Eustachian tube dysfunction

Type CReflex: presentDecay: negativeAir–bone gap: None or mild conductive

A peak shifted markedly into negative pressure (type C), reflecting under-aeration of the middle-ear cleft.

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: normalMean air-bone gap: 7 dBAir PTA: 17 dB HLDegree: none

Thresholds within normal limits with no significant air-bone gap.

Often near-normal hearing, or at most a mild low-frequency air-bone gap from the negative middle-ear pressure. The type C tympanogram is usually the more striking abnormality — the audiogram can look almost normal.

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 C is a pressure problem, not necessarily a mobility problem — the peak amplitude can still be normal.

References

  • Jerger J (1970). Clinical experience with impedance audiometry. Archives of Otolaryngology, 92(4), 311–324.
  • Lidén G (1969). The scope and application of current audiometric tests. Journal of Laryngology and Otology, 83(6), 507–520.