Sequential Bilateral Cochlear Implantation via the Transmastoid Labyrinthotomy Approach Using Custom-Made Electrodes...

Inner ear malformations (IEMs) present significant challenges for cochlear implantation (CI), particularly the common cavity deformity, in which the cochlea and vestibule merge into a single space. Surgical and audiological outcomes in such cases depend on accurate electrode placement, nerve integrity, and tailored surgical strategies. We report the case of a pediatric patient with bilateral common cavity deformities who underwent sequential bilateral CI using the double posterior transmastoid labyrinthotomy (TML) approach with custom-made electrodes. The patient, diagnosed with profound bilateral sensorineural hearing loss at 1 year of age, showed bilateral common cavities with identifiable but reduced caliber seventh and eighth cranial nerves on radiological imaging and absent responses on auditory brainstem response testing. Based on preoperative imaging, a custom-made MED-EL FORM19 electrode (Innsbruck, Austria) was selected and adapted to match the patient's anatomy, aiming to optimize placement and reduce intraoperative complications. A staged implantation was performed. Surgery was uneventful, with intraoperative neural response telemetry confirming responses in both ears. At four-year follow-up, aided thresholds were stable in the speech frequency range (right ear: 40-60 dB HL; left ear: 50-65 dB HL). Speech audiometry in quiet demonstrated good detection and recognition, and language development was appropriate for hearing age, with significant improvement from baseline. This case illustrates that double posterior TML with custom-made electrodes is a safe and effective strategy for CI in complex IEMs such as common cavity deformities. The technique offers precise electrode placement, minimizes risks to the facial nerve, and ensures stable fixation. Early bilateral stimulation, active family involvement, multidisciplinary care in specialized centers, and tailored electrode design are critical to achieving favorable long-term outcomes. Multicenter studies are needed to further validate these findings and refine patient selection.