The Cochlear implant is an extraordinary technology that has significantly improved the lives of tens of thousands of children and adults with severe to profound hearing loss who do not derive enough benefit from hearing aids. While results may vary, the majority of people who receive cochlear implants are able to hear well enough to use hearing to understand speech and to talk on the telephone. Most young children hear well enough to learn spoken language and be successfully mainstreamed for school and play.
What is a cochlear implant, how does it work?
When a patient is told that he/she has a â€œnerveâ€ hearing loss, in truth, it is almost never the nerve that is not working. The problem almost always lies in the microscopic hair cells that convert mechanical sound to electrical energy within the organ of hearing (see "How We Hear") A cochlear implant bypasses the sick hair cells and directly, electrically, stimulates the healthy nerve endings under the hair cells.
A cochlear implant has two basic parts: an external part that is similar to a hearing aid, and an internal part called the receiver-stimulator that is surgically implanted in the bone behind the ear. The receiver stimulator has an antenna imbedded in it, with a magnet in the center of the antenna. An electrode array is connected to the front of the receiver stimulator and this electrode array is surgically implanted in the cochlea (organ of hearing). It is this electrode array that sends the electrical signal that bypasses the sick hair cells.
The external part of the cochlear implant, like a hearing aid, has a microphone to pick up sound. The sound goes into a special speech processor where a digitial signal is created. The digital signal travels through a cable to an external antenna, which has a magnet in its center. The external magnet aligns with the implanted magnet and allows the external antenna to sit directly over the internal antenna. Thus, the digital signal from the outer antenna goes through the intact skin to the inner antenna. From the inner antenna the signal goes to the speech processor which determines which electrodes in the cochlea should be stimulated (see illustration).
Who is a candidate for a cochlear implant?
There are two parts to the cochlear implant evaluation, medical and audiologic. The cochlear implant surgeon must make sure that there is no infection, tumor or other abnormality that would prevent successful implantation and use. This evaluation usually includes an xray of the inner ear. That may be a computerized tomogram (CT scan) or magnetic resonance imaging (MRI)
The second part of the evaluation is performed by the nonphysician members of the cochlear implant team and they include:
- Hearing tests: Every patient must see the audiologist and have a hearing evaluation to confirm the degree of hearing loss. Patients will be tested with their hearing aids. If the audiologist believes that the hearing aids are not performing as well as possible, of if they believe that there may be better hearing aids for the patient, the audiologist will try different hearing aids. Once it is determined that hearing aids are not providing sufficient benefit, cochlear implants are discussed.
- Speech-Language Pathologists: All children will be evaluated by speech language pathologists as part of the cochlear implant evaluation process. This evaluation helps understand the child's skills and plan for habilitation after implantation. The speech-language evaluation assesses all aspects of a child's ability to comprehend and to formulate verbal communication.
- Educational consultation: All children will receive an educational consultation as part of the implant evaluation process. This consultation is intended to assist families in obtaining the best possible services for their children. School placement, early intervention, and individual therapy will be discussed. Families will be assisted in determining which programs are best for their individual child.
- Social Worker: Families of children considering implantation will meet with a social worker to help answer questions and discuss concerns.
- Team meeting: After the evaluations are complete, the team members often meet to discuss the patient's test results. Each patient's needs and the appropriate way to address those needs is discussed.
- Device selection: Once it has been determined that a patient is a candidate for a cochlear implant, a device demonstration will be scheduled. There are multiple companies that manufacture cochlear implants and the device demonstration helps the patient and family decide which device best meets their nees.
What is involved with cochlear implant surgery?
Cochlear implant surgery is performed in the hospital, under a general anesthetic. Before surgery, every patient must obtain a medical letter of fitness for general anesthesia, from their pediatrician or family practitioner. The cochlear implant surgery takes about two to three hours. Very little hair is shaved behind the ear as the incision is small, usually just in the crease behind the ear. After surgery the patient is in the recovery room (PACU - post anesthesia care unit) for about one hour. Patients then return to the ambulatory care area and most patients are discharged on the day of the surgery.
The risks of cochlear implant surgery include:
- The risk of general anesthesia: Anesthesia risk is based upon each patient's medical history. In general, with cochlear implant surgery, the risk of anesthesia is very low. Special risks will be discussed by the anesthesiologist before surgery.
- Lack of guarantee as to hearing success with the cochlear implant: Although our expectation is that the cochlear implant will restore hearing, no guarantee can be offered as to how much hearing will be restored or how happy any given patient will be with the results.
- Risk of injury to the facial nerve: The facial nerve moves the muscles on the side of your face that controls smiling, closing the eye and wrinkling the forehead. If this nerve is injured you can have weakness or paralysis of the muscles of your face on the side of the surgery. This is a rare complication of cochlear implant surgery and is minimized by using a computer, during the surgery, to monitor the facial nerve.
- Strange tastes in the mouth: The nerve that helps provide taste to the tongue goes through the ear and is often cut during various ear surgeries and during cochlear implant surgery. Despite the fact that the nerve is cut, it usually causes no symptoms. Occasionally, there is a strange taste for several weeks. Rarely, the strange taste persists.
- Wound infection: As with any surgery, there is a small risk of postoperative infection. This may necessitate treatment with antibiotics.
- A lump behind the ear: There is the possibility that you will feel the receiver stimulator under the skin behind your ear after your cochlear implant surgery.
- Numbness around the ear: The area around your implant ear may feel numb or stiff. The usually resolves withing three months of surgery.
- Cerebrospinal fluid leakage: Rarely, a leak of cerebrospinal fluid (CSF) can occur from the inner ear. If this occurs, additional surgical treatment may be necessary.
- Tinnitus: You may develop tinnitus (ringing in the ear) after surgery.
- Dizziness: You may have some dizziness after the surgery, which is usually mild and transient.
Meningitis: There is a small increase in the incidence of meningitis in children and adults with cochlear implants. Meningitis is a bacterial infection of the membrane surrounding the brain, which can be a very serious, potentially life threatening complication. There are vaccinations available to minimize the chance of developing meningitis. The Centers for Disease Control (CDC) of the Federal Department of Health and Human Services and the American Academy of Otolaryngology - Head and Neck Surgery strongly recommend that all patients about to receive or who have received a cochlear implant be vaccinated for the bacteria that causes meningitis. There are several vaccines available, which can be administered by your primary care physician, otolaryngologist or pediatrician, one for young children and another for older children and adults. The suggested vaccines are at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5909a2.htm
What is postoperative programming (mapping)?
Patients are seen by the audiologist about three to four weeks after surgery to turn on or activate the external component of the cochlear implant. The initial visit lasts about two hours. Further appointments are scheduled as needed. The goal of programming (mapping) the speech processor is to customize the cochlear implant for each individual patient's hearing needs so that the patient hears as well as possible.