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How does otosclerosis affect air-conduction and bone-conduction test results?
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audiology
Learn about the audiology department of the Center for Audiology, Speech, Language, and Learning, a nonprofit clinic at Northwestern University, Evanston, Illinois.
In the context of audiology, otosclerosis is a condition characterized by the abnormal growth of spongy bone in the middle ear, which often leads to the fixation of the stapes (stirrup) bone. This fixation prevents the stapes from effectively conducting sound energy from the eardrum to the inner ear, resulting in conductive hearing loss.12
When performing audiometric testing, this condition produces a distinct pattern in test results:
- Air-Conduction: Because the middle ear mechanism is impaired, air-conduction thresholds show a significant loss, as sound cannot be efficiently transmitted through the ossicular chain.12
- Bone-Conduction: Bone-conduction thresholds typically remain better than air-conduction thresholds because sound bypasses the middle ear and is transmitted directly to the inner ear through the bones of the skull.23
- Air-Bone Gap: The difference between the air-conduction and bone-conduction thresholds is known as the air-bone gap. This gap serves as a measure of the transmission loss across the middle ear and indicates the potential for improvement through corrective surgery, such as a stapedectomy.42
If the disease progresses to affect the cochlea, sensorineural hearing loss may also occur, which can eventually diminish bone-conduction sensitivity as well.12