## Audiogram Patterns in Conductive Hearing Loss **Key Point:** Conductive hearing loss is characterized by a pathognomonic air-bone gap on audiometry, where air conduction (AC) thresholds are worse (elevated) than bone conduction (BC) thresholds. ### Mechanism In conductive hearing loss, the middle ear or external ear pathway is impaired, preventing efficient transmission of airborne sound. However, bone conduction bypasses the middle ear entirely via direct vibration of the cochlea, so BC thresholds remain normal or near-normal. ### Audiogram Interpretation | Finding | Conductive Loss | Sensorineural Loss | Mixed Loss | |---------|-----------------|-------------------|------------| | Air conduction (AC) | Elevated (worse) | Elevated (worse) | Elevated (worse) | | Bone conduction (BC) | Normal | Elevated (worse) | Elevated (worse) | | Air-bone gap | Present (>15 dB) | Absent (<10 dB) | Present (>15 dB) | | Carhart's notch | Absent | Absent | May be present | **High-Yield:** The air-bone gap is the hallmark of conductive hearing loss and is defined as AC threshold minus BC threshold >15 dB at any frequency. **Clinical Pearl:** Common causes of conductive hearing loss include otitis media with effusion, otosclerosis, cerumen impaction, and ossicular chain discontinuity. The audiogram alone cannot identify the cause but confirms the site of lesion (conductive vs. sensorineural). **Mnemonic:** **ABC** — **A**ir worse than **B**one = **C**onductive loss. 
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