| Summary: | <p><strong>Objective </strong>To investigate the significance of abnormal muscle response (AMR) monitoring during microvascular decompression (MVD) for hemifacial spasm (HFS) in confirming the responsible blood vessel, improving the prognosis and reducing postoperative complications. <strong>Methods</strong> A total of 34 HFS patients underwent AMR monitoring during MVD. <strong>Results </strong> The AMR of mentalis was recorded in all 34 patients by electrically stimulating zygomatic branch of facial nerve before anesthesia. Compared with preoperation, the AMR latency after operation was significantly longer [(16.12 ± 3.17) ms vs (14.75 ± 3.32) ms, P = 0.015] and amplitude was significantly reduced [(0.11 ± 0.03）mV vs (0.13 ± 0.03) mV, <em>P</em> = 0.027]. AMR was disappeared in 32 cases (94.12% ) after the removal of responsible blood vessel. There was one patient (2.94%) whose AMR disappeared momentarily after the incision of endocranium and disappeared completely after the removal of responsible blood vessel, while AMR still existed in one case (2.94%) after the removal of responsible blood vessel. Responsible blood vessels included anterior inferior cerebellar artery (N = 30, 88.24%), posterior inferior cerebellar artery (N = 3, 8.82%) and basilar artery (N = 1, 2.94%), which oppressed the root of facial nerve (N = 22, 64.71%), the distal part (N = 8, 23.53%), and both the root and distal part (N = 4, 11.76%). After operation, facial spasm disappeared. Thirty-one cases were cured, 2 cases evidently remitted, and one case inefficacious. The total effective rate was 97.06%. <strong>Conclusions</strong> Continuously intraoperative monitoring of AMR contributes to confirming the responsible blood vessel, completing decompression for facial nerve more thoroughly, improving the prognosis, reducing delayed healing up, at the same time enhancing neurosurgeons' confidence and reducing operation time.</p><p> </p><p><strong>DOI: </strong>10.3969/j.issn.1672-6731.2016.05.010</p>
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