Hearing: Cochlear and Auditory Brainstem Implants

Cochlear and auditory brainstem implants can improve sound and/or speech perception in the majority of patients with severe to profound sensorineural hearing loss. These bionic devices significantly improve quality of life by facilitating meaningful auditory interactions with the environment and in social situations, thereby enhancing oral communication skills. In this article, the authors discuss the mechanism of sound transduction used by these implants, device characteristics, indications for implantation, surgical techniques for device placement, complications and outcomes. Modern auditory implantable technologies can be implemented in a safe and effective manner, with exciting possibilities to improve hearing in diverse clinical situations and patient populations. Advances in the development of these auditory implants will allow us to more closely mirror the normal human experience of hearing in patients with peripheral and auditory pathology in the future. Key Concepts: Cochlear implants and auditory brainstem implants offer meaningful hearing in patients with severe deafness caused by inner ear pathology. Auditory implants work by converting an acoustic signal into an electrical one via an analogue to digital converter and speech processor, relaying those signals wirelessly to an implanted receiver-stimulator and activating an electrode array that is placed into the largest chamber of the cochlea called the scala tympani (cochlear implant) or on the surface of the cochlear nucleus (auditory brainstem implant). New sound processing strategies, such as continuous interleaved sampling, have dramatically improved the performance of implantable devices. MED-EL Corporation, Cochlear Corporation (Cochlear Americas) and Advanced Bionics LLC (Phonak) offer US Food and Drug Administration (FDA)-approved implants with varying electrode array options and speech processing technology. Device choice is often based on patient preference as all three are associated with good audiologic outcomes. Preoperative screening and assessment with a clinical history and exam, radiographic imaging and electrophysiologic testing are essential for evaluating a patient's candidacy for an implant and to assist in surgical planning. Most complications following cochlear or auditory brainstem implantation are minor, and in the hands of an experienced otologist or neurotologist, complication rates are low. Outcomes are variable among similar groups of cochlear implant users. A shorter duration of deafness and normal inner ear anatomy typically correlates with a better prognosis for open set speech perception (understanding spoken words without lipreading) in both paediatric and adult recipients. Outcomes are generally modest among auditory brainstem implant users, with most achieving sound awareness that enhancing lipreading. Paediatric and adult auditory brainstem implant users who do not have neurofibromatosis type 2 (NF2) as the cause of deafness have better audiologic outcomes than those with NF2. These non-NF2 users are deaf from small or absent inner ears or auditory nerves, scarred inner ears from infection or otosclerosis or damaged auditory nerves from skull fracture. Keywords: cochlear implant; auditory brainstem implant; sensorineural hearing loss; deafness; neurofibromatosis type 2