Audiometric abnormalities in hemifacial spasm.

Abstract

One-hundred forty-three patients with hemifacial spasm (HFS) as a primary disorder were evaluated pre- and postoperatively by pure-tone and speech audiometry, determination of thresholds for the acoustic middle ear reflex, and recording of auditory brainstem responses. We found an unusual 'notch' in the pure-tone audiograms of 16 patients (11%) and a low-frequency up-sloping pure-tone threshold in another 17 patients (12%). Because such abnormalities occur rarely, it may be assumed that they are related to these patients' primary disorder. All of the patients underwent microvascular decompression to relieve their spasms, and it was confirmed during surgery that in all patients the seventh cranial nerve was compressed at its root entry zone by vascular structures. It is therefore assumed that the abnormality of pure-tone threshold function noted in 23% of the patients with HFS was caused by compression of the auditory nerve by the same vessel as that which compressed the facial nerve. Since the changes in the pure-tone threshold occurred in the mid- and low-frequency range, it is assumed that low-frequency fibers constitute the outer part of the auditory nerve at its entrance into the human brainstem.