PLEOMORPHIC LIPOMA
Bizarre multinucleated cells in a background of mature adipose tissue and loosely textured collagen in a subcutaneous tumor are characteristic of pleomorphic lipomas. These are usually located in the same regions as spindle cell lipomas (back of neck or shoulders), and one occasionally finds tumors having mixed features of pleomorphic lipoma and spindle cell lipoma. These are found more commonly in males. Cells resembling lipoblasts may be present, and mitotic figures can be seen, but these tumors are benign. The nuclear chromatin has a peculiar smudged appearance, and there may be vacuoles within the nuclei. 'Floret cells' are often present, but these are not specific. Scattered large collagen bundles form part of the loose collagenous stroma. Some people include this tumor with 'atypical lipomas', but other people use the term 'atypical lipoma' to include well differentiated liposarcomas of the subcutis. Fortunately, liposarcomas restricted to the subcutis are extremely rare.

 
Gross appearance.
Low power showing scattered, bizarre, multinucleated cells in a background of mature adipose tissue and loosely textured collagen. Some of the collagen bundles are large.
Medium power view showing bizarre cells.
 High power view showing a cell resembling a lipoblast. Note the peculiar smudged appearance of the very dense nuclear chromatin.
High power view of a floret cell. The ring of nuclei is characteristic.
High power view of bizarre cells.

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