1578 Advances in Facial Nerve Monitoring Parameters During Vestibular Schwannoma Surgery

Aim To evaluate the effectiveness of multi-channel electromyographic monitoring of the facial nerve in improving the detection of mechanically elicited EMG activity and providing new predictive criteria for post-operative facial nerve function. Method The Study was conducted on 20 patients undergoing vestibular schwannoma resection in a tertiary referral cerntre. All patients were subjected to facial nerve monitoring during the surgery by a 5-channel setup monitoring the frontalis, O.oculi, nasalis, O.oris, and mentalis muscle. Mechanically elicited EMG activities of the monitored facial muscles were recorded for analysis. After tumour removal, the facial nerve was stimulated proximal to the tumour site using two different types of probes: Prass and flush-tip. Post-operative facial nerve function was assessed using House-Brackmann scale immediately post-operatively and after six months and correlated to the study tested parameters. Results The use of 5-channel montage led to significantly higher sensitivity in detecting mechanically elicited EMG activity than would have been possible with the ordinary 2-channel one. Mentalis muscle showed significantly higher number and amplitude of spontaneous EMG activities than other facial muscles. Positive correlation was found between the proximal threshold and the post-operative facial nerve outcome. The Prass stimulator showed significantly lower threshold than the ball-tip probe. Conclusions The use of multi-channel facial nerve monitoring allowed earlier and more efficient monitoring of the facial nerve. The use of the Prass stimulator is more accurate and correlates more with the real threshold needed for post-resection stimulation of the facial nerve than the ball-tip.