Auditory Monitoring in Vestibular Schwannoma Surgery: Intraoperative Development and Outcome

Objective: The auditory brainstem response (ABR) may be a predictor of postoperative cochlear nerve function. In this study, the course of intraoperative ABR monitoring was analyzed to find predictive markers for postoperative hearing function.

Patients and methods: From 2010 to 2012, 46 patients who had had vestibular schwannoma surgery were investigated by intraoperative ABR monitoring. The type of ABR development was identified: type A, improved or stable ABR; type B, fluctuating or deteriorated ABR; and type C, slow or sudden ABR loss. Hearing function was correlated with ABR monitoring.

Results: The different types of ABR development showed a strong correlation with postoperative hearing (P < 0.001). ABR quality after 60% tumor removal was independently significant for hearing outcome. Possible interpretations are: 1) Independent of positive factors at the start of surgery at the final phase of tumor resection, what mattered for hearing outcome was the ABR quality (P < 0.001). 2) Dependence on ABR quality in the last phase might be a result of what the cochlear nerve has endured during resection. 3) The importance of ABR quality in the last phase might be because the tumor capsule is dissected from the nerves in that final phase.

Analysis: of critical actions with incidence of ABR impairment showed that dissection in the internal auditory canal and drilling were most critical.

Conclusions: Intraoperative ABR development is a predictive factor for postoperative hearing outcome. Deterioration should be avoided, because ABR improvement as a result of good status at the beginning of surgery could not be assumed.