Intraoperative Tip Fold-Over Detection of Cochlear Implant Electrode Arrays by Spread of Excitation Measurements

Background

Intraoperative measurements after the insertion of the cochlear implant (CI) electrode array are common practice to objectify the integrity of the CI. The recording of thresholds of electrically evoked compound action potentials (T-ECAP) provides valuable information on the hearing nerve’s functionality while additional spread of excitation (SOE) measurements provide information on the electrodes’ positioning within the cochlea.

Objectives

This study investigates the use of SOE and T-EACP as an indicator for electrode tip fold-over.

Methods

During 221 implantations (CI512 and CI532; Cochlear Ltd.) of adult subjects, ECAP thresholds (AutoNRT) and SOE measurements were recorded intraoperatively. The probe electrode (#15) was stimulated above the electrodes T-ECAP. The measurement data was evaluated regarding N1-P1 amplitudes of the various masking electrodes and T-ECAPs in relation to tip fold-over cases approved by x-ray imaging and/or CT scan.

Results

T-ECAPs can be recorded for all electrodes in 96.6% of the implantations. Only 4 implantations (1.8%) did not exhibit T-ECAP on any electrode.

In total, eight cases of a tip fold-over occurred and all cases were detected by SOE measurements due to their increasing N1-P1 amplitudes towards the most apical masker electrode. Three tip fold-overs that occurred with the CI532 implant could be corrected immediately during surgery since this implant offers the possibility of a second insertion with a reloading tool.

Conclusions

SOE measures provide a powerful tool to objectify the array’s positioning within the cochlea without additional equipment in very little time. However, intraoperative imaging may sometimes still be required in case of immeasurable T-ECAPs or possibly inconclusive SOE results.