DEAR DOCTOR K:
I’ve been gradually losing my hearing. My doctor says he can restore my hearing with a procedure called stapedectomy. Can you tell me about it?
To answer your question, I need to explain how you hear. It is an amazing process. Sound travels in waves through the air into your ear canal. Inside the ear canal, the sound waves are amplified. The waves strike your eardrum. The eardrum is a thin membrane, similar to the wall of a balloon.
Right behind the eardrum is a group of tiny bones called ossicles. When the sound waves cause the eardrum to vibrate, the vibration is transmitted to the tiny bones. These bones then transmit the vibrations through fluid in a part of your inner ear called the cochlea. Inside the cochlea are tiny hairs. Vibrations in the fluid are transmitted to the hairs. When the hairs vibrate, signals are sent up the main nerve for hearing. Those signals then land in a part of the brain where the signal is received and interpreted.
Why is the way we hear so complicated? Don’t ask me, I didn’t design it. But I count myself lucky every day that I can hear.
Not surprisingly with such a complex process, many things can go wrong. For example, hearing loss can occur when something blocks sound waves from passing through the outer or middle ear. The source of the obstruction can be any number of things: earwax, fluid, inflammation, a cyst or other abnormal growth, or something accidentally lodged in the ear. Not unexpectedly, this happens more often in infants than in adults. But I once saw a man in his 50s who was having trouble hearing in his left ear. It turned out he had the cotton from the end of a Q-tip stuck inside his ear canal.
The obstruction can also be caused by otosclerosis, which is most likely the cause of your hearing loss. Otosclerosis is the abnormal growth of the tiny ossicle bones. It usually occurs on the stapes, the smallest ossicle in the middle ear. Hearing loss occurs because the stiffened stapes can no longer vibrate and pass sound waves from the ear canal to the inner ear.
Stapedectomy can correct otosclerosis. Working through the ear canal, the surgeon removes all or part of the stapes. He or she replaces it with an artificial stapes that can vibrate. (I’ve put an illustration of this procedure below.)
An abnormal bone growth, as shown in the top figure (A), sometimes prevents the stapes from vibrating and passing sound waves to the inner ear. To correct this condition, the surgeon removes the stapes bone and replaces it with a prosthesis (B). After surgery, sound waves pass through the eardrum, vibrating it. The vibrations pass to the malleus and then the incus, which is connected to the prosthesis. These vibrations cause the prosthesis to move, and the sound waves pass into the inner ear.
A major risk of stapedectomy is hearing loss, which can be total. Some doctors will not operate until the hearing loss is great enough to justify the risks of surgery.
With newer techniques and materials, the risks of this operation are not as great as they used to be. Still, it’s important to discuss the risks and benefits with your doctor. If you decide to go ahead with it, choose a surgeon who performs this operation frequently.