An Investigation into the Site of Iatrogenic Auditory Impairment in Vestibular Schwannoma Surgery: A Pilot Study.

During vestibular schwannoma surgery a large proportion of patients will lose their hearing. While there have been several papers investigating the mechanism behind this loss of auditory function, the exact pathophysiological mechanisms remain relatively elusive. The present study aimed to document the patterns of electrophysiological auditory responses during retrosigmoid vestibular schwannoma surgery. In particular, we aimed to determine whether the site of auditory impairment in individual cases was predominantly cochlea or neural. Auditory function was monitored intraoperatively in two patients who underwent unilateral vestibular schwannoma surgery via the retrosigmoid approach at St George’s Hospital in Christchurch, and Dunedin Public Hospital. A combination of electrocochleography and direct eighth nerve monitoring techniques were used to monitor the auditory evoked potentials from the cochlea and cochlear nerve during the course of the surgery. Auditory brainstem response recordings were obtained from the second participant due to the technical difficulties in the primary electrophysiological techniques. Technical difficulties faced during the surgical procedure prevented the recording of both electrocochleography and direct eighth nerve monitoring potentials from each of the participants. As a consequence of this, we were unable to draw any conclusions about the site of iatrogenic injury in each surgery. Despite the insufficient recordings of auditory function, the technical and practical knowledge acquired during the course of this pilot study has established a foundation upon which the continuing research may build