Cochlear Implantation

Cochlear Implants (CIs) were approved in 1990 by the Food and Drug Administration (FDA) for use in adults and children (ages 2-17) with profound hearing loss. Now, children as young as one year old are receiving CIs in one or both ears. Children with meningitis have increased risk of ossification of the inner ear and therefore, may receive a CI as young as 4-6 months old.

Candidacy Guidelines for Children and Adults:

Adult (age 18+) CI candidates should have moderate to profound hearing loss in the low frequencies, and severe-to profound hearing loss in the mid to high frequencies. A CI is approved after the patient has had at least 3-6 months of a trial period with suitable amplification (hearing aids), which showed limited benefit. Lack of development in simple auditory skills is one example of limited benefit from amplification. Adults and children alike must have a strong support system in order undergo the process of a CI. A CI requires an enormous amount of commitment from the family and child, in terms of time and effort. The family should be aware of these commitments and willing to become closely involved in the aural habilitation/rehabilitation process. Prior to the CI, parents should develop realistic expectations, and be familiar with data indicating the benefits of CI use. Once candidacy is determined, parents are responsible for making the decision whether or not to receive a CI.

Components of a Cochlear Implant:

An externally worn headset which includes a microphone placed on a behind-the-ear (BTE) style unit, and external transmitter coil that has a magnet adheres to the head over the skin. The externally worn headset is connected to a speech processor (battery source), and a surgically implanted internal receiver stimulator (CI) which is attached to the electrode array.

How does a Cochlear Implant Work?

Sound waves are picked up by the microphone located in the headset at the ear, and are converted into an electrical signal. A cord carries the sound from the microphone to the speech processor (a powerful miniaturized computer). The speech processor filters, analyzes, and digitizes the sound into coded signals and sends it to the external transmitter coil. The speech processor can be either be body-worn (like a body hearing aid), or at ear-level (like a BTE style hearing aid). The external transmitter coil sends the coded signals through the skin to the internal receiver stimulator (CI) under the skin. The internal CI (receiver stimulator) delivers the information to the array of electrodes, which is surgically implanted into the cochlea (inner ear). The electrodes along the array stimulate remaining auditory nerve fibers in the cochlea. The auditory nerve then sends the sound, via the auditory system, to the brain for interpretation. This entire process takes only microseconds.

The Cochlear Implant Team

  • ENT physician
  • Pediatrician/family practitioner
  • Audiologist
  • Speech-language pathologist
  • Psychologist
  • Teachers of the hearing impaired
  • Social workers
  • Parents

Process of Pre-implantation work-up:

The candidate or family may make initial contact with professionals from the field, and obtain information regarding topics such as the functions of a CI, candidacy, expected benefits or limitations. Pre-implant counseling provides the candidate or family with information about obtaining, maintaining, and using a CI as well as maximizing its benefits. The pre-implant counseling is very important, and may take place before or after the formal evaluation.

Audiologic Evaluation; Comprehensive Behavioral & Physiological tests

  • Complete Audiological Evaluation (CAE)
  • Auditory Brainstem Response (ABR) testing
  • Otoacoustic Emissions (OAEs) testing
  • Videonystagmography (VNG) testing
  • Assessing amplification  of high-powered Hearing Aids post-trial
  • Speech/Language testing

Medical Evaluation:

This assessment ensures that the candidate can safely undergo general anesthesia.

Imaging is taken to ensure that the cochlea is suitable for insertion of the electrode array.

Any other medical conditions that might preclude use of an implant are also ruled out at this time.

Psychological evaluations:

This evaluation ensures that the candidate and their family are highly motivated and have a positive attitude regarding the role of hearing with a CI. Ensuring realistic expectations is key in this process.

Cochlear Implant Surgery

The patient is under general anesthesia. The surgeon makes an incision behind the ear, and forms a small depression in the mastoid bone to place the CI and insert the electrode array. The electrode array is threaded via the mastoid and middle ear a cavity and then inserted in the cochlea’s scala tympani through the round window. The incision is then closed and the head bandaged. The surgery can range from 1-3 hours, and often is performed on an outpatient basis. It can take 3-5 weeks post-surgery for the incision to heal. A child will typically be sent home the same day, an adult a day or two later due to increased risk of complications. Possible potential risks related to surgeries include bleeding, injury to the facial nerve, dizziness or increase tinnitus.

Initial Stimulation Session

After the incision has healed, the patient returns to the clinic for their initial stimulation session. Prior to this session, the patient will not be able to hear with the implant. The external components are fitted on to the patient ensuring their comfort. The audiologist uses a computer and the CI’s manufacturers’ software in order to program the speech processor. In very young children, these parameters are done objectively not necessitating any feedback. However, these parameters can be difficult to obtain with young children who are able to provide feedback, and consequently the length of time required to fit a child can be varied upon their child maturity and cooperation. In most cases, objective and subjective measures are taken in all aged patients because of the valuable information they provide.

                     ***An Emergency Follow-up MUST be scheduled if the patient notes***

      • Facial stimulation
      • Intermittent signal
      • Cessation of sound
      • Change in sound quality
      • Abnormal squeaking or popping
      • Parents should be alerted to any signs such as no response from the child

Follow-up Evaluation/Fine Tuning

It takes time for the nerve to adapt and for the brain to interpret sound again. Periodical adjustments to the speech processor generally enhance performance as time passes. Monitoring CI performance and physiological changes in the auditory system is imperative for success.

Variables that Affect Success with Cochlear Implants

    • Length of deafness
    • Age of hearing loss onset
    • Length of implant use
    • Age of implantation (first and second)
    • Etiology (cause) of hearing loss, status of the cochlea and  nerve fiber survival
    • Surgical issues
    • Cochlear implant technology
    • Motivation and commitment of both  patient and family
    • Mode of communication
    • Rehabilitation/habitation methods and educational programs

Benefits from the Cochlear Implant

Although the previous factors can contribute to the benefits of the CI, exact benefits cannot be predicted for a child or adult; patients’ performances vary. Overall, this sensory prosthetic device is the most successful of all sensory prosthetic devices to date allowing adult patients with profound hearing loss the potential to hear again and for children, the potential to develop normal speech and language, literacy, social skills, and successful academia.

References:

 Schafer, E.C., & Wolfe,J (2010). Programming Cochlear Implants. Plural Publishing.

Webliography:

http://www.cochlear.com/files/assets/timeline.swf

http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ImplantsandProsthetics/CochlearImplants/default.htm

Resources! Resources! (Demoss, 2011)

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