MENINGIOMA-LIKE TUMOR OF THE SKIN - AN ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL STUDY

Three unusual cutaneous tumors are described along with ultrastructura l and immunohistochemical studies. All lesions were asymptomatic red-b rown papulonodules. Light microscopic examination revealed a whorled c onfiguration of spindle-shaped cells, some concentrically arranged aro und blood vessels. Immunohistochemical panels exhibited positive stain ing only with antibody to vimentin and negative staining with antibodi es against S-100 protein, muscle markers, cytokeratin, epithelial memb rane antigen, Leu 7, type IV collagen, and factor XIIIa, ruling out ob vious nevomelanocytic, nerve sheath, meningothelial, smooth muscle, an d perithelial differentiation. Electron microscopic examination demons trated cells producing poorly formed collagen fibrils, sparse collagen fibers, and possessing occasional ill-defined intercellular junctions between their elongated cell processes. This rare tumor is considered to be either an immature fibrohistiocytic or possibly a nerve sheath neoplasm with striking similarities to so-called canine hemangiopericy toma. Because the prominent whorled pattern was reminiscent of meningi oma, the lesion was referred to as meningioma-like tumor of the skin.