Auditory pathway function after vestibular schwannoma surgery.

We studied seven patients before and after vestibular schwannoma surgery. Four patients became unilaterally profoundly deaf and three patients preserved their hearing. Cortical responses were recorded with a 122-channel whole-scalp SQUID neuromagnetometer using tone-burst stimuli to the healthy ear. Brainstem auditory evoked potentials (BAEPs) were measured using alternating clicks. Ten healthy volunteers served as a control group. In patients, preoperative cortical response latencies and strengths did not differ significantly from those of controls. However, 6 months after the operation the latency was, on average, 7 ms longer than preoperatively over both hemispheres. BAEPs were in the normal range both before and after the operation. These results suggest that unilateral lesion in peripheral auditory pathways also affects cortical reactivity to stimuli presented to the non-affected ear, possibly reflecting altered binaural interaction in the auditory pathways.