Brain stem implant

A brainstem implant (English Auditory Brainstem Implant, ABI , also central auditory implant ) is a small electronic device for direct stimulation of the auditory pathway in the brainstem .

technology

A brain stem implant is a modified cochlear implant (CI); Instead of the inner ear , however, the first auditory nucleus ( nucleus cochlearis ) in the brain stem is electrically stimulated.

In addition to the stimulation electrode with a total of 21 individual button electrodes, the implant consists of an electronic part and a receiving antenna with a magnet, which are embedded under the skin in the skull behind the ear area (like a cochlear implant).

The receiving antenna of the implant receives signals from an external speech processor, which in turn picks up sound waves with a microphone. They are converted in the processor into a series of electrical impulses that are sent through the skin to the implant. The speech processor also contains the battery for power supply.

indication

The ABI has been designed and developed primarily for adult NF2 patients ( neurofibromatosis type 2 ). Among other things, NF2 means that tumors can develop primarily on the auditory nerve, which conducts acoustic signals from the cochlea to the brain. One consequence of this is that the tumor presses against the auditory nerves, but it can also damage other nerves in the same region. Therefore, there is usually no other option than to remove the tumor - the auditory nerves are often severed or damaged in such a way that acoustic signals can no longer be transmitted. This means that there is no longer any connection between the cochlea and the brain, so that no CI can be used.

For some years now, the range of indications has been expanded to include patients who are not affected by NF2, but who have, for example, a postmeningitically completely ossified cochlea, otosclerosis , auditory nerve aplasia or a post-traumatic auditory nerve injury or who are among "cochlear implant failures".

The ABI, developed by the company Cochlear AG, is approved in the USA by the Food and Drug Administration (FDA) for adolescents aged twelve and over. The device developed by MED-EL is only approved in the USA from the age of 15.

Contraindications

Contraindications for the implantation of an ABI are central deafness with functional disorders in the area of ​​the central auditory tract, severe general illness or a poor prognosis due to an underlying disease.

There are concerns among children under the age of twelve, as their body growth should have a negative impact on the implant and brain stem.

implantation

Depending on the individual case, tumors may be removed before the operation and the functional system subsequently checked using appropriate diagnostics. If there is no loss of function, an implantation takes place, in which a neurosurgeon places the electrode on the brain stem. He or she uses electrophysiological monitoring to find out about the functionally correct position.

The monitoring is intended to ensure that as many electrodes as possible later generate auditory impressions without any side effects. Side effects include dizziness, muscle twitching in the face or other parts of the body, swallowing or tingling in the throat; they occur when an electrode does not stimulate an auditory cell but a different sensory cell. Theoretically it is possible that changes in the area of ​​the brain stem cause electrodes only after some time to cause side effects. However, these are not to be expected spontaneously.

application

When the wound has healed, the first function test with stimulation of some electrodes is carried out after about 12 days. The patient experiences the first auditory impressions, which should also enable the recognition of linguistic information after a phase of practice. In comparison to a cochlear implant, however, speech recognition was described as worse: although environmental noises are perceived better and speech understanding is improved with simultaneous lip reading, speech understanding without lip reading is seldom achieved. However, this should also be improved for patients who have already been implanted through further technical development.

By 2003, 247 adult patients worldwide had been treated with an ABI. In Germany around 25 adults but no children under the age of 12 had been implanted by 2003. In June 2013, an operation was performed on a 3-year-old boy in the USA who was born without an auditory nerve due to a genetic defect.

Web links

• Cochlear implant care and central auditory implants - guidelines of the German Society for Ear, Nose and Throat Medicine, Head and Neck Surgery e. V., Bonn (PDF; 241 kB)

Individual evidence

1. ↑ Brain stem implant in non-tumor patients. Hannover Medical School
2. ↑ Interview with a neurosurgeon ( Memento of the original from August 17, 2004 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
3. ↑ Steffen Rosahl et al .: Brain stem implants for the restoration of hearing: Development and prospects. In: Dtsch Arztebl 2004; 101 (4): A-180 / B-155 / C-154 ( online )
4. ↑ [1]

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