Inner Ear Malformations with Transitional Forms between Cochlear Hypoplasia and Common Cavity: Embryological Insights, Imaging Characteristics, and Cochlear Implantation Strategies.

Objectives: To investigate the imaging characteristics, surgical approaches, and outcomes of cochlear implantation (CI) in patients with special inner ear malformations (IEMs) that show transitional forms between cochlear hypoplasia (CH) and common cavity (CC). Methods: Twelve children (eight males, four females), aged 10 to 43 months, with special IEMs were enrolled, and their inner ear structures were analyzed using detailed segmentation. Two surgical approaches were employed: the transmastoid slot labyrinthotomy approach (TSLA) for cases requiring customized electrodes, and the round window or cochleostomy approach for the remaining cases. Outcomes were evaluated using Categories of Auditory Performance (CAP), Speech Intelligibility Rating (SIR), and Meaningful Auditory Integration Scale (MAIS/IT-MAIS) at 12 months post-implantation. Results: Two main types of malformed cochleae were identified: common cavity-like and primitive CH types. All patients exhibited cochlear nerve deficiency and significant bilateral differences in their inner ear structures. Four patients underwent TSLA with customized electrodes, while the remaining patients received lateral wall electrodes via the round window or cochleostomy approach. Most patients showed improvement in auditory and speech capabilities following implantation. Conclusion: Inner ear malformations with transitional forms between CH and CC present unique challenges, requiring detailed preoperative evaluation and customized surgical plans. Even in severe cases, carefully planned surgery can lead to meaningful auditory rehabilitation.