Intra-operative monitoring of two facial muscles in hemifacial spasm surgery

Abstract Background Hemifacial spasm (HFS) is a chronic facial nerve disorder characterized by spontaneous muscle contractions. Microvascular decompression (MVD) is the neurosurgical treatment of choice. Intraoperative neurophysiologic monitoring (IOM) during MVD can help determine when adequate decompression is performed. Methods MVD with IOM was performed on 16 patients with HFS that included recording the abnormal lateral spread response (LSR) in lower facial muscles, considered as neurophysiologic marker of HFS. Two lower facial muscles were monitored as opposed to a standard monitoring of a single muscle. Results All patients underwent preoperative thin cut MRI confirming the presence of neurovascular conflict. Patients underwent small retrosigmoid craniotomy and MVD. In 13 cases, the LSR guided the surgeon to continue MVD until the response was unobtainable from all recorded lower facial muscles. In four of those (30%), the LSR persisted on one of the recorded muscle and prompted further exploration and decompression until complete disappearance of LSR in all recorded muscles. In two cases, the LSR disappeared after dural opening and never recurred during the procedure, therefore the completion of MVD was based on non reappearance of LSR. In one case, the LSR persisted despite apparent complete decompression of the nerve. Fourteen patients had complete relief of their symptoms after surgery, one had partial improvement and the one with persistent LSR was unchanged. Conclusion Evaluation of the LSR by monitoring of two lower facial muscles provides valuable neurosurgical guidance during MVD for HFS. This simple modification of intra-operative monitoring may improve prediction of satisfactory MVD and HFS resolution.