889 Significance of Cortico-Bulbar Motor Evoked Potential (CoMEP) Monitoring in Vestibular Schwannoma Surgery for Prediction of Postoperative Facial Nerve Palsy

Abstract

INTRODUCTION: Direct facial nerve stimulation during vestibular schwannoma surgery (VSS) allows preservation of the nerve in its continuity. However, prognostication of post- operative nerve function remains challinging. METHODS: In total, 51 patients (median age 52yrs; 19-84) with unilateral VS (median size 20mm;10-50) were included. Intraoperative neuromonitoring consisted of auditory evoked potentials (AEPs), direct facial nerve stimulation and CoMEPs. An anodal stimulation via subdermal corkscrew electrodes on position C3 or C4 and a cathode near Cz with a train of 6 pulses, each with a duration ono 500us, at a frequency of 5000 Hz and an interstimulus-interval of 2 ms was used. RESULTS: Complete resection was achieved in >90% of patients. Preoperative hearing was preserved in 78% (40/51) patients and postoperative serviceable hearing was preserved in 35% (18/49) patients and was closely related to preserved wave V of the AEPs. Additionally, MEPs were successfully monitored in every patient for the entire duration of the surgery. In 16% of the patients, more than 50% reduction of MEP baseline amplitude was recorded, correlating directly with moderate to severe postoperative facial palsy (House Brackman 3-5). No facial palsy without MEP amplitude reduction was observed. During 6 months FU, recovery of 1-2 HB Grades was observed in all cases. All patients with intraoperative MEP amplitude reduction had significant larger VS than patients without MEP amplitude reduction (27 vs 22 mm, p = 0.02) CONCLUSIONS: In addition to direct facial nerve stimulation, intraoperative CoMEP monitoring during VSS seems to be of high significance and value for intraoperative facial nerve preservation and prognosis estimation of postoperative short- and long-term facial palsy.