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Hearing implants

Photo: There are four different types of hearing implant

There are four main types of hearing implants. The most common are cochlear implants and bone conduction hearing implants

There are also two less common types: middle-ear implants (MEI) and auditory brainstem implants (ABI).

Middle ear implants

Middle ear implants are used where conventional hearing aids or bone conduction hearing devices are not an option due to medical reasons.

The devices are surgically implanted hearing aids. They send a signal to the middle ear which mechanically vibrates the middle ear bones. This increases the sound vibrations entering the cochlea where the vibrations are converted into electrical signals sent to the brain.
They can be an option for children (five years and above) who have conductive, sensorineural or mixed hearing loss and are unable to use conventional hearing aids.

These implants are quite a new technology and only a small number children in the UK have them.

How do middle ear implants work?

There are different types of middle ear implant but they all work in similar ways. The implant is surgically inserted into the middle ear and the transducer is either attached to one of the middle-ear bones (ossicles) or to the round window between the middle ear and the cochlea (inner ear).

Middle ear implants have a microphone that picks up sound and a sound processor which converts the acoustic signals received by the microphone into electrical signals. The electrical signals are then processed and amplified to take into account the wearer's type and level of deafness.

The electrical signals are converted into a mechanical vibration that is delivered directly to the middle ear, this enhances the transmission of sound waves to the inner ear (cochlea). In the cochlea, the sound waves are detected by hair cells and perceived as sound.

Middle ear implants can be:

  • fully implantable – all parts of the device under the skin, meaning there is no need for an external audio sound processor, or
  • semi-implantable – part of the device is worn on the ear externally and part placed in the middle ear allowing the ear canal to remain open.

What are the different types of middle ear implant?

Fully implantable middle ear implants (Cochlear Carina, Envoy Esteem)

This type of device is implanted completely under the skin with no external parts. The microphone of the Cochlear Carina is implanted under the skin behind the pinna of the ear (outer part) whereas the Envoy Esteem uses the movement of the eardrum as a microphone. A sound processor is implanted in the bone behind the ear which converts sound vibrations into electrical signals. The processor then amplifies these signals which create intensified mechanical vibrations in the middle ear. The increased sound vibrations then enter the inner ear as they usually would and are converted into electrical signals which are sent to the brain.

Having a fully implantable device means there are no external parts to worry about. It can be worn all day and night as well as in the shower, when washing your hair or swimming.

Semi-implantable middle ear implants: (MED-EL Vibrant Soundbridge)

This type consists of an external audio processor which sits behind the ear and contains a magnet. The processor is held in place by magnetic attraction to the implant under the skin.

The sound processor of the Vibrant Soundbridge can also be made fully waterproof with a protective cover.

Your child’s audio processor should be upgraded every five years to keep up with any new technological advances.

Is a middle ear implant suitable for your child?

Your child may be considered for a middle ear implant if they have a medical reason which prevents them from being able to wear a conventional hearing aid or a bone conduction hearing device.

Middle ear implants are suitable for children who:

  • have previously had surgery on their ears which makes using a conventional hearing aid difficult (for example mastoid cavity problems following surgery for cholesteatoma).
  • were born with underdeveloped outer ears (microtia, atresia)
  • aren’t able to wear their bone conduction hearing aid due to medical problems of the soft tissues or loss of fixture
  • aren’t able to wear conventional earmoulds due to allergies, eczema or recurrent outer ear infections (otitis externa).

They are also suitable for children who can’t use conventional hearing aids and have:

  • stable (non-progressive) hearing loss
  • unilateral or bilateral (affecting both ears) deafness
  • moderate to severe deafness
  • hearing loss that can be conductive, sensorineural or mixed
  • no middle ear infections
  • stable bone conduction thresholds with less than 15dB deterioration in 2 years

Process for getting a middle ear implant

Your local audiology service should provide a full and comprehensive assessment of your child’s hearing and your child will normally be fitted with a conventional hearing aid for a minimum of four weeks.

A hearing aid may not be beneficial for your child or they might not be able to wear one due to a medical condition. If this is the case and your child meets the criteria set by implant manufacturers you should be given the option of being referred to the Hearing Implant Service for further assessment. 

The assessment process for a middle ear implant will be similar to the one for getting a bone conduction hearing device and your child may be seen by a number of different people from the multidisciplinary team.

Surgery

The operation is usually done under general anaesthetic and can take between one and two hours. The implant is then activated around six to eight weeks later. A follow-up appointment will be made after the initial activation to fine tune the processor with further appointments as required.

Technology

At present the Cochlear Carina middle ear implant isn’t compatible with any assistive listening devices, such as loop systems or radio aids.

The Medel Soundbridge middle ear implant does not have a telecoil, however, the audio processor is able to connect to the loop and other wireless devices via a streamer. A streamer sends signals digitally to your child’s hearing device and links with other products using Bluetooth such as mobile phones, laptops or tablets.

Find out about other products and technology that may help your child at home or school.

Find more information on funding and lost equipment as well as transferring care to another service and service standards.

Batteries

Middle ear implant batteries work in various different ways depending on the make and model. Check the supplier's websites to find out more about how long your child's battery should last, how to charge it and how to get hold of replacements.

