Intraoperative electrically evoked vestibular potentials in humans.

Electrically evoked short latency vestibular potentials were recorded in 9 patients during vestibular neurectomy. Patients were operated on because of intractable Meniere's disease. The VIIIth cranial nerve was exposed through a limited retrosigmoidal approach; the vestibular nerve was contacted in the cerebello-pontine angle with a bipolar platinum-iridium electrode and stimulated with biphasic current pulses (100 microseconds/phase, 0.75-1 mA p-p, 20/s). The responses were recorded over 12.8 ms between a forehead and an ipsilateral ear lobe electrode. Each recording consisted of 2 x 1,000 averaged responses. A systematically reproducible vertex-negative potential occurring at a latency of approximately 2 ms and having an amplitude of approximately 0.5 microV was recorded in all patients. This vertex-negative potential disappeared after selective vestibular neurectomy proximal to the stimulation site. Simultaneous continuous acoustic masking did not affect the response and no facial nerve response was observed on the facial nerve monitoring. These features strongly suggest that the characteristic vertex-negative potential constitutes a specifically evoked response of the vestibular system. Electrophysiological monitoring of the sectioning of the vestibular nerve during operation is one possible clinical application of intraoperative recording of electrically evoked vestibular potentials.