An Auditory Brainstem Implant (or ABI) is a device which restores some level of hearing to individuals who do not have a functioning auditory nerve. This type of hearing loss is relatively rare and is generally due to a malformation of the inner ear at birth or a condition known as Neurofibromatosis Type 2 (or Nf2 for short). Nf2 results in auditory nerve tumours and the surgical removal of these tumours can cause damage to the auditory nerve. The ABI is currently approved for use in adolescent and adult patients with Nf2 who have had their auditory nerve surgically damaged, although some experimental trials have begun exploring the possibility of using it for children born without an acoustic nerve.
Like a cochlear implant, the ABI consists of two components: an external speech processor and an internal implant that must be surgically placed in the brainstem. The speech processor for the ABI looks very much like those used for a cochlear implant. The internal component; however, is slightly different. In a cochlear implant, the electrode array is placed inside the cochlea. In an ABI, the electrode array is placed in a region of the brainstem called the cochlear nucleus. The electrode array then bypasses the cochlea and auditory nerve and stimulates the cochlear nucleus directly allowing a signal to reach the brain and be interpreted as sound.
Possible benefits of the ABI include:
- Awareness of environmental sounds
- Improvement in the ability to lipread conversation
- Ability to follow the rhythm and intonation of speech
Limitations of the ABI are as follows:
- Many noises sound the same at first and it may be difficult to identify sounds through the ABI
- It is usually not possible to understand speech without lipreading using an ABI
- Some patients are unable to hear anything after the ABI
To date, the Manchester ABI Programme has implanted over 60 patients with an ABI and there are approximately five people implanted per year. Apart from providing implants, several research projects are currently underway into this exciting new field at the programme.