Fine needle aspiration cytology of perineurioma. Report of a case with histologic, immunohistochemical and ultrastructural studies.

The fine needle aspiration (FNA) findings are presented for a case of perineurioma, a benign soft tissue tumor composed of perineurial cells, which are epithelial-like and ensheath the endoneurial connective tissue space of nerve fibers. A subcutaneous FNA performed on a posterior thigh mass of a 14-month-old boy produced a specimen consisting of numerous spindle-shaped tumor cells with bipolar cytoplasmic extensions and occasional pseudosignet-ring cells in a prominent myxoid background. Cytologically, a diagnosis of benign myxoid tumor was made. Histologic examination of the resected tumor revealed the characteristic features that have been described for perineurioma; the diagnosis was confirmed with immunocytochemical and ultrastructural studies. Perneurioma should be included in the differential diagnosis of benign myxoid neoplasms seen in FNA biopsy specimens.