Hearing: Cochlear and Auditory Brainstem Implants

Abstract

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

Figure 1.

Cochlear implants consists of an external microphone, speech processor and transmission coil with an internal receiver‐stimulator connected to an electrode array which is placed in the scala tympany of the cochlea. Images courtesy of the Cochlear Corporation, Englewood, CO, USA. © Cochlear Americas.

Figure 2.

Facial recess approach for cochleostomy and electrode insertion. (a) A skin flap incision is made posterior to the auricle, the soft tissue and periosteum overlying the mastoid is elevated, exposing the bone for drilling of the facial recess. (b) After an intact canal wall mastoidectomy is performed, the facial recess is opened with care taken to avoid damaging the chorda tympany, facial nerve or ossicles. (c) A cochleostomy is created by drilling anteriorly (arrow) from the round window into the basal turn of the cochlea, and the electrode is inserted. A=antrum, C=chorda tympani, F=facial nerve, HSC=horizontal semicircular canal, I=incus, R=round window, S=stapes. Reprinted with permission from Witte RJ, Lane JI, Driscoll CL et al. (2003) Pediatric and adult cochlear implantation. Radiographics23: 1185–1200. © Radiological Society of North America.

Figure 3.

The Nucleus ABI24 system includes (a) the externally‐worn device, including a behind‐the‐ear microphone, speech processor and transmitter coil, and (b) the internal receiver‐stimulator, electrode array and ground electrode. The array consists of 21 active platinum electrodes on a Dacron mesh backing as shown in (c). Images courtesy of the Cochlear Corporation, Englewood, CO, USA. © Cochlear Americas.

Figure 4.

Endoscopic view of the typical approach to the DCN via the foramen of Luschka. VIIth nerve, IXth nerve, LCN: lower cranial nerves, LR, lateral recess; CP, choroid plexus. Reprinted from Vincent C (2012) Auditory brainstem implants: how do they work? The Anatomical Record295: 1981–1986.

Figure 5.

Cross section of the brainstem at the medullary‐pontine junction, demonstrating the major anatomical landmarks used during ABI placement. Abbrevistions: ICP, inferior cerebellar peduncle; t, taenia; VCN, ventral cochlear nucleus; DCN, dorsal cochlear nucleus. Reprinted from Vincent C (2012) Auditory brainstem implants: how do they work? The Anatomical Record295: 1981–1986.

Figure 6.

Schematic of processing and stimulation with an ABI. A three‐dimensional illustration of the human pontomedullary junction demonstrates positioning of the ABI electrode array in the cochlear nucleus (bottom). Reprinted from Vincent C (2012) Auditory brainstem implants: how do they work? The Anatomical Record295: 1981–1986.

Figure 7.

Representative EABR waveforms elicited from an ABI user during electrode positioning. Reprinted from Sanna M, Khrais T, Guida M and Falcioni M (2006) Auditory brainstem implant in a child with a severely ossified cochlea. Laryngoscope116: 1700–1703.

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Further Reading

Clark G (2003) Cochlear Implants: Fundamentals and Applications. New York: Springer.

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Lin HW, Herrmann BS and Lee DJ (2012) Cochlear implants and other implantable hearing devices. In: Ruckenstein MJ (ed.) Auditory Brainstem Implants, pp. 317–348. Cochlear Implants, pp. 126–132. San Diego: Plural Publishing.

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Zeng FG, Popper AN and Fay RR (2004) Cochlear Implants: Auditory Prostheses and Electric Hearing. New York: Springer.

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Puram, Sidharth V, and Lee, Daniel J(Jun 2014) Hearing: Cochlear and Auditory Brainstem Implants. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020287.pub2]