Auditory System Hearing Disorders Otosclerosis

What is otosclerosis? Otosclerosis is the abnormal growth of bone in the middle ear, which can damage structures and alter mechanical hearing transmission. Definitive causes of otosclerosis currently remain unknown.

The structures of the human ear work as a chain to process sound. Sound waves are transmitted through the outer ear canal, which works as a funnel. The tympanic membrane, or eardrum, vibrates when sound hits it. Three tiny bones in the middle ear form a chain and connect the eardrum to the cochlea (the hearing structure in the inner ear). Otosclerosis affects these small bones, impeding their ability to transmit sound information to the inner ear.

Transferring Sound information from the Middle to the Inner Ear

The middle ear contains three small bones called the “ossicles.” These bones are called the:

  • Incus (or anvil)
  • Malleus (or hammer)
  • Stapes (or stirrup).

The malleus is connected to the eardrum at one end, and to the incus at the other end. The incus is connected to the stapes. The stapes, the smallest of these three bones, resembles a stirrup, with a curved portion attached to a baseplate or footplate. This footplate inserts into a small hole in the cochlea known as the “oval window.” The eardrum transfers movement to the ossicles, and the stapes, the final bone in the chain, displaces the fluid in the cochlea. This fluid movement moves the hair cells in the cochlea, which send nerve impulses to the brain.

How does Otosclerosis Affect Hearing Structures?

The bony growths that occur in people with otosclerosis affect the ossicles, and in particular, the stapes. Excess bony growth on the stapes can lead it to become fixed in the oval window, which prevents the stapes from transmitting sound information to the inner ear.

Otosclerosis - Hearing Disorders

Otosclerosis Symptoms

Gradual hearing loss is usually the first symptom of otosclerosis. Other otosclerosis symptoms can include tinnitus and balance problems.

Usually, otosclerosis leads to conductive hearing loss, which is a difficulty in the outer or middle ear, the portion of the hearing mechanism that conducts sound through the air. More rarely, it can also lead to sensorineural hearing loss. This is likely if bone growth occurs in the cochlea. Hearing loss can become severe if the bony lesions progress. An audiologist can test your hearing acuity and the functioning of your hearing mechanism.

Treatment of Otosclerosis

Exploratory surgery may be necessary to confirm an otosclerosis diagnosis, as many factors can lead to conductive hearing loss. Otosclerosis is sometimes treated surgically with a stapedectomy. Abnormal and damaged bone is removed, and synthetic replacement materials replace it to restore movement. Several types of prostheses are available; your doctor will select the type that is best for you. Regular hearing tests are recommended for anyone with otosclerosis ear disease (even if you have had a stapedectomy) to monitor your hearing, and determine whether the condition is progressing.

Resources

Massachusetts Eye and Ear Infirmary (n.d.). Otosclerosis. Retrieved February 11, 2010, from Massachusetts Eye and Ear Infirmary Web site: http://www.masseyeandear.org/for-patients/patient-guide/patient-education/diseases-and-conditions/otosclerosis/.

National Institute on Deafness and Other Communication Disorders (n.d.). Otosclerosis. Retrieved February 11, 2010, from National Institute on Deafness and Other Communication Disorders Web site: http://www.nidcd.nih.gov/health/hearing/otosclerosis.asp.

University of California at San Diego Medical Center (2006). About otosclerosis. Retrieved February 11, 2010, from University of California at San Diego Web site: http://health.ucsd.edu/specialties/surgery/otolaryngology/ear/otosclerosis.htm.