Estimating Performance Using Tonotopic Measurements of Intracochlear Electrocochleography: Comparison of Lateral Wall and Perimodiolar Arrays

OBJECTIVE: To assess intracochlear electrocochleography (ECochG) for estimating cochlear implant (CI) performance for lateral wall and perimodiolar electrode arrays. STUDY DESIGN: Prospective cohort study. SETTING: Tertiary referral center. METHODS: From December 2021 to June 2024, ECochG was measured intraoperatively using the Active Insertion Monitoring (AIM) system by Advanced Bionics. After insertion, multifrequency tone bursts were delivered via a sound tube from 250 Hz to 2 kHz at 95 to 105 dB HL with recordings at each internal electrode. Using spectral analysis, the maximal amplitude (MA) response electrode was identified by frequency and summed into a single value of total response (MA-ECochG-TR). Postoperative CI performance was routinely monitored. RESULTS: Of 57 participants with ECochG recordings, 43 completed 6-month testing. Of these, 23 were perimodiolar (Mid-Scala [MS]), and 20 were lateral wall (SlimJ [SJ]). MA-ECochG-TR had a moderately strong positive correlation to 6-month consonant-nucleus-consonant (CNC) word scores for MS cases (r = 0.73, 95% CI [0.46-0.88], P < .001), but showed no significant correlation for SJ cases (r = 0.04, 95% CI [-0.41 to 0.47], P = .87). For the 13 SJ recipients without electroacoustic stimulation (EAS), there was a moderate, non-significant positive correlation between MA-ECochG-TR and 6-month CNC (r = 0.44, 95% CI [-0.14 to 0.80], P = .13). CONCLUSION: MA-ECochG-TR independently estimates performance for perimodiolar arrays. Intracochlear ECochG is less predictive for lateral wall arrays; this may be due to confounding from EAS (though this was not statistically significant) or from signal degradation with a larger electrode-modiolar distance.