OBJECTIVE The purpose of this study was to evaluate whether intraoperative monitoring of lateral spread response (LSR) improves the efficacy of microvascular decompression (MVD) for hemifacial spasm (HFS). METHODS In this prospective study, patients undergoing MVD for HFS were assigned to one of 2 groups, Group A (MVD with intraoperative LSR monitoring) or Group B (MVD without LSR monitoring). Clinical outcome at 12 months after surgery was assessed through telephone survey. Data analysis was performed to investigate the effect of intraoperative LSR monitoring on efficacy of MVD. RESULTS A total of 283 patients were enrolled in the study, 145 in Group A and 138 in Group B. There was no statistically significant difference between the 2 groups with respect to the percentage of patients who had spasm relief at either 1 week (Group A 87.59% vs Group B 83.33%; p = 0.317) or 1 year (93.1% vs 94.2%; p = 0.809) after surgery. A clear-cut elimination of LSR during surgery was observed in 131 (90.34%) of 145 patients; LSR persisted in 14 patients (9.66%) at the end of the surgical procedure. Disappearance of LSR correlated with spasm-free status at 1 week postoperatively (p = 0.017) but not at 1 year postoperatively (p = 0.249). CONCLUSIONS Intraoperative LSR monitoring does not appear to provide significant benefit with respect to the outcome of MVD for HFS in skilled hands. Persistence of LSR does not always correlate with poor outcome, and LSR elimination should not be pursued in all patients after verification of complete decompression.
Keywords: EMG = electromyographic; HFS = hemifacial spasm; LSR = lateral spread response; MVD = microvascular decompression; REZ = root exit zone; functional neurosurgery; hemifacial spasm; intraoperative monitoring; lateral spread response; microvascular decompression.