A prewarning sign for hearing loss by brainstem auditory evoked potentials during microvascular decompression surgery for hemifacial spasm.

OBJECTIVE: We aimed to define the prewarning sign of brainstem auditory evoked potentials (BAEPs) associated with cerebellar retraction (CR) during microvascular decompression surgery for hemifacial spasm. METHODS: A total of 241 patients with a latency prolongation of 1 ms or an amplitude decrement of 50% of wave V were analyzed. According to BAEPs before significant changes during CR, patients were classified into Groups A (latency prolongation of wave I [>/=0.5 ms] without prolongation of the I-III interpeak interval [<0.5 ms]) and B (no latency prolongation of wave I [<0.5 ms] with prolongation of the I-III interpeak interval [>/=0.5 ms]). BAEPs and postoperative hearing loss (HL) were compared between the two groups. RESULTS: Group B comprised 160 (66.4%) patients. With maximal changes in wave V, latency prolongation (>/=1 ms) with amplitude decrement (>/=50%) was more common in Group B (p < 0.018). At the end of the operation, wave V loss was observed in 11 patients, including 10 patients from Group B. Five patients developed postoperative HL; all were from Group B. CONCLUSIONS: Latency prolongation of wave III during CR was associated with serious BAEPs changes and postoperative HL. SIGNIFICANCE: Latency prolongation of wave III is a significant prewarning sign.