Electromyographic evaluation of facial nerve damage in acoustic neuroma surgery

Objective: This study aimed to determine whether postoperative facial nerve paralysis or surgical manipulation causing paralysis could be predicted on train responses during intraoperative facial nerve monitoring in acoustic neuroma surgery. Study Design and Setting: This was a prospective study performed at a tertiary referral center. Patients and Methods: Train responses were recorded on a floppy disk and compared with postoperative facial nerve function in 51 patients who underwent enlarged translabyrinthine acoustic neuroma surgery. Main Outcome Measures: The number, duration, frequency, and peak-to-peak amplitude of train responses were analyzed and compared with postoperative facial nerve function. Results: Trains were observed in 42 of 51 patients. Six of seven patients with high-amplitude trains more than 250 muV, and three of five patients with bomber-type high-frequency trains elicited during tumor dissection from the facial nerve or stretching the nerve, showed severe facial nerve dysfunction. On the other hand, seven of the nine patients with no trains also showed severe facial nerve dysfunction. Conclusions: The presence of high-amplitude or high-frequency trains elicited by surgical manipulation to the facial nerve seems to indicate a critical situation for the facial nerve. However, certain types of mechanical trauma resulting in severe facial nerve paralysis cannot be identified by train responses.