Retrocochlear lesion (e.g. vestibular schwannoma)

Type AReflex: elevatedDecay: positiveAir–bone gap: None

A normal type A tympanogram — but with elevated or absent reflexes and POSITIVE reflex decay on the affected side.

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: sensorineuralMean air-bone gap: 0 dBAir PTA: 42 dB HLDegree: moderate

Air and bone thresholds elevated together with no gap — the lesion is cochlear or retrocochlear.

An asymmetric, typically high-frequency sensorineural loss — air and bone thresholds elevated together with NO air-bone gap. The tympanogram is normal; the audiogram and the reflex findings carry the diagnosis. Asymmetry is the feature that prompts retrocochlear work-up.

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

Tympanometry can be entirely normal in retrocochlear disease. Positive (abnormal) reflex decay is the immittance red flag for referral.

References

  • Katz J (Ed.) (2015). Handbook of Clinical Audiology (7th ed.). Wolters Kluwer.
  • Hunter LL, Shahnaz N (2013). Acoustic Immittance Measures: Basic and Advanced Practice. Plural Publishing.
  • Walker JJ, Cleveland LM, Davis JL, Seales JS (2023). Audiogram interpretation. StatPearls. StatPearls Publishing.