Intraoperative electrophysiological monitoring in microvascular decompression for hemifacial spasm

We aimed to determine the reliability of (i) intraoperative monitoring by stimulated electromyography (EMG) of the facial nerve to predict the completeness of microvascular decompression (MVD) for hemifacial spasm (HFS), and (ii) brainstem auditory-evoked potential (BAEP) to predict postoperative hearing disturbance. We conducted a prospective study of 36 patients who received MVD for HFS. We confirmed the disappearance of an abnormal muscle response in the facial nerve EMG to predict the completeness of MVD, and performed BAEP monitoring to predict postoperative hearing disturbance. The sensitivity, specificity and accuracy of facial nerve EMG and BAEP monitoring were evaluated. The sensitivity, specificity and accuracy of facial nerve EMG were 0.97, 1.0 and 0.97, respectively, and that for BAEP monitoring were 1.0, 0.94 and 0.94 respectively. There was one false positive result for facial nerve EMG, and two false positive results for BAEP monitoring. No false negative result was encountered for either EMG or BAEP monitoring. Facial nerve EMG correctly predicted whether MVD was successful in 35 out of 36 patients, and BAEP correctly predicted whether there was postoperative hearing disturbance in 34 out of 36 patients. Intraoperative facial nerve EMG provides a real-time indicator of successful MVD during an operation while BAEP monitoring may provide an early warning of hearing disturbance after MVD.