Intra-operative test electrode and electrical auditory brainstem response after preoperative assessment in cochlear implant candidacy

Introduction: Over the last years, in doubt of cochlear implant (CI) candidacy, assessment of excitability of the auditory nerve is performed with pre-operative tests. These tests are the pre-operative (pre-op.) performed electrical auditory brainstem (EABR) and the late response (EALR) recorded with trans-tympanic promontory stimulation in local anesthesia. But in some cases after such preoperative tests there is still doubt about the excitability of the auditory pathway. The most reliable EABR is recorded with using stimulation via the CI. However, before CI implantation,, an intra-cochlear test electrode could be used in order to achieve similar EABR results. Methods: In doubtful cases of patients who underwent pre-op. EABR, we performed EABR by a test electrode, part of the auditory nerve test system. This measurement was used to confirm the pre-operative results just before CI implantation. Additionally, EABR using CI stimulation was performed intra-operatively right after the CI implantation to confirm EABR using the test stimulation electrode results. Results: Six subjects were included in this study. They were tested by pre-op. EABR (n=6), pre-op. EALR (n=5), intra-op. EABR using test electrode (n=6), intraop. EABR via CI (n=6), and post-op. EABR (n=2), and postop. EALR (n=2). In two cases, intra-operative EABR showed a positive, i.e. clearly measureable, response whereas there was a doubtful response in pre-op. EABR. Intra-op. EABRs (test electrode and CI stimulation) showed the same results in all cases. Waveforms of EABR using test electrode look similar to EABR using CI stimulation but with more defined peaks compare to the pre-op. EABR. In one case with all-over positive EABR, pre-op. EALR, and post-operative EALR were matching. Conclusion: Intra-op. EABR using test electrode was easy to record and it shows similar results to EABR using CI stimulation. Intra-op. EABR using test electrode may help in confirming the results of not clear preop. EABR with a minimal increase in recording time