Cochlear Implant is an electronic device which is surgically implanted in inner ear and is activated via a device worn outside. It is used to produce a sense of sound in a person who is deaf or hard of hearing.
A Cochlear implant directly stimulates auditory nerves and is used when all of the hearing aids fail.
The device is implanted surgically, and the patient has to undergo a thorough checkup before he/she can have a cochlear implant.
Cochlear implants are used to treat deafness caused due to malfunction or damage of cochlea which is a part of inner ear. Cochlea is a spiral-shaped structure that looks like a snail shell. Cochlea has thousands of hair-like structures called as stereocilia.
Stereocilia receive sound vibrations and convert them into electrical signals. These electrical signals are then received by auditory nerves which takes the message to the brain which interprets the sounds.
A cochlear implant consist of following parts:
- Microphone: It is an external part of the device. It picks up sound from the environment and sends them to the speech processor.
- Speech Processor: It receives sound from the microphone and turns it into a digital signal and transfer these signals to the transmitter.
- Transmitter: It transfers the signal to the receiver which is implanted under the skin.
- Receiver: It determines, how much electric current should pass to electrodes. The amount of current determines the loudness of sound.
- Electrodes: Electrode receives the signal from receiver and triggers the auditory nerves in cochlea which transfer the signal to brain where the sound is interpreted.
Indications for Cochlear Implant Surgery:
A cochlear implant can be implanted in both children and adults, but it is not an option for every individual with hearing loss. The criterion of selection is different for adults and children, but is based on similar guidelines:
- The person must be deaf or have profound hearing loss in both ears, and also using hearing aids are not giving desired results. If hearing aids are working for the individual, then he/she is not considered for cochlear implants.
- A person is considered a good candidate if he/she is born deaf or have become deaf after learning to speak and does not have any other medical condition that makes the surgery risky.
- The person should be highly motivated and must be passionate about becoming a part of the hearing world. After implantation, the patient has to learn how to use the device appropriately.
- The person should have realistic expectations post-implantation as the implant does not restore or cure the hearing loss.
- Children should be educated about how to process sound.
- Patients should be assessed by psychologists to decide if they are good candidate for an implant.
Process of Cochlear Implant surgery:
Before the surgery, an evaluation of the patient is done to assess if the patient is an appropriate candidate for the surgery or not.
Evaluation is done by a team which consists of the surgeon, cochlear implant audiologist, a radiologist and a psychologist as per need. This team gives a series of tests including a hearing test, CT scan, and other required tests.
- After the evaluation, if the patient is found to be a good candidate, the surgery is performed. The operation takes about 60-75 minutes and is carried out under general anesthesia. While preparing for this surgery, hair of the patient is shaved off to make access easier.
- Surgeon makes a cut behind the ear and drills through the mastoid bone ( part of the temporal bone of skull).
- Through this opening, electrodes of implant are inserted in cochlea.
- A pocket is created in the bone behind the ear in which the receiver is placed. Pocket helps to secure the place of the receiver.
- The incision is than closed with dissolvable stitches.
- After about one month of surgery, outside device, i.e. microphone, speech processor and transmitter are placed and adjusted outside ear.
- Your team will teach you how to take care of implant and how to listen through the implant. Some cases require more training and more time to fit.
- Initial testing of the implant is performed by an audiologist while the patient is in the operation theatre to confirm that the electrodes are functioning correctly.
- After surgery training and therapy is required to learn how to interpret this new electric signals.
- External part of implant must be removed before bathing and swimming.
- MRI for person with cochlear implant need a particular procedure to be performed before MRI.
- The person with an implant should stay away from sports. Any accident or sports may damage the device.
- The person will need to recharge the battery of implant or may need a new implant.
Complications of Cochlear implant surgery:
The cochlear implant surgery is relatively a safe one. However, all surgeries do have some risks and complications, but they are less frequent as the surgical procedure is done via a small cut, but may include following complications:
- Difficulty in healing of wound.
- Infection at the site of surgery, but to reduce this risk patient is given an injection of antibiotic during operation.
- There is a small risk of damaging facial nerve as it runs through the ear. If damaged, it can cause facial palsy, wherein the facial muscles of the affected side are weakened.
- Sometimes damage in facial nerve that carries taste sensation from the tongue to the brain results in taste disturbances. To minimise the chances of facial nerve damage, it’s monitored during the operation by placing tiny needles in the face.
- Skin lesions over the implanted device.
- Cerebrospinal fluid (CSF) may leak sometimes. It may resolve on its own or have to be drained, or packing is inserted in the ear under general anesthesia. Furthermore, the infection can spread to this fluid causing meningitis.
- Also, there is a rare possibility that the device may not work. You must inform the surgeon in that case, and they will take all the necessary steps to replace it, etc.