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Role of Facial Nerve Motor-Evoked Potential Ratio in Predicting Facial Nerve Function in Vestibular Schwannoma Surgery Both Immediate and at 1 Year

Bhimrao, Sanjiv K.; Le, Trung N.; Dong, Charles C.; Makarenko, Serge; Wongprasartsuk, Sarin; Westerberg, Brian D.; Akagami, Ryojo

doi: 10.1097/MAO.0000000000001137
TUMORS OF THE EAR AND CRANIAL BASE
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Objective: To determine whether transcranial electrical stimulation-induced facial motor-evoked potential (FMEP) monitoring of the facial nerve (FN) during vestibular schwannoma (VS) tumor resection can predict both immediate and 1 year postoperative FN functional outcome.

Design: Prospective consecutive non-comparative observational case series.

Setting: Tertiary referral center.

Main Outcome Measures: Facial function, immediate post operation and at 1 year using House–Brackmann (HB) grading scale.

Methods: The study included 367 consecutive patients (men 178; women 189; age 13–81 years) monitored during primary sporadic VS microsurgery between November 2002 and April 2015. Neurofibromatosis type II, revision surgery, previous radiotherapy treatment, preoperative facial nerve weakness, and non-VS cases were excluded retrospectively during analysis of data. Data of facial function were missing from eight patients at 1 year and were excluded. The correlation between the final-to-baseline FMEP ratio and immediate and 1 year facial nerve function was examined.

Results: Using logistic regression model, the cut-off points of FMEP ratio were 0.62 (PPV 0.96) and 0.59 (PPV 0.98) which predicted satisfactory FN function (HB grades 1 or 2) immediately postoperative and at 1 year after surgery, respectively.

Conclusion: Transcranial electrical stimulation FMEP is a valuable tool for monitoring facial nerve function during resection of vestibular schwannoma. Maintaining a FMEP event-to-baseline ratio of 60% or greater is predictive of satisfactory long-term FN function.

*Division of Otolaryngology–Head & Neck Surgery

Division of Neurosurgery, Department of Surgery, University of British Columbia, Vancouver, British Columbia, Canada

Address correspondence and reprint requests to Ryojo Akagami, B.Sc., M.D., M.H.Sc., F.R.C.S.C., Division of Neurosurgery, Department of Surgery, Vancouver General Hospital, Vancouver Coastal Health Research Institute, University of British Columbia, Vancouver, BC, Canada V5Z 1M9; E-mail: Ryojo.Akagami@vch.ca

Sanjiv K. Bhimrao, Trung N. Le are co-first authors.

Funding: None.

The authors disclose no conflicts of interest.

Copyright © 2016 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company