Perineural cell tumor. Immunocytochemical and ultrastructural characterization. Relationship to other peripheral nerve tumors with a review of the literature.

A perineurial cell tumor occurred in the shoulder girdle of a 47 year old woman. Light microscopy demonstrated a well-differentiated spindle-cell neoplasm of uncertain histogenesis. Immunocytochemical staining for S-100 protein was negative. Ultrastructural study revealed tumor cells with characteristics of perineurium, e.g. large numbers of micropinocytotic vesicles, numerous intercellular junctions, and elongated cell processes surrounded by basal lamina. Tumors of perineurial cells should be distinguished from the commonly recognized schwannomas as well as from various soft tissue lesions so that their biologic behavior can be better defined. A review of three other reported cases of perineurial cell tumors suggested that these tumors are benign and are usually located in the extremities and shoulder girdle. In addition, perineurial cell proliferation has been identified in other lesions of peripheral nerves, such as neurofibromas and localized hypertrophic neuropathy. Immunocytochemical and ultrastructural study of spindle-cell lesions with unusual histologic features may reveal that perineurial cell proliferation occurs more frequently than currently recognized.