Cochlear Implantation

16 Cochlear Implantation


16.1 Principles


• A CI is a device implanted into the cochlea that directly stimulates nerve fibres within the auditory system, allowing the perception of sound (Fig. 16.1)


figure Stimulates cochlear n fibres (spiral ganglion cells) with acoustic sounds that have been processed into electrical energy


figure Primary aim is to provide user with greater speech recognition ability than is possible with conventional amplification


figure Microphone (worn like an HA) converts sound into electrical signals; speech processor analyzes and digitizes this information into coded signals (splitting into frequency bands); transmitter is held over receiver by a magnet and sends the code across the skin as radiofrequency waves; coded signal is converted to electrical signals that pass to the electrode to allow for stimulation of the nerve fibres (tonotopic arrangement)


figure Goal in children: to achieve age-appropriate speech, language, and listening skills; to reduce intervention over time; to have mainstream education; to be fully integrated into hearing world


figure Goal in adults: to support lip-reading; to improve communication ability and develop telephone and open-set speech; to reduce effort of communication; to be in touch with surroundings


16.2 Indications


• Paediatric: children with pre-lingual deafness have a critical period in which they can be usefully implanted (<2 years) for greatest benefit; those children (or adults) who lost hearing after language acquisition have established central auditory pathways so can be implanted up to 10 years after the onset of deafness:


figure Profound sensorineural hearing loss in both ears (e.g., unaided >90 dB across speech frequencies)


figure Lack of progress in the development of auditory skills


figure No medical contraindications


figure High motivation and appropriate expectations from family


figure Precise audiometric inclusion criteria vary from centre to centre and as experience in CI grows


figure Assess speech, language, and listening skills appropriate for age, developmental stage, and cognitive ability


• Adult >18 years:


figure Pre-linguistic or post-linguistic onset of severe-to-profound hearing loss


figure Audiometric criteria and exact test used to make assessment vary between centres


figure Consider when hearing worse than 90 dB HL at 2 and 4 Hz; adequate benefit from a conventional HA considered when >50% score on BKB (Bamford-Kowal-Bench) sentence testing at sound intensity of 70 dB SPL, so needs to be worse to justify CI


figure No medical contraindications


figure A desire to be part of the hearing world


16.3 Contraindications


• Audiometric:


figure Presence of significant residual hearing


• Medical:


figure Active infection (acute or chronic OM)


figure Ossified cochlea


figure Cochlea non-development


figure Unrealistic expectations


16.4 Surgery


• Procedure:


figure General anaesthesia, mastoidectomy with posterior tympanotomy


figure Cochleostomy anteroinferior to round window membrane


• Device:


figure Multi-channel electrodes generally used, with variable number of specific electrodes depending upon device used


figure Intra-operative testing with neural response telemetry, checks that implant is working and in contact with auditory n endings


figure Post-operative switch-on usually after ~4 to 6 weeks with continued “remapping” over next few years


• Risks of surgery:


figure Facial paresis/paralysis (temporary or permanent): 1:500 to 1:1000


figure Taste disturbance (temporary): 10%


figure Loss of residual hearing: dependent on surgical technique and implant used


figure Balance dysfunction/vertigo—temporary: most patients; long-term balance dysfunction rare


figure Infection: <1% but may/usually necessitate removal of implant


figure Meningitis—perioperative: 1:5000 (vaccinate vs. pneumoncoccus, Hib); long-term risk similar to general population


16.5 Expected Outcomes


• Does not provide normal hearing


• Gradual improvement in performance especially in first 6 months, but for up to 2 years


• 95% adults have improved lip-reading, 50% have acquired open-set speech discrimination, 35% can use telephone


• 90% children aided <2 years enter mainstream education


• Reliability: 97 to 99% functioning at 10 years


16.6 Special Considerations


• Which ear?


figure Better-hearing or worse-hearing ear, depending if plan for bimodal stimulation


figure HA use in implanted ear usually predictive of better performance than non-aided ear


figure Vestibular function


• Bimodal stimulation; HA one ear, CI in the other


figure Helps in background noise, for sound localization, and allows for better music appreciation


• Bilateral CIs


figure Improved sound localization, speech understanding in quiet and noise


figure Guaranteed to implant better ear


figure Improved speech, language, and auditory development in children


figure If one fails, not completely isolated


figure Simultaneous bilateral CI recommended in adults and children, especially when codisability (e.g., blindness)


• Hybrid implants, “electroacoustic stimulation”


figure Shorter electrodes used for high tone loss with conventional HA for lower frequencies



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Jul 4, 2016 | Posted by in OTOLARYNGOLOGY | Comments Off on Cochlear Implantation

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