Cochlear Implants

When should a cochlear implant be fitted?

The simple answer is "as early as possible."

In babies who are diagnosed through screening programmes, this may mean the benefits of an implant are obtainable by five to six months of age. In young children who have never heard before, the brain gradually loses its ability to utilise sound. By the age of 4-5 years in a child with profound hearing loss, this ability has diminished so much that even a cochlear implant fitted after this stage, will be of limited benefit.

Children and adults who have a progressive hearing loss and who have already developed oral language may all potentially benefit from a cochlear implant.

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The duration of profound deafness has a significant impact on the potential benefit of a cochlear implant. In an adult or child,an ear which no longer is able to benefit from amplification of a hearing aid would be expected to slowly lose its nerve supply over 2 decades or so. Therefore, adults with a long duration of deafness and no hearing aid use would be expected not to be able to hear as well with an implant, compared to someeone who receives an implant after a shorter duration of deafness. Again, the message is, "as early as possible". We encourage adults with deteriorating abilities to hear on the telephone (with hearing aids on) to come for an assessment.

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How is the assessment for a cochlear implant done?

The assessment usually starts with referral from an audiologist or hearing therapist or advisor on deaf children to the public or the private cochlear implant programme. Assessment is performed by myself and cochlear implant specialist audiologists and hearing therapists. Information from those making the referral is utilised, in addition to further testing of the hearing, and MRI (magnetic resonance imaging) and sometimes CT (computerised tomography) scanning of the ears and head.

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Children (New Zealand Residents): The assessments are discussed as a group with the implant candidate (or parents),myself, the cochlear implant audiologist and the hearing therapist. A recommendation may then be made for public funding of the implant, to the Northern Cochlear Implant Trust. This decision is made by a committee of cochlear implant experts in surgery, audiology and hearing therapy, and would include those who are directly responsible for the hearing care of the candidate. In New Zealand, public funding is expected to cover most cochlear implant costs for life.At present there are long waiting lists for cochlear implantation for adults, despite recent imporvements in funding.

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Private funding of cochlear implants and cochlear implant surgery is also possible. In this situation, there is no requirement for a review by the funding committee, and the decision is made by yourself with advice and recommendations from your cochlear implant audiologist/habilitationist team at Hearing House and myself.

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Cochlear Implant surgery

I perform this surgery at Southern Cross Gillies Hospital, 160 Gillies Ave, Epsom. This is where all Cochlear Implant operations take place in Auckland (see the map on my website).This procedure involves the insertion of the receiver with electrode array. It is regarded as a fairly routine operation, typically taking about 2 1/2 hours in the operating room.  It is performed under general anaesthesia (asleep).A small amount of hair is shaved from behind the ear. An incision (cut) is made behind the ear and a pocket created to house the implant. Some air cells in the mastoid bone, which is part of the ear, are removed to enable access to the inner ear. The electrode array (with 22 electrodes along it) is inserted through the mastoid, over the top of the facial nerve and into the "round window" of the inner ear. The device is secured and the incision is then closed using buried dissolving stitches and skin glue. A head bandage is worn overnight. In some cases, it may be possible to return home at the end of the day, and for some, an overnight stay is required.We prescribe paracetamol and an anti inflammatory (such as brufen or celebrex) to manage discomfort for 5-7 days post operatively. Most children seem to have very little pain, and often "run around" normally the next day (depending on their age , of course!).

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What are the risks of a cochlear implant?

These include:

• Device failure. The internal device is guaranteed for 10 years. The failure rate in children is slightly greater than in adults, but less than 1% over this time. If this occurs, the implant can be removed and replaced.

• Infection: this could necessitate the removal (and replacement) of the device. Very uncommon-I have not had this occur in any of my patients.

• Facial nerve injury: because this nerve runs through the middle ear, it is at risk in a surgical procedure on the ear. In experienced hands, this risk is minimal. I have not had this occur in any of my patients. 

• Facial nerve stimulation: In some people who have had meningitis or who have lost hearing as a result of otosclerosis, it is possible that sound may result in facial twitching. It is usually possible to overcome this with programming of the device.

• Temporary or permanent alteration of the sensation of taste on the side of the tongue. This may occur uncommonly as a result of damage to the "chorda- tympani nerve" which runs also through the ear and the mastoid bone.

• Meningitis: this is a rare consequence of cochlear implantation, and also deafness itself presents a greater risk of meningitis. For this reason, all children and adults should be fully vaccinated against  the bacteria ,streptococcus pneumoniae. This is something which you should ask your GP to do. This vaccination is currently routine in babies in New Zealand.

• MRI Scanning- the current implants are compatible with MRI scanning- but if the head is being scanned, there is usually a zone of 10cm around the implant which is not visible. The removeable magnet in the implant may be removed temporarily, with a small procedure, to reduce this invisible zone.

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Cochlear Implant Programming

This is done post operatively, between days 1-7. The first appointment is called "switch on", where each individual electrode is adjusted to maximise the ability to hear. in the subsequent weeks and months, the stimulation of each electrode is adjusted. Usually, minimal adjustment is required after a year of use. Programming is performed for children at Hearing House in Auckland and at outreach clinics in Whagarei, Hamilton, Rotorua and Tauranga . For adults this is performed at Hearing House. Future programming is increasingly able to be done remotely.