Intraoperative auditory monitoring in vestibular schwannoma surgery: new trends

OBJECTIVE: To investigate the efficiency of a new method of brainstem auditory-evoked potential (BAEP) monitoring during complete vestibular schwannoma (VS) resection with attempted hearing preservation. MATERIAL AND METHODS: Dedicated software providing near real-time recording was developed using a rejection strategy of artifacts based on spectral analysis. A small sample number (maximum 200) is required and results are obtained within 10 s. Fourteen consecutive patients with hearing class A operated on for VS, in an attempt to preserve hearing, participated in the investigation. Postoperatively, 7 patients (50%) had useful hearing (hearing class A, 4/14; hearing class B, 3/14) on the operated side. Seven patients (50%) were reduced to hearing class D. RESULTS: Drilling of the internal auditory canal (IAC) and tumor removal at the lateral end of the IAC were identified as the two most critical steps for achieving hearing preservation. Intraoperative BAEP monitoring was sensitive in detecting auditory damage with useful feedback but its effectiveness in preventing irreversible hearing impairment was not demonstrated in this study. CONCLUSION: Combined BAEP and direct auditory nerve monitoring using the same equipment will be performed in the future in an attempt to enhance the chances of preventing irreversible hearing damage, and possibly to improve the hearing outcome significantly