Evaluation of the Functionality of the Cochlear Nerve in Patients with Vestibular Schwannoma

Background: Cochlear implantation is an emerging indication for patients with a vestibular schwannoma (VS), especially NF2 patients. In these cases, it may be necessary to assess the viability of the cochlear nerve in order to predict the outcome of a cochlear implant (CI).

Objective: The aim of this talk is: (1) To assess the functionality of the auditory nerve in standard cochlear implantees by using an intracochlear test electrode, comparing electrical auditory brainstem responses (eABR) via the test electrode with the eABR responses with the CI. (2) To assess the usefulness of this intraoperative electrode in VS patients

Methods: Main outcome measures were the quality of an eABR waveform, scoring criteria from Walton et al. and postimplantation audiometric scores

Results: (1) Of 10 postlingually deaf patients, it was possible to evoke electrical stimulation responses along with both the test electrode and the CI in all subjects. No significant differences in latencies or amplitudes after stimulation were found between the test electrode and the CI. All subjects obtained useful hearing with their CI and use their implants daily

(2) Of 21 patients with a VS, 16 were implanted, 14 of them achieving auditory perception. According to the test electrode there was one false positive and one false negative case.

Conclusions: The intracochlear test electrode may be a suitable method to test the integrity of the auditory nerve by recording eABR signals. In selected patients, this may allow for cochlear implantation as an alternative to ABI.