In an audiogram, a bone conduction threshold that is 15 dB better than air conduction threshold across frequencies is characteristic of which type of hearing loss?

Explanation

## Audiogram Interpretation: Air-Bone Gap **Key Point:** The air-bone gap (difference between air conduction and bone conduction thresholds) is the hallmark of conductive hearing loss. A bone conduction threshold that is better (lower/quieter) than air conduction indicates the inner ear is functioning normally, but sound transmission through the middle ear is impaired. ### Air-Bone Gap Classification | Gap Size | Interpretation | | --- | --- | | 0–10 dB | Normal or sensorineural loss | | 15–30 dB | Mild to moderate conductive loss | | >30 dB | Severe conductive loss | **High-Yield:** In conductive hearing loss: - Bone conduction (BC) thresholds remain **normal** (≤20 dB HL) - Air conduction (AC) thresholds are **elevated** (>20 dB HL) - **AC > BC** by ≥15 dB = pathognomonic for conductive loss **Clinical Pearl:** Common causes of conductive hearing loss with air-bone gap include otitis media with effusion, otosclerosis, ossicular discontinuity, and cerumen impaction. ### Why Bone Conduction is Better in Conductive Loss Bone conduction bypasses the external and middle ear entirely—sound vibrations are transmitted directly to the cochlea via skull vibration. If the cochlea is normal (as in conductive loss), BC thresholds will be normal. Air conduction, however, must pass through the impaired conductive pathway, resulting in elevated thresholds.