AMR monitoring in microvascular decompression for hemifacial spasm: 115 cases report

•AMR monitoring was used in our series and provide valuable information to MVD operation for HFS.•Based on the electrophysiological results, the process of the operation can be adjusted.•With the information provided by AMR monitoring, precise exposure was more practicable and excessive dissection was avoided.•Microscope and endoscope were used alternately as was needed. In MVD operations assisted by AMR monitoring, the reliability and validity of decompression can be evaluated by observing whether AMR disappears. Although intraoperative AMR monitoring has been used widely, debate exists over its reliability and positive contribution. In this series, 115 cases of HFS treated with MVD operations with AMR monitoring were enrolled. All MVD procedures were performed via a suboccipital retrosigmoid approach. Microscope and endoscope were used alternately as was needed. Medtronic Nim-eclipse system was used for intra-operative AMR monitoring. The zygomatic branch of the facial nerve was stimulated and AMRs were recorded form the mentalis muscle. In 112 of the 115 cases, AMR was recorded during operation. In the 112 cases with typical AMR, AMR disappeared in 105 cases. Among the 105 cases, 79 achieved immediate cure after operation, 21 were spasm-free within 6-month follow-up, and the symptom of 5 cases persisted at 6-month follow-up. Among the 7 cases whose AMR did not disappear at the end of operation, 2 cases achieved immediate cure and 2 cases achieved delayed relief. For those cases with electrophysiological relief, the overall relief rate was 95.2% (100/105); for those with persistent AMR, the overall relief rate was 57.1% (4/7, P