Conductive hearing loss
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|Conductive hearing loss|
|Classification and external resources|
Anatomy of the human ear.
Conductive hearing loss occurs when there is a problem conducting sound waves anywhere along the route through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles). This type of hearing loss may occur in conjunction with sensorineural hearing loss or alone.
The Weber test, in which a tuning fork is touched to the midline of the forehead, localizes to the affected ear in people with this condition. The Rinne test, which tests air conduction vs. bone conduction is negative (abnormal result).
Common causes of conductive hearing loss include:
- Foreign body in the external auditory canal
- Tumor of the ear canal
- Congenital or Choanal atresia
- Tympanic membrane perforation
- Tympanic membrane retraction
- Membrane tension by different pressures in the external and middle ear. This can temporarily occur, for example, by the environmental pressure changes as when shifting altitude, or inside a train going into a tunnel. It is managed by any of various methods of ear clearing maneuvers to equalize the pressures.
Fluid accumulation is the most common cause of conductive hearing loss in the middle ear, especially in children. Major causes are ear infections or conditions that block the eustachian tube, such as allergies or tumors. Blocking of the eustachian tube leads to increased pressure in the middle ear relative to the external ear, and this causes decreased motion of both the ossicles and the tympanic membrane.
Severe otosclerosis, form of mechanical conductive hearing loss most commonly found in people who have been subjected to intense noise. Occurs when there is an obstruction in either the oval window and/or the round window. This type of hearing loss can usually be repaired by surgical opening of the blockage.
Conductive hearing loss is treated in varying ways, depending on the circumstances. If absence or deformation of ear structures cannot be corrected, hearing aids, which amplify sounds at preset frequencies to overcome a conductive hearing loss in that range, are a possible treatment option. In cases of infection, antibiotics or antifungal medications are an option. If conductive hearing loss is due to head trauma, surgical repair is another option. It can also be treated with cochlear implants, which stimulate cochlear nerves directly, consisting of both internal and external components.
Hair cell regeneration using stem cell and gene therapy is years or decades away from being clinically feasible, and such operations are only performed in the United States, Canada, and the United Kingdom as part of medical research. However, studies are currently underway on the subject; the first FDA-approved trial for treatment of sensorineural hearing loss began in February 2012.
Differentiating conductive and sensorineuronal hearing loss
When a Weber test is carried out, sound localizes to the ear affected by the conductive loss. A Rinne test, in which air conduction is normally greater than bone conduction, is usually negative (abnormal – note unusual terminology here compared with other medical tests), and shows greater bone conduction than air conduction.
The following table compares sensorineural hearing loss to conductive:
|Criteria||Sensorineural hearing loss||Conductive hearing loss|
|Anatomical site||Inner ear, cranial nerve VIII, or central processing centers||Middle ear (ossicular chain), tympanic membrane, or inner ear|
|Weber test||Sound localizes to normal ear||Sound localizes to affected ear (ear with conductive loss)|
|Rinne test||Positive Rinne; air conduction > bone conduction (both air and bone conduction are decreased equally, but the difference between them is unchanged).||Negative Rinne; bone conduction > air conduction (bone/air gap)|
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- Page 152 in:Rex S. Haberman (2004). Middle Ear and Mastoid Surgery. New York: Thieme Medical Pub. ISBN 1-58890-173-4.
- Ruben, Robert J. (April 2007). "Hearing Loss and Deafness". The Merck Manual. Retrieved 8 June 2013.
- "Types, Causes and Treatment". Hearing Loss Association of America. Retrieved 8 June 2013.
- "Sensorineural Hearing Loss". HealthCentral. Retrieved 8 June 2013.
- Parker, M. A. (2011). "Biotechnology in the Treatment of Sensorineural Hearing Loss: Foundations and Future of Hair Cell Regeneration". Journal of Speech, Language, and Hearing Research 54 (6): 1709–1731. doi:10.1044/1092-4388(2011/10-0149). PMC 3163053. PMID 21386039.
- "Study Using Stem Cells to Treat Sensorineural Hearing Loss Underway". HealthyHearing. 2 February 2012. Retrieved 8 June 2013.