Image Description
Microscopic Features: The spindle cells are arranged in short, irregular fascicles in a fibromyxoid matrix often containing thick collagen bundles. There may be prominent nuclear palisading, similar to that seen in schwannomas. Some tumors are sparsely cellular and contain abundant myxoid matrix, mimicking a myxoma. The background matrix contains numerous mast cells. Foci of osseous or cartilaginous metaplasia may be present.
About the Disease
Spindle cell and pleomorphic lipomas are uncommon benign lipomatous tumors with overlapping clinical, morphologic, and cytogenetic features. They represent morphologic continuum of the same entity. They occur in 45-60 yr. age group with a strong male predilection. Majority (80%) arise in the posterior neck, shoulder, or upper back as slow-growing, solitary, well-circumscribed, firm, painless subcutaneous nodules, usually < 5 cm in size.The morphology depends upon the relative proportion of mature adipose tissue, spindle cells, and fibromyxoid stroma. Some tumors are lipoma-like with abundant fat and only scattered foci of spindle cells. Others are grey-white firm tumors composed of spindle/pleomorphic cells with only rare foci of adipose tissue. The background stroma is fibromyxoid or collagenous with abundant mast cells and thick ropy collagen bundles. Pleomorphic lipomas resemble spindle cell lipomas but also contain floret giant cells with hyperchromatic nuclei in a wreath-like arrangement.Deletions of 13q14 (or entire chromosome 13) with loss of tumor suppressor gene RB1 are found in the majority of cases. The same deletion is also found in cellular angiofibroma and mammary and soft tissue myofibroblastomas.