LIPOMATOUS HEMANGIOPERICYTOMA - A HISTOLOGIC, ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL STUDY OF A UNIQUE VARIANT OF HEMANGIOPERICYTOMA

We report three cases of a unique, previously undescribed soft tissue tumor composed of mature adipocytes and hemangiopericytomatous areas, for which we propose the term lipomatous hemangiopericytoma. The tumor s occurred in adults and were located in the sinonasal area, the soft tissue of the shoulder, and the retroperitoneum. The tumors ranged in size from 4 to 10 cm in greatest diameter and grossly were solid and r anged from tan to yellow. Histologically, they were composed of a vari able admixture of benign lipomatous and hemangiopericytomatous compone nts. Immunohistochemically, they stained with antibodies to vimentin a nd not to alpha-smooth-muscle actin, muscle-specific actin, desmin, S- 100 protein, glial fibrillary acidic protein, epithelial membrane anti gen, or keratin. Ultrastructurally, the cells constituting the hemangi opericytomatous areas had the features of pericytes, and no lipoblasts or transitional forms between lipocytes and pericytes were found. The histologic differential diagnosis of this neoplasm includes spindle-c ell lipoma, angiolipoma, liposarcomas, tumors showing smooth muscle an d adipocytic differentiation, and hemangiopericytoma infiltrating fat. Because of the small number of cases and the limited follow-up, we ca nnot be certain of their biologic behavior, although we expect that th ey are benign. Lipomatous hemangiopericytoma represents a distinctive pathologic entity that should be recognized and studied further.