Asymptomatic schwannoma of the cochlear nerve.

During systematic study of temporal bone histopathology at The Deafness Foundation, Memphis, we found an unsuspected small schwannoma arising solely from the cochlear nerve, compressing the facial nerve within the internal auditory canal. The primary temporal bone pathologic finding was bilateral otosclerosis. Compression of the facial nerve by schwannomas of the cochlear nerve is well know to occur at a late stage and produce a lower motor neuron facial paralysis but, in the present case, although the growth of th tumor compressed the facial nerve trunk, no paralysis was noted. Hearing test of the ear associated with the tumor, performed ten months before death, revealed a mixed conductive-sensorineural deafness. Surprisingly, the speech reception threshold was 75 dB, with a speech discrimination score of 70%.