Intraoperative impedance and ECAP results in cochlear implant recipients with inner ear malformations and normal cochlear anatomy: a retrospective analysis.

Background: The intraoperative measurements are essential steps in cochlear implant (CI) surgery for confirming correct electrode placement.

Objectives: To examine the intraoperative impedance and electrically evoked action potential (ECAP) measurement results of cochlear implant (CI) users with normal cochlear anatomy (NCA) and to compare them with CI users with inner ear malformations (IEM).

Material and methods: This retrospective study included intraoperative data of 300 ears from 258 individuals using Medel^® and Cochlear (Nucleus^®) CI devices.

Results: Impedance values differed through all regions, and that differences in ECAPs results mainly stemmed from the basal region in Cochlear users, when comparing the impedance values and ECAPs recording prevalence between the NCA and IEM groups, it was observed that there was no significant difference in the impedance values across the intracochlear regions of the groups (apical; p = .26, middle; p = .12, basal; p = .99). However, it was found that the prevalence of measurable ECAPs in all intracochlear regions of the NCA group was higher than the IEM group (p = .000).

Conclusion and significance: The robustness of cochlear structures is a crucial factor in the recording of ECAPs. Furthermore, findings in the IEM group demonstrated that proper placement of intracochlear electrodes did not guarantee effective auditory nerve stimulation.