Auditory brainstem implants (ABIs)
Auditory brainstem implants (ABIs) may be suitable for children who are profoundly deaf (as hearing aids will not be an option for this type of deafness) and who are not suitable candidates for cochlear implants.
They stimulate the auditory brainstem directly, bypassing the ear and auditory nerve, to provide a sensation of hearing.
ABIs are still a fairly new development. They are mainly used by adults, but a small number of congenitally (born) deaf children who have an absent cochlea or cochlea nerve, and who are unable to benefit from a cochlear implant, may be referred for an ABI.
Most ABIs have been implanted in Europe, with just over 30 children who have had the procedure 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 cochlear nucleus of 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.
Hearing 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.
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.
Referral
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.
More information
ABI centres in the UK
- Guy's and St Thomas' (London)
- Emmeline Centre for Hearing Implants (Cambridge University Hospitals)
- Manchester Royal Infirmary
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:
- 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.
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