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OBJECTIVE: In a common cavity (CC) deformity, the cochlea and vestibule are confluent to form a single cavity without internal architecture, and distribution of auditory neuronal tissue is unclear. The purposes of this study are to reveal the spatial distribution of auditory neuronal tissue in CC deformity using electrically evoked auditory brainstem response (EABR) during cochlear implantation. STUDY DESIGN: Retrospective case review. SETTING: Cochlear implant (CI) center at a tertiary referral hospital. PATIENTS: Five patients with CC deformity who underwent cochlear implantation and intraoperative EABR testing. MAIN OUTCOME MEASURES: Spatial distribution of electrodes that elicited an evoked wave V (eV) in EABR testing was evaluated in each CC deformity. RESULTS: Electrically evoked auditory brainstem response testing demonstrated that electrodes attached on the inner wall of the anteroinferior cavity of the CC deformity successfully elicited a reproducible eV in all cases, and the latency of each eV was an approximately 4 ms, which is similar to those reported in patients without an inner ear malformation. Interestingly, in Case 1 with the lowest percentage of eV-positive electrodes (31.8%), CI-aided audiometric thresholds were changed, depending on the frequency allocation to eV-positive electrodes in the programming. Cochlear implant-mediated facial nerve stimulation was observed in 3 of 5 cases, and results of EABR testing were useful for optimizing the device program to decrease facial nerve stimulation without sacrificing CI-mediated auditory performance. CONCLUSION: The results of EABR testing suggested that auditory neuronal elements are distributed to the anteroinferior part of CC deformity, mainly around or near the inner wall of the cavity. In cases with CC deformity, EABR testing is useful to achieve the optimal electrode array placement and to adjust programming parameters of the implanted device, which might be essential to maximize CI outcomes and to decrease facial nerve stimulation.
Yamazaki et al. (Fri,) studied this question.