Abstract
Experience in the use of intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) to relieve hemifacial spasm (HFS) in 42 patients is reported. No patient was deaf before surgery. Postoperatively, one patient (2.3%) was totally deaf. Mean preoperative pure tone average (PTA) was 12.5 ± 9.2 dB. Mean postoperative PTA was 20.5 ± 18 dB (p<0.001). The wave I–V interval was elevated in 5 patients preoperatively and in 12 patients postoperatively. The postoperative BAEPs of the patient who became deaf were totally and definitely obliterated. During surgery changes in BAEPs were as follows: after anesthetic induction the mean I–V interval was significantly increased compared to the preoperative recordings (p<0.001). In 5 patients retraction of the cerebellum led to either abolition of waves (transient in 4 cases, permanent in 1 case), which required removal or repositioning of the retractor, or to a significant delay of peak V (29 cases) or no change (8 cases). Microvascular decompression procedure led to transient abolition of all waves (4 cases) or to the abolition of all waves except peak I (4 cases) or to delays of peak V ranging from 0.5 ms to > 1 ms (18 cases). In 15 cases changes were negligible. The main concern in BAEP monitoring was to identify significant changes of the response waveform, latencies and amplitudes on-line, and to give functional warnings to the surgeon so that he or she could modify his or her maneuvers and thus prevent deterioration of the auditory pathway. It is concluded, as it has been in other studies, that intraoperative BAEP monitoring during microvascular decompression to relieve HFS reduces the risk of postoperative deafness.