ABSTRACT
A 45-year-old Indian man had a painful, slow growing swelling on the anterior aspect of the right thigh, clinically assumed to be a sebaceous cyst, associated with varicose veins and venous oedema of the right leg. The excised mass [25x23x15 mm] consisted of a large blood-filled space [20mm] devoid of endothelial cells surrounded by a wall [2 to 6 mm] with features of a fibrous histiocytoma. Tumor cells were positive for vimentin, macrophages were positive for MAC375 and focally for S100. Scattered T-lymphocytes present were CD3 positive, CD20 negative. The cyst lining was negative for factor VIIIRAg and CD34, Staining for actin, desmin, cytokeratin, Ki67 and PCNA was negative. Aneurysmal fibrous histiocytoma is a rare variant of cutaneous fibrous histiocytoma characterized by large blood-filled spaces devoid of endothelial cells. Because of the large size and rapid growth secondary to hemorrhage it may be clinically confused with cysts, benign and malignant tumors