BIPOLAR COCHLEAR NERVE RECORDING TECHNIQUE - A PRELIMINARY-REPORT

To preserve hearing during vestibular neurectomy and acoustic neuroma removal, the cochlear nerve must be identified. Present techniques, in cluding monitoring eighth nerve action potentials, help the surgeon id entify those maneuvers that increase the risk of nerve injury but do n ot help in the anatomic identification of the cochlear nerve or the co chlear-vestibular cleavage plane. The purpose of this study was to dem onstrate an electrophysiologic method of identifying the cochlear port ion of the eighth cranial nerve. A flush-tipped, bipolar electrode rec ording probe was used to directly record responses to monaural click s timuli from the cochlear nerve but not from surrounding tissue. It was also used to delineate the cochlear-vestibular cleavage plane. Stimul us intensity levels over 25 dB sensation level tended to reduce the ac curacy of nerve identification, and lower levels prolonged recording t ime. This technique and its application to posterior fossa surgery is discussed.