Electrocochleography Observations In A Series Of Cochlear Implant Electrode Tip Fold-Overs

Objective: Tip fold-over is a rare but serious complication of cochlear implant (CI) surgery. The purpose of this study was to present intraoperative electrocochleography (ECochG) observations in a series of CI electrode tip fold-overs. Patients: Five pediatric subjects undergoing CI surgery through a round window (RW) approach with a perimodiolar electrode array, who were diagnosed with either auditory neuropathy spectrum disorder or enlarged vestibular aqueduct. Interventions: Intraoperative RW ECochG during CI surgery: tone burst stimuli were presented from 95 to 110 dB SPL. Main Outcome Measure(s): Magnitude and phase characteristics of ECochG responses obtained intraoperatively before and immediately after electrode insertion were examined for patients with and without tip fold-over. Results: Three subjects presented with tip fold-over and two formed the control group. Among fold-over cases, one participant exhibited an inversion in the starting phase of the cochlear microphonic response and a decrease in spectral magnitude from pre- to postinsertion. Both subjects who did not exhibit a change in phase had an increase in the ECochG-total response (ECochG-TR) magnitude. No case in the control group exhibited a change in starting phase. In regard to the ECochG-TR, all controls showed a decrease in the magnitude. Conclusions: Despite the small number of patients, heterogeneous ECochG response patterns were observed within the fold-over group. Though these results are not conclusive, they can serve as a framework to begin to understand ECochG's utility in detecting intraoperative tip fold-over.