Intraoperative measurements of auditory-evoked potentials in three patients with acoustic neuroma.

Auditory brainstem responses (ABRs), electrocochleograms and the evoked potentials from the internal auditory canal were recorded simultaneously in 3 acoustic neuroma (AN) patients. The neural conduction in the internal auditory canal was examined by recording the compound action potentials of the cochlear nerve. In an AN patient with wave I only in the ABR, the neural conduction of the excitement in the cochlear nerve was blocked within the internal auditory canal. In 2 AN patients with elongated interpeak latency differences between waves I and V in ABRs, the neural conduction velocity of the cochlear nerve was lower than that of normal subjects. These results provide neurophysiological evidence that low neural conduction velocity in the cochlear nerve results in the abnormal ABR.