Cochlear implant

Information

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 - but they generally consist of several similar parts. One part of the device is surgically implanted into the temporal bone (the bone surrounding the ear). This device consists of a receiver-stimulator, which accepts, decodes, and then transmits an electrical signal to the brain.

The second part of the cochlear implant is an external device. This consists of a microphone/receiver, a speech processor, and an antenna. This portion of the implant receives the sound, converts the sounds into an electrical signal, and transmits it to the internal portion 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 re-establish normal hearing - they are tools that allow for sound and speech input to be processed and transmitted to the brain.

The criteria used to select appropriate candidates for cochlear implants are changing over time - as both the technology changes, and our understanding of the auditory (hearing) pathways in our brain improves.

Both children or adults can be candidates for cochlear implantation. They can be born deaf, or may have become deaf after learning to speak. Children as young as 1 to 1.5 years old are now becoming candidates for this surgery. Although adult and pediatric criteria are slightly different, they are based upon several similar guidelines:

  1. The patient should be completely or very-near completely deaf in both ears, and received almost no improvement after trying hearing aids. Anyone who has adequate hearing with hearing aids is not a good candidate for cochlear implants.
  2. The patient needs to be highly motivated, because after the cochlear implant is placed, there is a significant amount of learning that needs to occur in order to make proper use of 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 sound-processing skills.
  5. In order to determine if a patient is a surgical candidate, the patient must have a medical evaluation by an otolaryngologist (ear, nose, and throat doctor). This evaluation may include a CT scan or an MRI scan to evaluate the structures of the brain, and the middle and inner ear.
  6. Patients (especially children) may need psychological evaluation to determine if they are a candidate for surgery.

HOW IT WORKS

In a normal ear, sounds are transmitted through the air, causing the eardrum and then the ossicles (middle ear bones) to vibrate. This sends a vibratory wave into the cochlea (inner ear). 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 transforming mechanical energy (sound) into electrical energy, which 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 components. Sound is picked up by a microphone worn near the ear. This sound is then transmitted to a speech processor worn on the body, usually on a belt. The sound is then analyzed and converted into electrical signals - which are transmitted to a surgically implanted receiver behind the ear. This receiver then sends the signal through an electrode array (wire) into the inner ear, where the electrical impulses are transmitted to the brain.

HOW IT IS IMPLANTED

Surgery for inserting a cochlear implant is performed with the patient fully asleep. An incision is made behind the ear, sometimes after shaving a portion 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 internal part of the implant to be inserted.

The electrode array is then passed into the cochlea (inner ear). The receiver is placed into a “well” created behind the ear to help keep it in place, and to make sure it is close enough to the skin to allow transmission of electrical information from the external portion of the device.

After surgery, there will be stitches behind the ear, and you may be able to feel the receiver in its “well” behind the ear. Any shaved hair should grow back. The external portion of the device will be placed about 3 to 4 weeks after surgery, to give the incision time to heal.

RISKS OF SURGERY

Cochlear implant is a relatively safe surgery. As with all surgeries, there are potential risks. The most common complications include 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 that surrounds the brain (cerebrospinal fluid)  
  • Temporary vertigo (dizziness)  
  • Failure of the device to work

RECOVERY AFTER SURGERY

After surgery, most patients are admitted to the hospital overnight for observation. Patients are given pain medicines and sometimes antibiotics to help with healing after surgery. Many surgeons will place a large dressing over the operated ear, which will be changed the day after surgery.

Several weeks after surgery, the external portion of the cochlear implant is magnetically secured to the receiver-stimulator that was implanted behind the ear. It is only at this point that the device will begin to be usable.

Once the incision site is well healed, and the implant is secured to the external processor and antenna, patients will begin to work with a combination of audiologists, speech therapists, otolaryngologists (ear, nose, and throat doctors), and possibly other specialists in order to learn to “hear” and process sound using the cochlear implant. This is an extremely important part of the process, as it requires a coordinated effort between patient and the team of specialists in order to achieve maximum benefit from the implant.

Results in patients using cochlear implants vary greatly, and may be due partly to the condition of the nerve for hearing prior to surgery, the mental abilities of the patient, the device being used, the length of time that the patient was deaf, and the surgery itself.

Some patients can learn to communicate on the telephone, whereas others can only recognize sound. Achieving maximal results can take several years, and requires motivation on the part of the patient. Patients are often enrolled in programs to help with rehabilitation of hearing and speech.

LIVING WITH AN IMPLANT

Once full healing has occurred, there are few absolute restrictions for cochlear implant users. Most activities are acceptable, although some physicians recommend avoiding full-contact sports, in order to lessen the chance of trauma to the implanted device.

Most patients with cochlear implants cannot get MRI scans, as the implant is metallic.

Johns Hopkins patient information

Last revised: December 3, 2012
by Gevorg A. Poghosian, Ph.D.

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