Cochlear Implant Insertion Routes and Intra-operative Electrophysiological Measurements: A Retrospective Analysis at a Tertiary Care Centre

Background: Cochlear implant surgeries are performed by different surgical routes, Round window (RW), Extended round window (Ext RW) and Cochleostomy (C). Optimum intracochlear electrode placement is important to achieve a successful outcome. Intra-operative electrophysiological testing (Impedance and ECAP) is crucial to assess the device function and appropriate electrode placement. The variability of portal of electrode insertion might affect the neural response and its characteristics. Objective: To compare the intraoperative electrophysiological measurements (Impedance and ECAP) for possible differences on auditory nerve stimulation across the three electrode insertion routes. Materials and Methods: This is a retrospective data analysis of 47 cochlear implant recipients at a tertiary care centre in Central India over a period of 4 years. They were broadly divided into two groups depending on the electrode design as full banded and half banded. Intraoperative impedances were recorded for different modes of stimulation and ECAP measured at E5, E10, E15, E20 electrodes in both the groups across the three insertion routes. Results: In the half-banded group, the impedance values in different modes CG, MP1, MP2, MP1 + 2 did not differ significantly among the surgical routes at all four electrodes. While in the full banded group, for CG mode impedance values at E5 differ significantly. Rest for other modes in full banded group, there was no statistically significant difference across the three routes. Conclusion: The present study supports that there is no statistically significant difference in the intraoperative impedance and ECAP measurements in both, the full-banded and half- banded electrodes across the three surgical routes implying that, all the three surgical approaches provide equal stimulation of the auditory nerve. The CI surgeon can select the electrode insertion portal based on the surgical anatomy, the implant type and individual preferences.