Intracochlear Recording of Electrocochleography During and After Cochlear Implant Insertion Dependent on the Location in the Cochlea.

The study analyzed six patients retrospectively, so it cannot show that ECochG monitoring improves hearing preservation. Two patients were placed in each insertion-depth group, so the group differences are very small. The recording contact moved during insertion, and the expected signal pattern for optimal hearing preservation was not known. Amplitude drops could come from the contact moving past the response site, temporary basilar membrane blockage, or trauma, and these were not separated cleanly. Electrode position and frequency location were estimated from CT tracing and model assumptions, not directly observed function. Intraoperative visual interpretation differed from later quantitative analysis, so real-time decisions may be inaccurate. Noise floor was based on 10 data sets from an earlier study, not the current patients. Postoperative stimulation level may have been adjusted, so quantitative comparison at six months was limited. ECochG and hearing thresholds measure different things, so preserved responses do not guarantee preserved hearing.

The authors declared no potential conflicts of interest. Funding was from the Deutsche Forschungsgemeinschaft. The study used MED-EL implants and clinical software.

Do not conclude that a drop in intracochlear ECochG amplitude proves cochlear trauma. The recording site moved during insertion, and a drop could also reflect that the contact moved past the 500 Hz response site or a temporary mechanical event. The study analyzed six patients retrospectively.