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 because it is surgically implanted and works in a different way.

There are many different types of cochlear implants. However, they are usually made up of several similar parts. One part of the device is surgically implanted into the bone surrounding the ear (temporal bone). It is made up of a receiver-stimulator, which accepts, decodes, and then sends an electrical signal to the brain.

The second part of the cochlear implant is an outside device. This is made up of a microphone/receiver, a speech processor, and an antenna. This part of the implant receives the sound, converts the sound into an electrical signal, and sends it to the inside part of the cochlear implant.

WHO USES A COCHLEAR IMPLANT?

Cochlear implants allow deaf people to receive and process sounds and speech. To a certain degree, they are devices that allow deaf people to "hear." However, it is important to understand that these devices do not restore normal hearing. They are tools that allow sound and speech to be processed and sent to the brain.

The way candidates are selected for cochlear implants is changing over time as the technology changes, and our understanding of the brain's hearing (auditory) pathways improves.

Both children and adults can be candidates for cochlear implants. They may have been born deaf or become deaf after learning to speak. Children as young as 1 year old are now candidates for this surgery. Although criteria are slightly different for adults and children, they are based on similar guidelines:

1. The patient should be completely or almost completely deaf in both ears, and get almost no improvement with hearing aids. Anyone can hear well enough with hearing aids is not a good candidate for cochlear implants.
2. The patient needs to be highly motivated. After the cochlear implant is placed, they must learn how to properly use the device.
3. The patient needs to have reasonable expectations for what will occur after surgery. The device does not restore or create "normal" hearing.
4. Children need to be enrolled in programs that help them learn how to process sound.
5. In order to determine if a patient is a candidate for a cochlear implant, the patient must have a medical evaluation by an ear, nose, and throat doctor (otolaryngologist). This evaluation may include a CT scan or MRI scan of the brain and the middle and inner ear.
6. 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 operate using several similar parts. Sound is picked up by a microphone worn near the ear. This sound is sent to a speech processor worn on the body, usually on a belt. The sound is analyzed and converted into electrical signals, which are sent to a surgically implanted receiver behind the ear. This 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

Surgery for inserting a cochlear implant is performed while you are fully asleep. A surgical cut is made behind the ear, sometimes after shaving part of the hair behind the 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 "well" created behind the ear. The "well" 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.

After surgery, there will be stitches behind the ear. You may be able to feel the receiver in its "well" behind the ear. Any shaved hair should grow back. The outside part of the device will be placed about 3 - 4 weeks after surgery, to give the opening time to heal.

RISKS OF SURGERY

A cochlear implant is a relatively safe surgery. As with all surgeries, there are possible risks. One of the most common complications is wound-healing problems. This includes problems such as skin breakdown over the implanted device, infection where the surgical cut was made, and the device coming out.

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

After surgery, you will probably be admitted to the hospital overnight for observation. Your health care provider will give you pain medicines and sometimes antibiotics to help with healing. Many surgeons place a large dressing over the operated ear. The dressing is changed the day after surgery.

Several weeks 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.

Once the surgery site is well healed, and the implant is attached to the outside processor and antenna, you will begin to work with specialists to learn to "hear" and process sound using the cochlear implant. These specialists may include:

• Audiologists
• Speech therapists
• Ear, nose, and throat doctors (otolaryngologists)

This is a very important part of the process. To get the most benefit from the implant requires a coordinated effort between you and the team of specialists.

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
• The surgery

Some patients can learn to communicate on the telephone. Others can only recognize sound. Getting the maximum results can take several years, and you need to be motivated. Patients are often enrolled in hearing and speech rehabilitation programs.

LIVING WITH AN IMPLANT

Once you have achieved full hearing, there are few restrictions. Most activities are allowed. However, some health care providers recommend avoiding full-contact sports, 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, Gantz BJ. Medical and surgical considerations in cochlear implantation. In: Cummings CW, Flint PW, Haughey BH, et al, eds. Otolaryngology: Head & Neck Surgery. 4th ed. Philadelphia, Pa; Mosby Elsevier; 2005: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.