High-grade epithelioid angiosarcoma of the scalp. An immunohistochemical and ultrastructural study.

The ultrastructural and immunohistochemical characteristics of a high-grade epithelioid angiosarcoma of the scalp are reported. By light microscopy, the neoplasm simulated a poorly differentiated carcinoma, either primary or metastatic from some occult site. Immunohistochemical study, using a specific antibody against factor VIII-related antigen, was positive when direct immunofluorescence was applied to frozen specimens of the neoplasm. Application of immunoperoxidase (avidin-biotin complex method) on paraffin-embedded tissue using the same antibody was negative. Ultrastructually, the neoplasm had a prominent cytoskeleton of intermediate filaments, numerous pinocytotic vesicles, small intercellular lumina with microvilli on their surfaces, and characteristic intracytoplasmic vacuoles. A brief discussion of the differential diagnostic features is made.