Support groups

Contact support groups and other organisations, or read blogs written by people who use middle ear implants.

www.facebook.com/NDCS.UK
www.cochlear.com/uk/home/connect/support-organisations
www.medel.com/uk/user-support
blog.medel.com
www.facebook.com/medel.hearlife

Middle ear implant centres in the UK

Guy's & St Thomas' Hearing Implant Centre, London

University Hospitals Birmingham Hearing Implant Programme

University of Southampton Auditory Implant Service

Auditory brainstem implants (ABIs)

Auditory brainstem implants (ABIs) could be considered for deaf children who receive little or no benefit from hearing aids and aren’t suitable candidates for cochlear implants.

ABIs are still a very new development. Working in a similar way to a cochlear implant, an ABI stimulates the auditory brainstem directly, bypassing the ear and auditory nerve, to provide a sensation of hearing.

ABIs are mostly used by adults who have suffered trauma to their hearing nerve and would therefore not benefit from hearing aids or a cochlear implant, but a small number of congenitally (born) deaf children have an ABI.

Most of them have been implanted in Europe, with just a few having the procedure in the UK. We estimate there to be around 13 congenitally deaf children with an ABI living in the UK.

Why might an ABI help?

The inner ear or cochlea enables us to hear. As sound passes through the outer and middle ear, tiny hair cells in the cochlea vibrate, converting sound waves into electrical signals. These electrical signals travel along the hearing nerve (also known as the auditory nerve) to the brain.

Most sensorineural deafness is caused by loss of, or damage to, these hair cells. Where enough functioning hair cells remain, hearing aids may help by amplifying sounds to a level at which they can be heard.

In cases of severe to profound deafness, there may not be sufficient functioning hair cells for hearing aids to be effective. For these children a cochlear implant may help.

For a very small number of deaf children their deafness may be the result of an absent or malformed auditory nerve or cochlea. In these children sound can’t pass effectively between the inner ear and the brain, so hearing aids or cochlear implants may be of very limited or no benefit, and they may be considered for an ABI.

What is an ABI and how is it different from a cochlear implant?

Similar to a cochlear implant in the way it looks and works, an ABI has two parts. The external part consists of the microphone and speech processor (which either sits behind the ear or is body-worn), a lead and a transmitter coil, and a microphone.

Unlike a cochlear implant where the electrode is inserted into the cochlea, the internal part of the ABI is surgically implanted directly onto the brainstem, therefore bypassing the cochlea and auditory nerve. It includes the receiver and a number of electrodes that directly stimulate the brainstem, to provide a sensation of hearing.

A few weeks after the operation, the external parts are fitted and the implant is switched on. The speech processor is tuned over a period of time to meet the wearer’s needs. Following implantation, long-term support from professionals is crucial to encourage the wearer to learn to listen to and understand the new signals from their implant.

When are ABIs offered?

ABIs have been used for adults who have been diagnosed with Neurofibromatosis Type II (NF2) – a condition causing tumours to grow on the hearing nerves – or have suffered trauma to their hearing nerve meaning it’s no longer useful (for example, following surgery).

If the hearing nerve has been damaged in this way, hearing aids and cochlear implants are of no benefit because sounds can't transfer from the ear to the brain along the nerve.

Up until recently ABIs have only been offered to adults who have previously had hearing and use speech to communicate. The ABI provides a sensation of hearing that can help aid lip-reading and provide other clues used in spoken communication (for example rhythm and speed of speech). These adults are unable to use the ABI alone to understand speech without the additional help of lip-reading etc.

However, in the last few years ABIs have occasionally been given to congenitally deaf children, mostly in Europe but with a few in the UK.

In January 2005 UK guidance was published by the National Institute of Clinical Excellence (NICE) which recommended the ABI procedure only for adults and young people who have had surgery to their hearing nerve. NICE haven’t issued any guidance on using ABIs for deaf children.

The British Cochlear Implant Group (BCIG), clinicians and professionals working within the paediatric cochlear implant programmes are not endorsing routine use of ABIs in congenitally deaf children and we recognise and welcome the caution that is adopted around the fitting of children in the UK at this time. However, we acknowledge that there may be families who wish to explore this option for their child.

Following a request from the National Deaf Children’s Society to clarify funding of ABIs for children, NHS England published a policy, Clinical Commissioning Policy: Auditory brainstem implant with congenital abnormalities of the auditory nerves of cochleae.

How much could my child hear with an ABI?

Because of the small numbers implanted so far and the variability of results, it’s difficult to predict how well children generally may be able to use the information they receive from an ABI and whether it could help them develop spoken language.

Most are able to recognise and discriminate different environmental sounds such as a doorbell or phone ringing.

What is the assessment process?

Children who have no or a very small auditory nerve may show virtually no response to very loud sounds when wearing hearing aids and may be referred to a specialist cochlear implant team for an assessment. Medical assessment, including special x-rays or scans of the ear, is essential to determine the size and/or absence of the auditory nerve.

However, whilst extremely important, a child’s hearing levels are not the only consideration. The child’s communication abilities and general development must also be assessed by professionals, including speech and language therapists and Teachers of the Deaf.

How can I refer my child?

If your child has been using a hearing aid for sufficient time with little benefit, you should contact your ear, nose and throat (ENT) consultant or the audiology service that fitted the hearing aid to discuss your concerns.

If you feel your child should be assessed for cochlear or auditory brainstem implantation, you should contact your ENT consultant or audiologist.

If appropriate, your ENT consultant will refer you to a children’s cochlear implantation centre for specialist assessment.

ABI centres in the UK

ABI research

There is currently very limited published research worldwide on the procedure, use of and benefits of ABI in deaf children, but there are clinical trials ongoing in America.

Some published research is: