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Hearing

Conductive hearing loss

The inner ear is fine; the sound is not reaching it. Conductive hearing loss is the kind that mechanics — and therefore surgery — can address.

Audiogram Pure-tone audiogram showing air conduction thresholds around 40 to 50 decibels and bone conduction thresholds around 10 to 25 decibels. The shaded area between them is the air-bone gap. 0 20 40 60 80 100 120 250 500 1k 2k 4k 8k Frequency (Hz) Hearing level (dB HL) <<<<< air-bone gap
Air conduction <Bone conduction Air-bone gap

What it is

Conductive hearing loss is a failure of transmission. Somewhere between the ear canal and the inner ear, sound is blocked, dampened or disconnected. Sounds become quieter but, because the cochlea is healthy, they stay clear: make them loud enough and they are heard normally. This is why conductive losses respond so well to amplification, and why people with them often hear better in noise than expected.

The air-bone gap

On the audiogram, air-conduction thresholds (sound through the whole ear) are worse than bone-conduction thresholds (sound delivered directly to the inner ear through the skull). The difference, in decibels, is the air-bone gap. It is the measure of how much hearing a perfect middle ear would restore — the theoretical maximum benefit of surgery.

The gap has a ceiling. A completely disconnected chain or a total middle-ear failure produces a gap of about 50–60 dB; beyond that, sound reaches the cochlea by bone through the skull whatever happens in the middle ear.

Causes

Outer ear: wax, a foreign body, a narrow or absent canal, canal infection with swelling.

Eardrum: perforation, retraction, thickening after infection.

Middle ear: fluid (glue ear, common in children and after colds or flights), infection, otosclerosis fixing the stapes, ossicular erosion or discontinuity, tympanosclerosis, cholesteatoma, rarely a tumour.

Inner ear, disguised: third-window lesions produce an air-bone gap although the middle ear is normal. They are the important exception to the rule that a gap means a mechanical problem.

What it feels like

Muffled hearing, one’s own voice sounding loud or hollow, hearing better on the telephone than across a room, and, in some cases, hearing better in noise. Tinnitus is common. Pain, discharge or fullness point to specific causes.

Treatment principles

Because the inner ear is intact, there are usually several good options and the choice is genuinely personal:

  • Treat the cause where it is reversible: wax, infection, fluid.
  • Observe when the loss is mild and stable.
  • Amplify with a hearing aid — a conductive loss is the easiest kind to aid well — or bypass the problem with a bone-conduction device.
  • Repair or reconstruct with surgery when the mechanics can be restored and the benefit justifies the risk.

The surgical decision framework applies to every one of these choices, and hearing preservation — protecting the healthy inner ear that makes a conductive loss so treatable — runs through all of them.

This page provides general educational information. It cannot replace an individual assessment, which depends on a full history, examination, audiometry and, where relevant, imaging. If you have sudden hearing loss, severe pain, facial weakness, severe dizziness or discharge with fever, seek medical care promptly.