Hearing loss affects the ability to perceive sounds and is broadly categorized into two main types. Sensorineural hearing loss involves issues with the inner ear or the auditory nerve. Conductive hearing loss involves a mechanical problem that blocks sound transmission before it reaches the inner ear structures. This impairment arises from various issues in the outer or middle portions of the ear.
Understanding Conductive Hearing Loss
Hearing relies on sound waves traveling efficiently through the ear canal and middle ear before reaching the inner ear. Sound waves enter the ear canal and cause the tympanic membrane, or eardrum, to vibrate. These vibrations are then transferred across the middle ear space by three tiny bones, known as the ossicles.
Conductive hearing loss occurs when a physical obstruction or damage to these outer or middle ear components prevents sound energy from reaching the inner ear. This disruption reduces the volume of sound transmitted, making incoming sounds appear muffled or quieter. Since the problem is mechanical, the inner ear and auditory nerve function normally, meaning the loss affects loudness rather than clarity.
Primary Sources of Obstruction and Damage
A frequent and easily treatable cause is the impaction of earwax (cerumen) within the ear canal. When earwax completely blocks the canal, it forms a physical barrier preventing sound waves from reaching the eardrum. This blockage often results in a sudden loss of hearing and a feeling of fullness.
Fluid accumulation is the most common middle ear cause, often resulting from otitis media with effusion, prevalent in young children. The presence of fluid, sometimes called “glue ear,” dampens the movement of the eardrum and ossicles, impeding sound transfer.
A hole in the eardrum, known as a perforation, also disrupts the system by preventing effective vibration. Perforations can be caused by trauma, severe infection, or changes in air pressure.
Disorders affecting the ossicles can also cause hearing loss. Otosclerosis involves abnormal bone growth around the stapes bone, causing it to become fixed. This prevents the stapes from vibrating and passing sound to the inner ear, resulting in progressive hearing loss. Trauma, infection, or cholesteatoma can also damage or dislocate the ossicles, interrupting sound transmission.
Resolving Conductive Hearing Loss
Diagnosis typically begins with a physical examination of the ear canal and eardrum, followed by formal hearing tests. An audiogram measures how well a person hears through both air conduction and bone conduction, which helps differentiate a conductive problem from a sensorineural one. Tympanometry measures the mobility of the eardrum to confirm if fluid or pressure issues are present in the middle ear.
A positive outlook often accompanies this diagnosis, as it is frequently temporary or correctable. Treatment depends on the underlying cause. Impacted earwax can be quickly removed, often restoring hearing immediately. Infections like otitis media are treated with antibiotics or, in persistent cases, small surgical drainage tubes to remove middle ear fluid.
More complex causes often require surgery, such as tympanoplasty to repair a perforated eardrum or stapedectomy to replace the fixed stapes bone in otosclerosis. For cases that cannot be corrected, a bone conduction hearing device may be used to bypass the outer and middle ear entirely, sending vibrations directly to the inner ear. This treatability contrasts with sensorineural hearing loss, which is usually permanent because it involves damage to the inner ear nerves.