and homogenous grossly. Lipomas maintain a relatively stable size once developed, independent of metabolic changes that may occur to the surrounding subcutaneous fat.
The initial presentation of a lipoma is usually that of a soft, painless, and freely mobile subcutaneous tumor without appreciable connection to the skin above. Trauma to the tumor may produce fat necrosis and/or dystrophic calcification, making it firmer to palpation. Rarely, the lipoma may produce a mass effect on nearby neurovascular structures, causing pain with deep palpation or compression. Imaging may be performed to rule out more atypical soft tissue tumors, but a classical clinical presentation is usually sufficient to establish the diagnosis. Surgical excision is curative, with spontaneous recurrences rare in the literature. Tissue should always be submitted for pathological examination to confirm benignancy.
Less common variants of lipomas include benign tumors such as angiolipomas, chondroid lipomas, fibrolipomas, and myxolipomas. Hibernomas are similar to lipomas, but are composed of brown, immature adipocytes. Liposarcomas are malignant fatty tumors usually found deep to the muscular fascia. There are several rare syndromes associated with genetic predisposition to lipomas including Cowden syndrome, Bannayan-Riley-Ruvalcaba, Multiple Endocrine Neoplasia type 1, and Proteus syndrome.
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