Cochlear Implant

It is an electronic device that allows patients with severe to profound sensory neural hearing loss to hear. With the ability to hear, these patients are able to communicate better and can lead a normal life.

A cochlear implant works by stimulating the auditory nerve endings, called spiral ganglia. By doing so, it bypasses the defective cochlea allowing the patient to hear.


Components of a Cochlear Implant

A cochlear implant consists of two components:

Sound is picked up by the microphone. This sound is processed by the processor. The processor analyses the sounds and converts them into electric signals.

The electrical signals are then sent to the transmitting coil. This in turn sends the signal to the implanted receiver via radio frequency. The receiver then decodes the signal and transmits it to the electrode array The electrode array then stimulates the spiral ganglion and auditory nerve. Once the auditory nerve is stimulated, it sends these electrical signals to the brain which finally interprets it as sound.


Candidacy for Cochlear Implantation

Both children and adults can be implantees. However, there are a few criteria that define a patient’s candidacy for cochlear implantations:

Candidates could be segregated into two categories, i.e. pre-lingual or post-lingual. This depends on whether they were deaf at birth or lost their sense of hearing at a later stage after learning to talk and communicate.

In the case of pre-lingual hearing loss, early intervention is very important for auditory stimulus. The lack of this auditory stimulus in the early developmental phase of a child causes a degeneration of the central auditory pathways. This will in turn limit the benefit in terms of speech and language development after cochlear implantation.

It is important to note that in cases of moderate to severe hearing loss, hearing aids would suffice and there is no need to go in for cochlear implantation. Only in cases of severe to profound hearing loss, would this be suggested.


Clinical Evaluation for Cochlear Implantation

A thorough evaluation of the patient is crucial in the selection process of candidates for cochlear implantation. The main aim is to determine the fitness and audiological suitability for implantation. It helps the surgeon to counsel the family about the expected outcomes of the surgery.

A medical evaluation by the way of a detailed history as well as a physical examination is important to confirm a patients fitness for general anaesthesia. The surgeon would also advise a CT Scan and MRI to be done. This is so that they are able to see the internal structure and identify any abnormalities that may complicate the surgery.

Audiological evaluations would include a Pure Tone Audiogram (PTA), Tympanometry (impedance audiometry), Otoacoustic Emissions (OAE), Brainstem Evoked Response Audiometry (BERA) and an Auditory Steady-state Response (ASSR).

It is compulsory for cochlear implantation patients to go through a hearing aid trial and evaluation to determine their candidacy. These tests include aided speech perception, aided free-field sound detection thresholds, as well as and discrimination scores.

A speech and language evaluation is required initially to assess the child’s communicative status as well as to determine any developmental language or articulation disorders. This would help to form a baseline for future evaluations post-implantation and assess the progress of the patient. Overall, this would help to adjust the programming of the patient’s device during habilitation.

At times, a psychological evaluation is advised when there may be concerns regarding the mental function or cognitive status of the patient. This is also an important step in identifying children who may have disabilities other than just hearing loss. This evaluation helps to further counsel parents and families about expectations after cochlear implantation.

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