Usefulness of electrical auditory brainstem responses to assess the functionality of the cochlear nerve using an intracochlear test electrode

[Objective]: To use an intracochlear test electrode to assess the integrity and the functionality of the auditory nerve in cochlear implant (CI) recipients and to compare electrical auditory brainstem responses (eABR) via the test electrode with the eABR responses with the CI.
[Setting]: Otolaryngology department, tertiary referral hospital.
[Patients]: Ten subjects (age at implantation 55 yr, range, 19–72) were subsequently implanted with a MED-EL CONCERTO CI on the side without any useful residual hearing.
[Interventions]: Following identification of the round window (RW), the test electrode was inserted in the cochlea previous to cochlear implantation.
[Main Outcome Measures]: To assess the quality of an eABR waveform, scoring criteria from Walton et al. (2008) were chosen. The waveforms in each session were classified by detecting waves III and V by the algorithm and visual assessment of the waveform. Speech performance was evaluated with monosyllables, disyllables, and sentence recognition tests.
[Results]: 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.
[Conclusions]: The intracochlear test electrode may be suitable to test the integrity of the auditory nerve by recording eABR signals. This allows for further research on the status of the auditory nerve after tumor removal and correlation with auditory performance.