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Cochlear Implants

The cochlear implant is a device used to treat patients with severe to profound sensorineural hearing loss. Patients who once relied on hearing aids for help with lip reading now can hear and understand spoken language when treated with the cochlear implant.

Cochlear implant components
Multichannel cochlear implants currently are available through the ENT and Allergy Center of Missouri or University Physicians Audiology Clinic. A typical cochlear implant consists of two main parts:

Internal cochlear implant components
- Electrode array that is surgically implanted into the cochlea
- Receiver/stimulator that rests in the mastoid bone under a skin flap
External cochlear implant components
- Transmitting coil that is magnetically connected to the receiver/stimulator in the mastoid area
- Small microphone
- Body-worn or ear-level speech processors

How the cochlear implant works
The cochlear implant electronically stimulates the auditory nerve, in contrast to the usual process of acoustical stimulation. Sound is picked up by the microphone and sent by a cord to the speech processor, where the sound is encoded. The signal then is sent back by the cord to the transmitter. Next, the transmitter sends the signal as a radio signal to the receiver/stimulator. The receiver/stimulator sends the signal by an internal wire to the electrode array. Finally, the array stimulates the auditory nerve.

Cochlear implant team
The cochlear implant team thoroughly evaluates each implant candidate. The team consists of an otologist, a clinical audiologist and a psychologist. Post-implant training typically is performed by the audiologist and/or a speech pathologist.

Criteria for referral
General guidelines for implant referral vary between adults and children. Adults should be at least 18 years old. They should have bilateral, severe to profound sensorineural hearing loss, 70 decibels or greater, in at least the mid- and high frequencies. Some adults can have better thresholds of 40 to 70 decibels in the lower frequencies. To be referred for the implant, adults' speech understanding should be poor without hearing aids, as measured by a recorded version of the HINT test during a routine audiological evaluation. Patients should have a bilateral, severe to profound sensorineural hearing loss in at least the mid- and high frequencies. Children with bilateral profound sensorineural hearing losses as young as 12 months old can now be implanted.

Additional criteria for both adults and children may include the following:
Minimum or no benefit previously derived from appropriately fitted hearing aids. "Benefit" is determined by a patient's ability to understand speech with and without hearing aids. This qualification is determined by speech perception tests performed by the audiologist on the cochlear implant team. Patients could be peri- or postlinguistically deafened (i.e., loss of hearing before, during or after the acquisition of language).

Contraindications for referral
The only condition that may preclude patients from being referred for a cochlear implant is deafness as a result of an acoustic nerve lesion, such as an acoustic tumor. Patients with possible complicating factors, such as ossification of the cochlea or chronic middle ear problems, will be evaluated on a case-by-case basis by the implant team.

Expected performance in adults
The performance of adult cochlear implant recipients varies from patient-to-patient. Performance is influenced by the following factors: when deafness occurred, number of years of deafness, amount of time spent without appropriate hearing aids, cognitive abilities and motivation to be part of the hearing world.

At the very least, patients can expect ease in speech reading, to hear environmental sounds, to monitor their voice and to feel less isolated. These results are typical of both pre- and perilinguistically deafened adults.

Many patients, typically the postlinguistically deafened adults, do much better. They can understand a great deal of speech without lip reading. In addition, 30 percent to 40 percent of patients can use the telephone.

Expected performance in children
Cochlear implant performance in children varies more than that of adults but is influenced by the same factors. An important variable in children is the type of education they receive. In order to hear, learn and use spoken language, children ideally should be in an educational and home environment where spoken language is the primary form of communication.

Depending on these factors, children can be expected to understand and use spoken language to various degrees, with and without lip reading. With the cochlear implant, their speech-production skills will improve, their voice quality will be better and they will be more aware of environmental sounds. The performance of children depends to a great extent on the post-implant training they receive. This training includes speech and language therapy, auditory training and the parents' willingness and commitment to facilitate oral/aural communication with the child.

Post-operative care
After initial activation of the implant, follow-up visits are necessary to program the speech processor and evaluate performance. Visits typically are scheduled at three-month, six-month and 12-month post-operative intervals and annually thereafter.

To contact one of our hearing specialists, please call:
(573) 882-7903 or (573) 817-3000

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