Thursday, June 4, 2020

Auditory Brainstem Implant - Your Child a Candidate for Surgery?

An auditory brainstem implant is a device which helps people suffering from congenital hearing loss to start hearing sounds. It has been in use for more than 20 years, but still unknown for many people. This device functions like an artificial ear and hence is useful for kids with no ear development at birth.  
There are 3 varieties of auditory devices for the deaf children. They are
1.    Hearing Aid
2.    Cochlear Implant
3.    Auditory Brainstem Implant (ABI)
Auditory brainstem implant bypasses external,middle and internal ear and directly transmits signals to the brainstem.
In simple words hearing Aid is prescribed for patients suffering from external ear problems. It makes somebody to hear better by simply amplifying the sound impulses the device receives. Otherwise the hearing pathway works fine.
Cochlear implant is for someone who doesn’t have cochlea or the inner ear. Cochlea is a complex structure which converts the sound impulses into electric signals and it is carried from cochlea to the brain via the 8th cranial nerve. Cochlear implant is placed in the inner ear by an open surgical procedure.
Auditory Brainstem Implant or ABI is the most advanced brain implant which helps the person to hear even if he doesn’t have an Ear including the inner ear and auditory nerve.

WHAT?? Can you hear Without an Ear??

YES, Surgeon’s can make you hear even if you do not have an ear or hearing nerve in the brain.
How do they do that?
The electrode of the implant is inserted into the floor of the brainstem through a complex neurosurgical procedure. This electrode channel bypasses the auditory pathway till the brainstem nuclei.
 This device has to components.
1.    External receiver and processing unit
2.    Internal Electrode unit

ABI consists of an external and internal units. External unit is outside the skull and internal one is inside. Internal unit has a 12 electrode unit also.
ABI IMPLANT
External receiving unit has a sound receiving unit which looks like something like a hearing aid. The sound signals received by this go to the processing unit where it is converted as electric signals and it is transmitted into the internal unit. The internal electrode array consists of 12 electrodes arranged in 3 rows . These signals are carried over till the cochlear nuclei in the brainstem. From there the natural hearing pathway works as in normal persons.
This electrode array consists of 12 electrodes which will be in contact with the cochlear nuclei in the brainstem.
12 Electrodes arranged in 3 horizontal rows

Who can undergo ABI surgery?

ABI was first developed for patients with neurofibromatosis type 2 which is a genetic disorder. In this patients develop non cancerous tumours in both the auditory nerve which is the 8th cranial nerve. As a result patients will develop hearing loss on both sides and will ultimately become completely deaf.
Is Your child a candidate for ABI?
Recently the indications for ABI has been expanded. This is a good news for many parents having children with congenital hearing loss.
The recent indications are
·     Auditory nerve aplasia – congenital absence of auditory nerve
·     Auditory nerve hypoplasia – congenital underdevelopment of the auditory nerve
·     Non-NF2 tumour – eg. Non NF2 unilateral acoustic neuroma
·     Severe cochlear ossification
·     Head trauma

When to undergo the ABI surgery?

The recent guidelines gives an option of auditory implant placement even in very young children. Surgeon’s advice ABI in children more than 12 months of age. The recent reports says that the outcome is better when they are operated at a very young age, may be with in 12-24 months. Although it is a complex surgical procedure, it is comparatively safe for even young children. The only problem in these children are they may have other congenital defects like septal defects in the heart, tetralogy of Fallot etc. In such cases proper precautions has to be taken at the time of surgery.

Auditory Brainstem Implant surgery Outcome in Children?

The outcome analysis shows that children who are operated early in life shows better hearing results. Also an insufficient hearing function as in auditory nerve hypoplasia has a better outcome than in absent nerve. This could be due to a better development of the auditory pathway in the first group. ABI placement helps in improving the quality of life and better cognitive status. Many children are able to start their mainstream education years after the surgery.

Is surgery the end of treatment?

No, Long term rehabilitation is needed following the surgery. This may be a prolonged therapy in patients who don’t have previous hearing experience as in congenital hearing loss. Their brain has to be trained with the new set of auditory signals which are unknown to the brain till then. Brain has a special feature called “neuroplasticity”, where functions are taken over by a new set of neurons. This is better in young children and hence the outcome is also better in them.

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