A cochlear implant is a small electronic device that helps people hear. It can be used for people who are deaf or very hard of hearing. A cochlear implant is not the same thing as a hearing aid. The device is surgically implanted and works in a different way.
There are many different types of cochlear implants. However, they made up of several similar parts. One part is implanted into the bone around the ear (temporal bone) using surgery. It is made up of a receiver-stimulator. This part of the device accepts, decodes, and then sends an electrical signal to the brain.
The second part of the cochlear implant is outside the ear. It is made up of a microphone/receiver, a speech processor, and an antenna. This part of the device receives the sound, changes the sound into an electrical signal, and sends it to the inside part of the implant.
WHO USES A COCHLEAR IMPLANT?
Cochlear implants allow deaf people to receive and process sounds and speech. To some degree, these devices allow deaf people to "hear." It is important to note that these devices do not restore normal hearing. They are tools that allow sound and speech to be processed and sent to the brain.
Both children and adults can be candidates for cochlear implants. They may have been born deaf or became deaf after learning to speak. Children as young as 1 year old are now candidates for this surgery. The basis for selection may vary slightly from adults to children. The basic guidelines are:
The person should be completely or almost completely deaf in both ears, and get very little help from hearing aids. Anyone who can hear well enough with hearing aids is not a good candidate for cochlear implants.
The patient needs to be highly motivated. After the cochlear implant is placed, the person must learn how to use the device.
The patient needs to know what kind of hearing improvement should be expected after surgery. The device does not restore or create "normal" hearing.
Children need to be enrolled in programs that help them learn how to process sound.
Before being considered for the implant, the patient must have an exam by an ear, nose, and throat (ENT) doctor (otolaryngologist). Patients will also need specific types of hearing tests that are done with their hearing aids on. This may include a CT scan or MRI scan of the brain and the middle and inner ear.
Patients (especially children) may need psychological evaluation to determine if they are good candidates.
HOW IT WORKS
In a normal ear, sounds are transmitted through the air, causing the eardrum and then the middle ear bones to vibrate. This sends a wave of vibrations into the inner ear (cochlea). These waves are then converted by the cochlea into electrical signals, which are sent along the auditory nerve to the brain.
A deaf person does not have a functioning inner ear. A cochlear implant attempts to replace the function of the inner ear by turning sound into electrical energy. This energy can then be used to stimulate the cochlear nerve (the nerve for hearing), sending "sound" signals to the brain.
Most cochlear implants have similar parts.
Sound is picked up by a microphone worn near the ear. This sound is sent to a speech processor usually connected to the microphone and worn behind the ear.
The sound is analyzed and converted into electrical signals, which are sent to a surgically implanted receiver behind the ear.
The receiver sends the signal through a wire into the inner ear. From there, the electrical impulses are sent to the brain.
HOW IT IS IMPLANTED
During the surgery:
You will be asleep and pain free during this surgery.
A surgical cut is made behind the ear. You may need some of your hair shaved behind your ear. A microscope and bone drill are used to open the bone behind the ear (mastoid bone) to allow the inside part of the implant to be inserted.
The electrode array is passed into the inner ear (cochlea).
The receiver is placed into a pocket created behind the ear. The pocket helps keep it in place, and makes sure it is close enough to the skin to allow electrical information to be sent from the device. A “well” may be drilled into the bone behind the ear so the implant is less likely to move under the skin.
There will be stitches behind the ear.
You may be able to feel the receiver as a bump behind the ear.
Any shaved hair should grow back.
The outside part of the device will be placed 1 to 4 weeks after surgery to give the opening time to heal.
RISKS OF SURGERY
Most of the time, a cochlear implant is a safe surgery. However, all surgeries pose some risks. Common risks include:
Wound healing problems
Skin breakdown over the implanted device
Infection near implant site
These are problems are rare now that the surgery can be done through only a small cut.
Less common complications include:
Damage to the nerve that moves the face on the side of the operation
Leakage of the fluid around the brain (cerebrospinal fluid)
Infection of the fluid around the brain (meningitis)
Temporary dizziness (vertigo)
Failure of the device to work
RECOVERY AFTER SURGERY
Following your operation:
You may be admitted to the hospital to be watched overnight. (Many hospitals now let patients go home the day of surgery.)
Your health care provider will give you pain medicines. You may also get antibiotics to prevent infection.
Many surgeons place a large dressing over the operated ear. The dressing is removed the day after surgery.
A week or more after surgery, the outside part of the cochlear implant is secured to the receiver-stimulator that was implanted behind the ear. It is only at this point that you will be able to use the device.
The implant will be attached to the outside processor when the surgery is healed. You will begin to work with specialists to learn to "hear" and process sound using the cochlear implant. These specialists may include:
Ear, nose, and throat doctors (otolaryngologists)
Working with the specialists after surgery is a key part of the process. You will need to make a joint effort with your health care team to get the most benefit from the implant.
Results with cochlear implants vary widely. How well you do depends on:
The condition of the hearing nerve before surgery
Your mental abilities
The device being used
The length of time you were deaf
Some patients can learn to communicate on the telephone. Others can only recognize sound. Getting the most results can take up to several years. You need to be motivated. Patients are often enrolled in hearing and speech rehabilitation programs.
LIVING WITH AN IMPLANT
Once you have healed, you may need to make some changes. Most activities are OK. However, some health care providers recommend avoiding full-contact sports. This is to lessen the chance of trauma to the implanted device.
Most patients with cochlear implants cannot get MRI scans, because the implant is made of metal.
Balkany TJ, Brown KD, Gantz BJ. Cochlear implantation: Medical and surgical considerations. In: Flint PW, Haughey BH, Lund LJ, et al, eds. Cummings Otolaryngology: Head & Neck Surgery. 5th ed. Philadelphia, PA: Mosby Elsevier; 2010:chap 159.
Brown KD, Balkany TJ. Benefits of bilateral cochlear implantation: a review. Curr Opin Otolaryngol Head Neck Surg. 2007;15:315-318.
Papsin BC, Gordon KA. Cochlear implants for children with severe-to-profound hearing loss. N Engl J Med. 2007;357:2380-2387.
Sparreboom M, van Schoonhoven J, van Zanten BG, et al. The effectiveness of bilateral cochlear implants for severe-to-profound deafness in children: a systematic review. Otol Neurotol. 2010 Sep;31(7):1062-71.
Ashutosh Kacker, MD, BS, Associate Professor of Otolaryngology, Weill Cornell Medical College, and Associate Attending Otolaryngologist, New York-Presbyterian Hospital, New York, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.