Multi-frequency Electrocochleography Measurements can be Used to Monitor and Optimize Electrode Placement During Cochlear Implant Surgery.

OBJECTIVE: To report the use of multi-frequency intra-cochlear electrocochleography (ECOG) in monitoring and optimizing electrode placement during cochlear implant surgery. An acoustic pure tone complex comprising of 250, 500, 1000, and 2000 Hz was used to elicit ECOG, or more specifically cochlear microphonics (CMs), responses from various locations in the cochlea. The most apical cochlear implant electrode was used as the recording electrode. STUDY DESIGN: Clinical capsule report. SETTING: Tertiary academic referral center. RESULTS: ECOG measurements were performed during cochlear implant surgery in an adult patient with significant residual acoustic hearing. The 500, 1000, and 2000 Hz CM tracings from the most apical electrode showed an amplitude peak at three different instances during the early phase of cochlear implant electrode insertion. These results are consistent with the tonotopic organization of the cochlea. During final electrode placement a slight advancement of the electrode array resulted in a correlated decrease in 250, 500, and/or 1000 Hz CM amplitude. The electrode array was retracted and repositioned which resulted in a recovery of CM amplitude. Intraoperative CM thresholds revealed a correlation of r = 0.87 with preoperative audiometric thresholds. CONCLUSION: We present a report on simultaneous multi-frequency ECOG monitoring during cochlear implant surgery. Multi-frequency ECOG can be used to differentiate between electrode trauma and the advancement of the apical electrode beyond the CM source in the cochlea.