[Occult acoustic neurinoma].

A case of small occult schwannoma in a 73-year-old man is reported. Histopathological sections of the temporal bone revealed a tumor in the left internal auditory meatus. The tumor measured about 5 x 6 mm in size. There were whorls of spindle shaped cells with the typical palisading characteristic of acoustic neurinoma-Antoni A type. The posterior wall of the meatus had been eroded but the nerve fibers were intact. It seems to have raised from the cochlear nerve trunk and was displaced and compressed. Slight degeneration of the spiral ganglion cells and the cochlear nerve fibers was found. There was a very fine granular eosinophilic precipitate throughout the perilymphatic space. This probably represents increased protein content in the perilymph. Thickening of the walls of the internal auditory artery and some vessels of striae vasculares was also noted. The organs of Corti, the maculae of the utricle and saccule and the cristae of semicircular canals appeared normal.