Cochlear Implants
Images Courtesy of Cochlear Americas
Cochlear implants are electronic devices that provide sound information to individuals with severe to profound hearing losses. A cochlear implant is a surgically implanted device for those with too much hearing loss to benefit from the use of hearing aids. The cochlear implant system consists of two parts: an internal portion and an external portion. The internal portion is surgically implanted under the skin, behind the ear. It consists of a receiver and an electrode array. The electrode array is inserted through the skull and middle ear into the cochlea (inner ear). The external portion of the system consist of a speech processor that is worn behind the ear and resembles a hearing aid, and a transmitting coil that attaches to the head by magnets near the speech processor. A cochlear implant bypasses the damaged parts of the auditory system and stimulates the auditory (hearing) nerve directly with electrical impulses.
How does it work?
The external speech processor contains microphones that pick up sounds. The processor then analyzes and converts these sounds into special codes. These codes are sent to the transmitting coil and through the skin to the implant. The internal implant receives these codes and coverts the signal to an electrical impulse. These electrical impulses are sent through the electrode array and stimulate the hearing nerves at specific locations. The auditory nerve picks up these signals and sends them to the brain where they are interpreted as sound.
How Hearing and CI Work - Courtesy of Cochlear Americas (Requires QuickTime)
Cochlear implants are different from hearing aids. Hearing aids simply amplify sounds. A person with severe to profound hearing loss is not able to process this louder sound normally because it is still going through the damaged part of the inner ear. A cochlear implant does not make sounds louder. It bypasses the damaged parts of the inner ear and sends electrical signals directly to the auditory nerve.
The cochlear implant and speech processor must be programmed by a trained audiologist. This is done several weeks after the surgery, and on an ongoing basis. During a programming session the electrodes are tested to make sure they are functioning properly and measurements are made as to how much electrical stimulation is needed on each electrode for the patient to perceive it as sound. Programs, called maps, are then developed, and multiple maps can be made for different types of listening situations. The amount of electrical stimulation that is required can change over time, requiring re-programming of the processor.
Who is a candidate?
Current FDA guidelines state that candidates must meet the follow general criteria:
- Adults (age 18+) with a moderate to profound bilateral sensorineural hearing loss, with poor speech understanding even with appropriately fit hearing aids
- Children (25 months to 17years 11 months) with severe to profound bilateral sensorineural hearing loss, with poor speech understanding, and a lack of progress in the development of auditory skills
- Infants (12 months to 24 months) with profound bilateral sensorineural hearing loss, and a lack of progress in the development of auditory skills
- All patients must be in good general health and have no medical contraindications
These guidelines are general, and there are exceptions, as well as more specific criteria to determine candidacy. To determine if you are a candidate please call to schedule an appointment.
Surgical Procedure:
The surgery is performed in the hospital under general anesthesia. The procedure takes approximately three hours. Patients are generally able to go home the same day as surgery (outpatient surgery), but do occasionally stay overnight.
The surgical approach used to place a cochlear implant is similar to the surgery that is done for chronic ear infections. The skin incision is made behind the ear. A special instrument is placed on the patient’s face to monitor the facial nerve. The mastoid bone (bone behind the ear) is then removed with a high speed surgical drill. An area of bone above the ear is also removed in order to make room for the internal receiver of the cochlear implant. An area called the facial recess is then uncovered to reveal an area of the inner ear called the round window.
A microscope drill is used to open this window and enter the cochlea. The electrode is then inserted through the facial recess into the round window and into the cochlea. The surgeon uses both visual and tactile information to ensure that the electrode is in proper position and that a full insertion of all electrodes has been achieved. The round window and facial recess are then packed with a small plug of muscle to insure that the electrode array stays in place.
At this point the skin incision is partially closed to allow the surgical and audiologic team to test the implant. In the unlikely event that a problem with the implant or its placement is detected it can be remedied.
After the incision is closed, a sterile dressing is placed in the incision, and the patient is taken to recovery. Initial healing takes several days, after which the patient is allowed to get the incision wet. Full healing takes several weeks to months. Initial programming of the implant takes place 4-6 weeks after surgery.
For more information on cochlear implants, please visit the manufacturers’ websites:
Cochlear Corporation – www.cochlear.com
Advanced Bionics Corporation – www.bionicear.com
Med-El Corporation – www.medel.com