Cochlear Implants

Overview

Cochlear implants are an option for those with severe to profound sensorineural hearing loss in which hearing aids are providing little or no benefit. A cochlear implant consists of two parts. The first part is an internal component that is surgically implanted into the cochlea and skull. The second part is the external device that acts as a microphone and processor that transfers the sound through the skin into the internal device by way of an electromagnet that sits on the skin over the internal device. The reader is referred to the websites of the manufacturers (Advanced Bionics Corporation, Cochlear Americas, and MedEl Corporation) for a detailed discussion of the surgical procedure, and pictures of the device, as well as a more detailed discussion of this topic. The following discussion is a simple summary.

Candidacy

Age 12 months or older,
Severe to profound sensorineural hearing loss,
Little or no benefit from appropriate hearing aids,
Presence of a cochlear nerve and cochlea (may be incompletely formed).
No contraindications to general anesthesia.

A medical work-up by the implant team usually includes special hearing testing, a CT scan and MRI scan of the head, and speech therapy evaluation. Most insurance companies require meeting Food and Drug Administration requirements based on this workup before they will approve proceeding with surgery.

Surgery

Surgery is an approximately one hour procedure under general anesthesia in which the internal device is implanted in the cochlea and skull behind and above the ear. This is routinely performed in an outpatient surgical facility in both children and adults. Surgical complication rates are no greater than other elective surgical procedures (less than 5 percent).

Recovery

A typical recovery period of 4-6 weeks before the implant is used allows for complete healing of the implant site and has virtually eliminated wound healing problems seen in the earlier days of implantation.

Turning on the Implant

Called mapping, this involves programming the implant for maximal hearing for each individual person. The implant is much more sophisticated than a hearing aid and extremely flexible in providing electrical stimulation to the cochlea. The audiologists work closely with the patient and the speech therapist to provide the best “map” for that individual. Also, the map typically changes over time as the patient learns to hear from the implant. Different programs can be used interchangeably to provide the clearest hearing in different sound environments.

Results

There are multiple factors that determine the level of hearing obtainable with a cochlear implant. The status of the cochlear nerve, position of the implanted electrodes within the cochlea, and the level of previous hearing all play a role in what the patient hears once the implant is turned on. Minimal expectations include an environmental awareness of sound and assistance with lip-reading. How clearly one hears depends primarily on whether the patient has heard well before, and how long it has been since the patient heard well. If the patient has never heard well, than the process of learning to hear can take months to years. In these patients how well you hear is often a function of how long they have been using the implant, with continued improvement over time. If the patient had heard well recently before losing their hearing, good clarity of hearing can be expected very quickly after initial mapping. Unfortunately, there are no pre-operative tests that can predict how well someone will hear after their implant. Good counseling by the implant team is extremely important pre-operatively to give the patient reasonable expectations.