Ask the doctors: Cochlear implants target inner hearing structures

Dear Doctors: I am 45 years old and have sudden sensorineural hearing loss that is significant. There is no known cause. I’m told that the only option now or in the future is a cochlear implant. How do they work? How do I know if I might be a candidate for this type of treatment?

Dear Reader: When someone experiences sensorineural hearing loss, it is due to changes that have taken place in the structures of the inner ear or the auditory nerve. When this progresses rapidly, often over the course of 24 hours, it is known as sudden sensorineural hearing loss, or SSHL. This type of hearing loss is often caused by a viral or bacterial infection. Head trauma, autoimmune diseases and some drugs can also play a role.

The part of the inner ear most often associated with SSHL is the cochlea. It is a fluid-filled chamber lined with thousands of tiny hair cells. Two different types of hair cells work to either collect or amplify the vibrations collected and delivered by the outer and middle ear. These vibrations are converted to electrical impulses by a network of nerve endings. The auditory nerve then carries the electrical impulses to the brain, which translates them into the sounds around us.

When hearing loss involves the cochlea, a cochlear implant can be an option. It is an electronic device that bypasses the damaged portion of the inner ear and directly stimulates the auditory nerve. The implant itself consists of two portions, one outside the skull and the other within the inner ear. The outer portion has two parts: A small sound processor, which is typically positioned behind the outer ear, collects vibrations and sends them to a tiny receiver, also often located behind the ear.

The receiver collects input from the sound processor and converts it into electrical impulses. These are sent via a thin wire to a series of electrodes that have been surgically implanted into the cochlea. As those electrodes collect the electrical impulses, they send them onward to the auditory nerve for delivery to, and processing by, the brain.

Cochlear implants are intended for use by adults and children whose hearing loss ranges from moderate to severe and cannot be significantly improved with the use of a hearing aid. The person must also be physically able to undergo surgery. The procedure, which is done under general anesthesia, takes about two hours. The surgeon guides the electrodes to the cochlea via an opening they have created in the mastoid bone. The electrodes are then implanted into the cochlea. Patients return home the same day. Following a two- to four-week healing period, the implants are activated, and the outer components are put in place.

It is important to understand that cochlear implants can’t replicate natural hearing. People describe the resulting sounds as mechanical and robotic. There is often a learning curve in getting used to the devices. If your doctor has determined that cochlear implants can help you, and that you are healthy enough for surgery, it is likely you are a candidate for the procedure.

Send your questions to askthedoctors@mednet.ucla.edu.