Otosclerosis
Otosclerosis is a condition which leads to a gradual loss of hearing in one or both ears. It usually affects young caucasian females. This condition is believed to arise from a genetic disorder which can be inherited from generation to generation.
A brief review of the anatomy of the middle ear allows a better understanding of this disorder. Sound entering the ear canal causes vibrations of the tympanic membrane (eardrum). The tympanic eardrum is attached to one of three ossicles (bones) found in the middle ear and it is called the malleus. The malleus bone transmits the mechanical vibrations to another ossicle, the incus, which in turn transmits the vibrations to the smallest of the three ossicles, the stapes. The stapes bone vibrates and sends the message to the inner ear. The inner ear is made of a bony labyrinth filled with fluid and membranes. As the stapes vibrates, the fluid in the inner ear is set into motion. The cilia on the ends of hair cells within the inner ear are bent and an electrical signal is generated and travels along the (cochlear) hearing nerve and then back to the brain. The inner ear is composed of the cochlea, that is responsible for hearing and the semicircular canals that convey balance information concerning angular acceleration of the head back to the brain.
In otosclerosis, the bone around the junction of the stapes and the inner ear is affected. The stapes becomes more and more fixed with time, so much so that the sound entering the ear canal can not conduct across the ossicles to the inner ear. The clarity with which a person can hear with otosclerosis is extremely good provided the sound is loud enough.
There are three options in the management of otosclerosis. The first involves no treatment and coping with the degree of hearing loss that is present and following the hearing with serial audiograms. The second form of management is the use of a hearing aid. Hearing aids have been found to be very useful in otosclerosis.
The third form of treatment involves a delicate operation called a stapedectomy. This operation can be done under either local anesthesia with medication given intravenously for sedation or under general anesthesia. Patients either go home the same day or spend one night in the hospital.
The entire operation is performed through the ear canal through a operating microscope. A skin incision is made in the ear canal and the eardrum is elevated . A small nerve called the chorda tympani which transmits taste information from t he front 2/3 of the tongue frequently has to be mobilized to allow adequate visuali zation of the stapes. Temporary taste disturbance is not uncommon after this operation. The bone around this nerve has to be removed with fine instruments. The ossicles are then examined and the joint between the incus and stapes is severed. A laser is used to divide a tendon which holds the stapes in place. The stapes is then fractured and removed. A laser is then used to make a hole in the footplate whic h separates it from the inner ear. I prefer to then use a piece of vein harvested from the hand to cover the opening to the inner ear. A small prosthesis is then inserted over the vein graft and attached to the incus.
There are two basic techniques used in otosclerosis surgery:
The small fenestra technique involves making a small hole in the footplate and inserting a prosthesis through that hole.
The wide fenestra technique involves removing as much of the footplate that will easily come out. A graft is then placed over the oval window and a prosthesis is then placed over the graft.
The hearing after a stapedectomy may be muffled because of some blood that may have collected around the prosthesis. During the two to three weeks following the operation, patients usually hear pops and crackles when they yawn or swallow. The eustachian tube opens with these events and the fluid in the middle ear usually clears thereafter. As the fluid clears, the hearing becomes clearer.
Most patients experience some dysequilibrium after the operation which lasts from 24 to 48 hours.
The results for hearing are astonishing. 95% of patients who have a stapedectomy done for the first time have normal hearing after the operation. The improved hearing usually lasts for 20 years plus. The results for hearing after a revision operation are much less at 50%. However most patients after having a revision operation do report improvement in their hearing.
It must be remembered that not all otolaryngologists or ear, nose and throat physicians perform this operation on a regular basis. Most physicians who perform this type of operation have successfully completed a one or two year fellowship in neurotology and limit their practice to ear surgery.