Cutaneous lipomatous neoplasms.

Benign and malignant lipomatous tumors are the most common neoplasms of subcutaneous and deep soft tissues in adults. In contrast, purely cutaneous lipogenic neoplasms are exceptionally rare, and some entities and variants of adipocytic neoplasms have not yet been described in the skin. In addition, some dermal lipogenic neoplasms are characterized by different specific clinicopathologic features in comparison with more deeply located tumors. Cutaneous angiolipoleiomyoma ("angiomyolipoma") is seen most often in male patients and in an acral location. It is characterized histologically by mature adipocytes, thick-walled blood vessels, and smooth muscle cells arranged in well-defined fascicles and around blood vessels. Smooth muscle cells in cutaneous angiolipoleiomyoma stain negatively for HMB-45, in contrast to renal and extrarenal angiomyolipoma. Adenolipoma of the skin is a superficially located form of lipoma composed of large lobules of mature adipocytic tissue admixed with eccrine ducts and glands. Cutaneous spindle cell/pleomorphic lipomas, in contrast to subcutaneous forms, are more common in female patients and have a wide anatomic distribution. Histologically, cutaneous spindle cell/pleomorphic lipomas are characterized by an infiltrative growth pattern mimicking more aggressive lesions. Rarely, liposarcoma may occur as a purely cutaneous lesion with a favorable clinical prognosis despite high-grade morphologic features in many cases.