Application of brain-stem auditory evoked potential to prevent the hearing impairment in microvascular decompression for hemifacial spasm

Objective To investigate the usefulness of brain-stem auditory evoked potential(BAEP)to decrease the danger of hearing impairment for the patients with hemifacial spasm in the process of microvascular decompression.Methods We obtained the intraoperative BAEP data of 43 patients with hemifacial spasm between Dec 2004 and Aug 2005.These patients accepted pure tone average(PTA) before and after the operations.They were divided into two groups depending on the changes of the PTA examination values which were less than 20dB or not and compared pre-and post-operation.The changes in waveⅤlatency were analyzed and compared with the changes in the PTA values,in order to deduce the warning values for the delay of the waveⅤlatency.ResultⅤlatency was significantly delayed at the time of exposure and manipulation of the offending vessels.There were 38 patients in group one with the PTA values increased less than 20dB,and the remaining 5 patients in the group two with the PTA values increased more than 20dB.The mean delays in waveⅤlatency of group one was(0.60±0.43) ms,and group two was (1.07±0.35) ms.There were difference between two groups compared with the 0.6ms delays, and there were significant difference between two groups compared with the 1.0ms delays.Therefore 0.6ms and 1.0ms were analyzed statistically as two warning values of the delays in waveⅤlatency during the operations.Conclusion Intraoperative BAEP monitoring provides useful information to guide the MVD operations in order to protect the audio function of the patients with hemifacial spasm.