Two Categories of Hearing Loss: Conductive and Sensorineural

Doctors divide the causes of hearing loss into two categories: conductive hearing loss and sensorineural hearing loss.

Conductive hearing loss is reduced conduction (transmission) of the vibrations of sound waves to the inner ear. It generally results from a problem with the outer or middle ear. Typical causes of conductive hearing loss among adults are blockage of the ear canal by earwax, stiffening of the ossicles by scar tissue that results from middle ear infection or surgery, and fluid accumulation in the middle ear due to a blocked eustachian tube.

Sensorineural hearing loss is an inability to sense sounds once they have reached the cochlea. It can result from disorders that damage the hairlike projections in the inner ear, the auditory nerve, or parts of the brain that decode and interpret sounds. In addition to aging itself, nerve damage due to tumors or strokes can cause sensorineural hearing loss.

Very often, hearing loss is both conductive and sensorineural. Otosclerosis is a condition in which one of the ossicles stiffens, causing conductive hearing loss. But otosclerosis may also cause sensorineural hearing loss by affecting the bone of the cochlea. Changes in the skull and temporal bone due to Paget's disease can cause both conductive and sensorineural hearing loss.

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