Conductive hearing loss
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|Conductive hearing loss|
|Anatomy of the human ear.|
|Classification and external resources|
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 (mixed hearing loss) or alone.
Conductive hearing loss occurs uniformly over all frequencies, resulting in sound and voices which seem faint or muffled.
For basic screening, hearing loss with a one-sided conductive component can be differentiated through the combined use of both the Weber and Rinne tests. If the hearing loss has a neural component on only one side, the Weber test, in which a tuning fork is touched to the midline of the forehead, can determine which ear is affected; the person will hear the sound softer in the affected ear. The Rinne test, which tests air conduction versus bone conduction is negative (abnormal result).
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 external 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)|
Pure tone audiometry, a standardized hearing test over a set of frequencies from 250Hz to 8000Hz, may be administered by a medical doctor or audiologist or audiometrist, with the result plotted separately for each ear on an audiogram. The shape of the plot reveals the degree and nature of hearing loss, distinguishing conductive hearing loss from other kinds of hearing loss.
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- External ear
Common causes of conductive hearing loss include:
- Cerumen (earwax) or foreign body in the external auditory canal
- Otitis externa, infection or irritation of the outer ear
- Exostoses, abnormal growth of bone within the ear canal
- Tumor of the ear canal
- Congenital stenosis or atresia of the external auditory canal (narrow or blocked ear canal).
- Perforated eardrum
- Tympanic membrane retraction
- Barotrauma unequal air 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, like swallowing, yawning, or the Valsalva maneuver.
- Middle ear
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 decreased pressure in the middle ear relative to the external ear, and this causes decreased motion of both the ossicles and the tympanic membrane.
- acute or serous otitis media
- Otosclerosis, abnormal growth of bone in or near the middle ear
- middle ear tumour
- temporal bone trauma
- direct trauma such as objects inserted forcibly down the ear canal.
- Congenital malformation of the ossicles. This can be an isolated phenomenon or can occur as part of a syndrome where development of the 1st and 2nd branchial arches is seen such as in Goldenhar syndrome, Treacher Collins syndrome, branchio-oto-renal syndrome etc.
- Superior canal dehiscence – which may require surgical correction.
Treatment falls into three modalities: surgical, pharmaceutical, and management, depending on the nature and location of the specific cause.
In cases of infection, antibiotics or antifungal medications are an option. Some conditions are amenable to surgical intervention such as middle ear fluid, cholesteatoma, otosclerosis. If conductive hearing loss is due to head trauma, surgical repair is an option. If absence or deformation of ear structures cannot be corrected, or if the patient declines surgery hearing aids, which amplify sounds are a possible treatment option. Bone conduction hearing aids are useful as these deliver sound directly, through bone, to the cochlea or organ of hearing bypassing the pathology. These can be on a soft or hard headband or can be inserted surgically, a bone anchored hearing aid, of which there are several types. Conventional air conduction hearing aids can also be used.
- "Hearing Loss". HealthCentral. Retrieved 8 June 2013.
- 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.