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What is a cochlear implant and how does it work?
A cochlear implant is a surgically placed device that receives sound and transmits the resulting electrical signals to electrodes implanted in the cochlea of the ear. It consists of 2 main parts: the external and the internal components. The external part consists of the microphone, sound processor and transmitter system. It is held in place by a magnet that connects it to the internal part consisting of the implanted receiver and electrode system. The microphone picks up the sound which is analyzed and converted into digital code by the speech processor. This signal is sent to the headpiece, transmitted across the headpiece and then distributed to the electrode array inserted into the cochlea. These electrodes send electrical impulses to stimulate the auditory nerve. By doing so, the implant bypasses the damaged or non-functioning inner ear that causes the hearing loss. The entire process is rapid enough to not produce any noticeable delays.
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Candidacy
For individuals aged 18 years and above, moderate to profound sensorineural hearing loss, with less than or equal to 50% sentence recognition who receive little to no benefit from hearing aids can be considered. Consideration of CI in children requires a more multidisciplinary approach. Children aged 12 months and above with severe to profound hearing loss, showing no auditory development even after 3 to 6 months of hearing aid use can be referred for a cochlear implant. Older children who have not been identified early, or with long standing hearing loss with limited benefit from hearing aids can also be considered for cochlear implants, but realistic goals and expectations need to be discussed with parents prior to the surgery.
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Pre-implant evaluation
A pre surgical evaluation is necessary to determine the candidacy and is usually conducted by a multi-disciplinary team, including (but not limited to) ENT surgeon, nurse, audiologist, speech language pathologist and pediatrician. A thorough audiological evaluation determines the child’s level of hearing as well as benefit with hearing aids. A medical examination is required to rule out medical contraindications and to prevent possible surgical risks.
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Contraindications
Contraindications can include – ongoing chronic otitis media or mastoiditis, complete absence of the cochlea or the auditory nerve, very narrow internal auditory canal, severe developmental delays or intellectual disabilities where management of a surgically implantable device may be difficult.