Application of transcranial electrical stimulation-facial nerve motor evoked potentials in resection of large acoustic neuromas

Abstract

Objective To discuss the role of transcranial electrical stimulation facial nerve motor evoked potentials (TCE-FNMEP) in resection of large acoustic neuromas. Methods In a retrospective clinical study, 58 patients with large acoustic neuroma were investigated at Department of Neurosurgery, Tianjin HuanHu Hospital form July 2016 to March 2017.All patients were investigated by facial nerve motor evoked potentials elicited by multi-pulse transcranial electrical motor cortex stimulation. For recording, the same electrode set-up was used as for continuous EMG (electromyogram) monitoring of the orbicularis oculi, oris muscles and mentalis. Pre-surgical (dura opening), intraoperative and post-surgical (dura closing) TCE-FNMEP amplitudes and latencies were documented. End (dura closing) to start (dura opening) amplitude ratios were compared to early-term (1 day post surgery) facial nerve function by House-Brackmann (H-B) grading. Results Fifty-one (87.9%, 51/58) patients obtained total tumor resection and 7 (12.1%, 7/58) achieved subtotal resection. All patients had anatomical preservation of facial nerves. There was no death in this series. Reliable TCE-FNMEPs were obtained in all patients. At 1 day post operation, 48 out of 58 case were graded as H-B Ⅰ-Ⅱ, the range of TCE-FNMEP amplitude ratio was 47.6%-100.0%, and the median was 85.4%. Five cases were graded as H-B Ⅲ, the range of TCE-FNMEP amplitude ratio was 43.2%-55.8%, and the median was 45.4%. Three cases were graded as H-B Ⅳ, the range of TCE-FNMEP amplitude ratio was 31.4%-53.2%, and the median was 33.6%. Two cases were graded as H-B Ⅴ-Ⅵ, the range of TCE-FNMEP amplitude ratio was 6.1% and 11.3%, respectively. There was a negative correlation between TCE-FNMEP amplitude ratio and early post-surgical HB grading (r=-0.611, P<0.01). Conclusion TCE-FNMEP seems to be highly reliable in predicting early postoperative facial function in resection of large acoustic neuromas and could be a valid protection technique of facial nerve. Key words: Neuroma, acoustic; Facial nerve; Evoked potentials, motor; Transcranial electrical stimulation