PERINEURIOMA - AN UNUSUAL CAUSE OF AN EXTERNAL AUDITORY-CANAL POLYP

A 33-year-old woman presented with pruritus of the right ear and on ex amination was found to have 1 x 1 cm polypoid lesion in the external a uditory canal. This was removed and histological examination revealed a well-circumscribed spindle cell lesion arranged in fascicles and who rls. Immunohistochemistry showed the tumor to be EMA-positive but S-10 0-, desmin-, actin-, and cytokeratin-negative. Ultrastructural examina tion confirmed perineurial cell origin. There are several lesions in w hich perineurial cells are present, but a true perineurioma is compose d exclusively of perineurial cells. It has characteristic morphologica l, immunohistochemical and ultrastructural features that help separate it from other nerve and neuroectodermal lesions.