Ossicular chain discontinuity

Type AdReflex: absentDecay: n/aAir–bone gap: Conductive, often large (>30 dB)

An abnormally deep (type Ad) peak from a hypermobile system, classically with a large conductive air–bone gap.

Audiogram & tympanogram

Audiogram

0204060801001202505001k2k4k8kFrequency (Hz)Hearing level (dB HL)[[[[[[○ air conduction[ bone conduction

Tympanogram

-400-300-200-10001002000.00.51.01.52.02.53.0Ear-canal pressure (daPa)Admittance (mmho)

Reading the two together

Loss type: conductiveMean air-bone gap: 47 dBAir PTA: 55 dB HLDegree: moderate

An air-bone gap with normal bone thresholds — the lesion is in the outer or middle ear.

A large, often downsloping conductive loss with a wide air-bone gap — frequently the maximal conductive loss the ear can show (around 60 dB). Bone thresholds remain normal. Contrast the downslope here with the upslope of otosclerosis.

The audiogram tells you how much hearing is lost and where the lesion sits (conductive vs sensorineural); the tympanogram tells you what the middle ear is doing mechanically. Read as a pair, they pin down the diagnosis far more tightly than either does alone.

Teaching point

Type Ad signals hypermobility — discontinuity or a flaccid/monomeric drum. Pair it with audiometry to separate the two.

References

  • Jerger J (1970). Clinical experience with impedance audiometry. Archives of Otolaryngology, 92(4), 311–324.
  • Hunter LL, Shahnaz N (2013). Acoustic Immittance Measures: Basic and Advanced Practice. Plural Publishing.