Nerve sheath tumors of the paranasal sinuses: electron microscopy and histopathologic diagnosis.

Tumors of the nerve sheaths are very unusual. They occur with the highest frequency in the head and neck region, yet only 4% have been found to occur within the paranasal sinuses. Only 40 cases of nerve sheath tumors with direct involvement of the paranasal sinuses have been reported in the world's literature to date. Three new cases of neurofibroma not associated with Recklinghausen's disease and one case of a schwannoma of the frontoethmoid and maxillary sinuses are presented. The clinical, radiographic, and histopathologic features of these lesions will be discussed with emphasis on electron microscopy and immunohistochemical differentiation of these rare and often confusing lesions.