Electrocochleography during Cochlear Implantation for Hearing Preservation

Objective. To determine whether intraoperative electrocochleography during cochlear implant surgery provides online feedback to modify surgical procedure, reduce trauma, and increase preservation of residual hearing. Study Design. Prospective cohort study. Setting. Tertiary referral center, Otolaryngology Department, University of Verona. Subjects and Methods. Twenty-seven adult patients undergoing cochlear implant surgery who had low- to mid-frequency (0.25-2 kHz) auditory thresholds measured preoperatively were enrolled. Fifteen subjects had compound action potentials measured to assess cochlear function during surgery. In those patients, surgery was modified according to electrocochleographic feedback. Twelve control subjects underwent cochlear implant surgery with blinded electrocochleographic monitoring. Results. The average preoperative pure-tone audiometry thresholds (0.25-2 kHz) were 74.3 +/- 10.2 and 81.5 +/- 12.7 dB hearing level (HL) in the electrocochleographic feedback and control cohorts, respectively (P > .05). Compound action potential recordings showed a mean maximum latency shift of 0.63 +/- 0.36 ms and normalized amplitude deterioration of 59% +/- 19% during surgery. All of these changes reverted to normal after electrode insertion in all but 1 subject in the electrocochleographic feedback group. The average shifts in postoperative pure-tone average threshold (0.25-2 kHz), evaluated before activation, were 8.7 +/- 4.3 and 19.2 +/- 11.4 dB HL in the electrocochleographic feedback and control cohorts, respectively (P = .0051). Complete hearing preservation (loss of <= 10 dB) at 1 month before activation was achieved in 85% (11/13) of electrocochleographic feedback subjects and in 33% (4/12) of control patients (P = .0154). Conclusion. Monitoring cochlear function with electrocochleography gives real-time feedback during surgery, providing objective data that might help in modifying the surgical technique in ways that can improve the rate of hearing preservation.