Conductive Hearing Loss

Conductive hearing loss occurs when sound is blocked or attenuated as it passes through the outer ear canal, eardrum, or middle-ear ossicles before reaching the cochlea. Because the inner ear and auditory nerve are intact, sound delivered directly to the cochlea by bone conduction is preserved, producing the characteristic air-bone gap on the audiogram. Common causes include earwax impaction, middle-ear fluid, eardrum perforation, and otosclerosis.

Definition

Conductive hearing loss is a reduction in hearing caused by impaired transmission of sound through the outer or middle ear, with a preserved cochlea, characterized audiometrically by an air-bone gap in which bone-conduction thresholds are better than air-conduction thresholds.

Scope

This entry covers the anatomy of the sound-conducting apparatus, the mechanisms that impede transmission, the audiometric signature of conductive loss, and its principal causes. It treats conductive hearing loss as a category of pathology within hearing-loss classification and describes how the condition is recognized and studied, not how an individual should be evaluated or treated.

Key concepts

• Air-bone gap
• Ossicular chain (malleus, incus, stapes)
• Tympanic membrane perforation
• Otitis media with effusion
• Otosclerosis and stapes fixation
• Cerumen impaction and external-canal obstruction
• Tympanometry

Mechanisms

Sound normally passes through the ear canal, vibrates the tympanic membrane, and is transmitted by the ossicular chain to the oval window, which drives the cochlear fluids. Conductive loss arises when any step in this chain is impaired: obstruction of the canal (such as cerumen), perforation or stiffening of the eardrum, fluid in the middle-ear space, or fixation or disruption of the ossicles, as in otosclerosis where the stapes footplate becomes immobilized. Because the cochlea remains functional, bone-conducted sound bypasses the blockage, so bone-conduction thresholds stay normal while air-conduction thresholds worsen, producing the air-bone gap.

Clinical relevance

Conductive losses are important because many of their causes are mechanical and stand apart from cochlear damage in how they present audiometrically. Recognizing the conductive pattern is central to localizing where in the ear a problem lies. This description is for orientation and evidence appraisal; it is not diagnostic guidance for an individual.

Epidemiology

Otitis media with effusion is among the most common causes of conductive hearing loss in children and is a leading reason for childhood medical visits and surgery worldwide. Otosclerosis is a frequent cause of acquired conductive loss in younger and middle-aged adults, with a recognized hereditary component and variation across populations.

History

The distinction between conductive and other hearing losses was made precise by the introduction of audiometry with separate air- and bone-conduction testing, which let clinicians identify the air-bone gap as the hallmark of impaired sound conduction. The recognition of otosclerosis as a cause of stapes fixation and the surgical approaches developed to address it were landmarks in understanding and managing conductive loss.

Key figures

• Anne G. M. Schilder
• Lisa L. Cunningham
• Debara L. Tucci

Seminal works

• cunningham-2017
• schilder-2016
• batson-2017

Frequently asked questions

What distinguishes conductive from sensorineural hearing loss on an audiogram?

Conductive loss shows an air-bone gap, meaning bone-conduction thresholds are better than air-conduction thresholds because the cochlea is intact, whereas sensorineural loss reduces both together with no gap.

Is conductive hearing loss often reversible?

Many causes of conductive loss are mechanical, and as a category it frequently has identifiable structural origins; whether any individual case can be addressed is a clinical judgement outside the scope of this reference entry.