There are also two less common types: middle-ear implants (MEI) and auditory brainstem implants (ABI).
Middle-ear implants are surgically implanted hearing aids which send a signal to the middle-ear which mechanically vibrates the middle-ear bones.
Middle-ear implants can be fully implantable (all parts of the device under the skin) or semi-implantable (part of the device worn on the ear).
How do middle-ear implants work?
There are different types of middle-ear implant but they work in similar ways. The middle-ear implant is surgically inserted into the middle ear and either attaches onto one of the middle-ear bones or to the round window between the middle ear and the cochlea.
Middle-ear implants have a microphone to pick up sound and a sound processor which converts the acoustic signals received by the microphone into electrical signals. The electrical signals are processed and amplified to take account of the wearer's type and level of deafness.
The electrical signals are then converted into a mechanical vibration that is delivered directly to the middle-ear enhancing 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.
Who is suitable for a middle-ear implant?
They are suitable for certain people who are unable to use conventional hearing aids and whose hearing loss is conductive, sensorineural or mixed, and:
- stable (non-progressive)
- bilateral (affecting both ears)
- moderate to severe.
Who can get a middle-ear implant?
Middle-ear implants are funded centrally by NHS England. There is similar central funding in Northern Ireland, Scotland and Wales.
They are only funded when alternative hearing aids or other implantable devices are medically unsuitable.
Middle-ear implants may be suitable for young people who:
- were born with underdeveloped outer ears (for example microtia or atresia)
- have had a bone conduction hearing implant (BCHI) but were unable to use it due to loss of abutment
- are unable to wear conventional earmoulds due to allergy, eczema or recurrent ear infections
- have had previous surgery on the ears making conventional hearing aid use difficult (for example mastoid cavity problems following surgery for cholesteatoma).
Middle-ear implant manufacturers
If you think your child may be a suitable candidate for a middle-ear implant and are interested in finding out more, ask your audiologist or ear, nose and throat (ENT) doctor to refer you to a specialist auditory implant centre.
MEI centres in the UK
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 11 (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
- Guy's and St Thomas' (London)
- Emmeline Centre for Hearing Implants (Cambridge University Hospitals)
- Manchester Royal Infirmary.
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:
- Auditory brainstem implant (ABI): new frontiers in adults and children
- Auditory brainstem implantation in 12 to 18-year-olds
- Hearing restoration with auditory brainstem implant in three children with cochlear nerve aplasia
- Complications in auditory brainstem implant surgery in adults and children
- The Subjective Outcome of Auditory Brainstem Implantation.