INTRAOPERATIVE FACIAL-NERVE MONITORING IN ACOUSTIC NEUROMA SURGERY

Intraoperative facial nerve monitoring simultaneously using electromyo graphy and mechanical pressure sensors is being used in retrosigmoid a nd translabyrinthine approaches for acoustic neuroma resection. Insula ted electrified microsurgical instruments and air drills are used to s timulate the facial nerve with a pulsed, constant current through bone and tumor, before the facial nerve is visually encountered. Electrica l stimulation is used to help locate the facial nerve, map the course of the facial nerve within tumor, warn the surgeon of unexpected facia l nerve locations, and help predict facial nerve function postoperativ ely. In 57 unmonitored cases a House-Brackmann (H-B) grade I or II res ult was obtained in 77 percent of small, 81 percent of medium, and 60 percent of large tumors. In 64 monitored cases H-B grade I or II was o btained in 88 percent of small, 79 percent of medium, and 90 percent o f large tumors. Overall, facial nerve outcomes were better after monit ored procedures (p < 0.02). A modified H-B classification for acute fa cial nerve injury is introduced to grade facial weakness immediately p ostoperatively and until function is stable at 1 year. In the unmonito red group there were five (9%) cases with a complete facial paralysis, facial nerve intact (i.e., acute H-B grade VI(A)) and seven (13%) cas es with the facial nerve transected (i.e., acute H-B grade VI(B)). In the monitored group there were five (8%) acute H-B grade VI(A) and two (3%) acute H-B grade VI(B) results. In the unmonitored group of large tumors, there were statistically more patients with an acute H-B grad e VI(B) result (p < 0.05). The evolution in techniques and results of intraoperative facial nerve monitoring are presented.