Abnormal muscle response in microvascular decompression of hemifacial spasm.

In 1976, Jannetta et al, suggested that microvascular compression caused by arteries and veins crossing the root entry zone of the facial nerve, was the major etiology of hemifacial spasm (HFS). Surgical treatment has become a major trend. Microvascular decompression (MVD) with teflon patches has a high cure rate. However, the possible occurrence of multiple vessel compression makes it difficult to decide which of these vessels are responsible for the symptom during operation. Recently, a method of abnormal EMG was elaborated upon by Møller and Jannetta in 1987, to ensure the quality of MVD intraoperatively. In this study, we report 6 cases who underwent the procedure successfully. After general anesthesia and muscle relaxation, the abnormal EMG was not suppressed. When the offending vessel was lifted up from the facial nerve, the abnormal EMG disappeared immediately. In each case, postoperative improvement of facial spasm correlated with intraoperative abnormal EMG changes. This method is not only able to guide the surgeon to the vessel that induces HFS but also guarantees the quality of MVD.