Modern approaches to cochlear implantation in inner ear anomalies: audiological aspects

Indications for cochlear implantation are constantly expanding, going beyond severe and complete hearing loss, including patients with unilateral deafness and, recently, with congenital inner ear malformations (Karamert et al., 2022). Among congenital cases of sensorineural hearing loss, inner ear malformations (IEM) account for approximately 20% of cases, with up to 35% of them meeting the criteria for cochlear implantation (Sennaroglu et al., 2017). Due to the wider use of magnetic resonance imaging (MRI) and computerized tomography (CT) scanning of the temporal bone, the population of cochlear implant (CI) recipients among patients with IEM is also expanding, which naturally requires a retrospective assessment of clinical outcomes. At the same time, it is certainly important to evaluate not only the surgical results, which characterize, first of all, the safety of CI in this subgroup of patients, but also audiological outcomes: the degree of restoration of speech and auditory perception, without which it is impossible to get a complete picture of the effectiveness of cochlear implantation. Given the diverse anatomy of the cochlea in IEM, when planning cochlear implantation, determining of the electrode subtype, length and depth of its insertion, as well as the choice between CI or auditory brainstem implantation is of paramount importance not only for the success of the surgical intervention itself, but also for the results of subsequent auditory and speech rehabilitation. The purpose of this review is to analyze actual data about the audiological results assessment of cochlear implantation in patients with congenital IEM compared to patients with normal cochlear anatomy. We tried to identify IEM, in which CI gives the best results, as well as those malformations that require careful planning of surgery, specific selection of the electrode, as well as prevention of possible perioperative complications.