Conductive hearing loss

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

 * Cerumen (earwax)
 * Otitis externa (ear infection)

Uncommon

 * Foreign body in the external auditory canal (not always)
 * Exostoses
 * Tumour of the ear canal
 * Congenital atresia

Tympanic membrane

 * Tympanic membrane perforation
 * 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.

Common
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.


 * Acute otitis media
 * Serous otitis media

Uncommon

 * Cholesteatoma
 * Otosclerosis
 * Middle ear tumour
 * Temporal bone trauma

Common
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.

Uncommon

 * Superior canal dehiscence syndrome

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.

Table 1. A table comparing sensorineural hearing loss to conductive