COCHLEAR MICROPHONIC POTENTIALS IN PATIENTS WITH VESTIBULAR SCHWANNOMAS

We evaluated the cochlear function of 44 patients with unilateral vest ibular schwannomas by measuring cochlear microphonic potentials (CM) i n electrocochleography. We used short tone bursts with 0.5-, 1-, 2-, a nd 4-kHz frequencies as acoustic stimuli to evoke CMs, and determined CM detection thresholds. The CM detection thresholds in vestibular sch wannomas ranged from normal to no response. Cochlear dysfunction was s een in 35 (79.5 %) of the 44 cases; these patients had higher CM detec tion thresholds than normal subjects. Although a significant correlati on was found between mean hearing level (0.5-4 kHz) and mean CM detect ion threshold (0.5-4 kHz), 20 patients had lower CM detection threshol ds than were found using audiometry. This suggests that there is an ad ditional retrocochlear component responsible for this hearing loss.