Changes of Extra- and Intracochlear Electrocochleographic Responses During Insertion of the Cochlear Implant Electrode Array

Background: In human cochlear implant (CI) recipients, electrocochleographic (ECoG) responses have been recorded from extra- and intracochlear sites. However, further insight is needed to elucidate the implications of changes of ECoG responses during cochlear implantation.

Objective: The aim of this study was to monitor extra- and intracochlear ECoG responses during cochlear implantation and to correlate ECoG changes with postoperative hearing preservation.

Material and Methods: ECoG responses to 250, 500, 750 or 1000 Hz tone bursts or acoustic click stimuli were recorded during insertion of the CI electrode array. For extracochlear ECoG, a recording electrode was placed on the promontory. For intracochlear ECoG recordings, the most apical contact of the CI electrode array was used as recording electrode. Changes of ECoG recordings were correlated with pure-tone audiometric findings 4 weeks after surgery.

Results: Mean hearing loss in subjects without decrease or loss of extracochlear ECoG signals was 12 dB, compared to a mean hearing loss of 22 dB in subjects with a detectable decrease or a loss of ECoG signals (p = 0.0058, n = 51). If a permanent decrease of ECoG signals occurred during insertion of the CI electrode, the decrease was detectable during the second half of the insertion.

Conclusion: Decrease of extracochlear ECoG recordings during surgery has a significant correlation with hearing loss 4 weeks after surgery. Trauma to cochlear structures seems to occur during the final phase of the CI electrode insertion.