Emprical factors associated with Brainstem auditory evoked potential monitoring during microvascular decompression for hemifacial spasm and its correlation to hearing loss.

BACKGROUND: Cranial nerve VIII is at risk during microvascular decompression (MVD) for hemifacial spasm (HFS). The primary aim of this study is to evaluate the empirical factors associated with brainstem auditory evoked potential monitoring and its correlation to post operative hearing loss (HL) after MVD for HFS. METHODS: Pre-operative and post-operative audiogram data and BAEP from ninety-four patients who underwent MVD for HFS were analyzed. Pure tone audiometry (PTA) and Speech Discrimination Score (SDS) were performed on all patients before and after surgery. Intraoperative neurophysiological data were reviewed independently. HL was assessed using the AAO-HNS classification system for non-serviceable hearing loss (Class C/D), defined as PTA >50 dB and/or SDS <50% within the speech range of frequencies. RESULTS: Patients with HL had higher rates of loss in the amplitude of wave V and prolongation in the interpeak latency of peak I-V latency during MVD. Gender, age, side, and MVD duration did not increase the risk of HL. There was no correlation between successive number of BAEP changes (reflective of the number of surgical attempts) and HL. There was no association between the speed of recovery of BAEPs and HL. CONCLUSIONS: Patients with new post-operative HL have a faster rate of change in the amplitude of wave V and the interpeak I-V latency during intraoperative BAEP monitoring for HFS. Our alarm criteria to inform the surgeon about impending nerve injury might have to be modified and prospectively tested to prevent rapid change in BAEPs.