PERINEURIOMA WITH OSSIFICATION - A CASE-REPORT WITH IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL STUDIES

We present the case of a peripheral nerve sheath tumor arising from th e sciatic nerve in the thigh of a 42-year-old woman. Histologically, t he tumor was composed of fascicles of spindle cells with extremely att enuated cytoplasmic processes. Regions of the tumor were heavily miner alized and fibrotic. The tumor was epithelial membrane antigen-positiv e and S100-negative. Staining for Leu-7 was positive in a patchy distr ibution. Type IV collagen was present between cells, and CD34 was nega tive in the tumor cells. Ultrastructural features included elongate ce llular processes surrounded by discontinuous basal lamina and collagen . The features of the tumor therefore meet criteria for perineurioma. This rare tumor is found most often in the extremities in middle-aged woman. To our knowledge, the presence of bone formation in a perineuri oma has not been described previously. The differential diagnosis incl udes other peripheral nerve sheath tumors, low-grade fibrous tumors, a nd synovial (monophasic) tumors. Evidence provided by electron microsc opy and immunohistochemistry supports the diagnosis and classification of this unusual nerve sheath tumor as perineurioma with ossification. These findings expand our knowledge and criteria for classifying peri pheral nerve sheath tumors.