Results of auditory brainstem response monitoring of microvascular decompression: A prospective study of 22 patients with hemifacial spasm

OBJECTIVES/HYPOTHESIS: The nerve function of cranial nerve VIII is at risk during microvascular decompression (MVD) for hemifacial spasm. Intraoperative monitoring of auditory brainstem response (ABR) is a useful tool to decrease the danger of hearing loss. The purpose of this study was to assess the side effects of MVD on hearing and describe the main intraoperative ABR changes observed in the authors' series. STUDY DESIGN: A prospective consecutive case series was performed. METHODS: The study includes 22 patients who underwent MVD with monitoring of ABRs. The latency prolongation and wave loss were analyzed at each surgical step, which were decided arbitrarily. Patients were divided into four groups depending on degree of change of wave V. Group 1 consisted of minimal change, whereas group 4 was permanent loss of wave V. Hearing changes were evaluated in 20 patients in the four groups who were available for postoperative hearing results. RESULTS: Loss of wave I, III, and V occurred with 6%, 13%, and 9% of surgical actions, respectively. Wave III disappearance was identified as the earliest and most sensitive sign and was usually preceded by the disappearance of wave V. The greatest prolongation of wave V at more than 1.0 ms developed statistically significant sensorineural hearing loss in the range of 10 dB. One patient in group 4 experienced deafness. CONCLUSIONS: In addition to the significant delay of wave V, useful recognition of early changes of wave III is possible and enables a change of microsurgical maneuvers to favor ABR recovery. Laryngoscope, 2009.