What is Otosclerosis

Otosclerosis is a disease of the middle ear bones and sometimes the inner ear. Otosclerosis is a common cause of hearing impairment and is rarely hereditary.

How Does a “Normal” Ear Function?

The ear is divided into three parts; the external ear, the middle ear, and the inner ear. The external ear collects sound, the middle ear mechanism transforms the sound and the inner ear receives and transmits the sound.

Sound vibrations enter the ear canal and cause the eardrum to vibrate. Movements of the eardrum are transmitted across the middle ear to the inner ear fluids by three small ear bones. These middle ear bones (hammer or malleus, anvil or incus and stirrup or stapes) act as a transformer changing sound vibrations in air into fluid waves in the inner ear. The fluid waves stimulate delicate nerve endings in the hearing canals. Electrical impulses are transmitted on the nerve to the brain where they are interpreted as understandable sound.

process of hearing

What Are the Types of Hearing Impairment?

The external ear and the middle ear conduct sound; the inner ear receives it. If there is some difficulty in the external or middle ear, a conductive hearing impairment occurs. If the trouble lies in the inner ear, a sensorineural or nerve hearing impairment is the result. When there is difficulty in both the middle and the inner ear a mixed or combined impairment exists. Mixed impairments are common in otosclerosis.

otosclreosis diagnosis

Hearing Impairment from Otosclerosis

If we had been able to examine your middle ear under the microscope before a hearing impairment developed we could have seen minute areas of both softening and hardening of the bone. This process may spread to the stapes, the inner ear, or to both sides.

Stapedial Otosclerosis

Usually otosclerosis spreads to the stapes or stirrup none, the final link in the middle ear transformer chain. The stapes rests in the small groove, the oval window, in intimate contact with the inner ear fluids. Anything that interferes with its motion results in a conductive hearing impairment. This type of impairment is called stapedial otosclerosis and is usually correctable by surgery.The amount of hearing loss due to involvement of the stapes and the degree of nerve impairment present can be determined only by audiometric examination (hearing tests).

Cochlear Otosclerosis

When otosclerosis spreads to the inner ear a sensorineural hearing impairment may result due to interference with the nerve function. This nerve impairment is called cochlear otosclerosis and one it develops it may be permanent. On occasion the otosclerosis may spread to the balance canals and may cause episodes of unsteadiness.