Tympanometry and the acoustic reflex
- Examination
Tympanometry measures how easily the eardrum moves as air pressure changes; it shows fluid, perforation and eustachian tube problems without the patient's help.
What it is
Tympanometry is an objective test of the middle ear. A probe that seals the ear canal changes the air pressure and records how much sound the eardrum admits (its compliance). A healthy middle ear moves best at atmospheric pressure, producing a peak near 0 daPa. Fluid, negative pressure, a stiff or a broken ossicular chain and a perforation each change the curve in a typical way, classified as types A, As, Ad, B and C. The acoustic reflex, measured with the same probe, records the stapedius muscle contracting to loud sound. Both are read together with otoscopy and the audiogram.
Findings and interpretation
- A flat curve is not always fluid: always look at the canal volume before calling it an effusion.
- In a child with a flat tympanogram and normal volume, middle-ear effusion is the usual cause, often after an acute otitis media.
- A negative-pressure peak with a retracted drum fits eustachian tube dysfunction.
- Otosclerosis gives a normal or reduced (shallow) peak, so a conductive loss with a near-normal tympanogram and normal drum suggests it.
- A very tall peak with a conductive loss suggests ossicular discontinuity, for example after trauma.
- An absent acoustic reflex with a normal tympanogram and asymmetric sensorineural loss raises suspicion of a retrocochlear lesion.
How it is done
- Do otoscopy first: the canal must be clear of wax and debris.
- Choose a probe tip that seals the canal; the patient sits still and does not talk or swallow during the test.
- The device sweeps the canal pressure from positive to negative (about +200 to −400 daPa) and records compliance.
- Read three values: ear canal volume, the pressure of the peak and the height of the peak.
- Acoustic reflex: loud tones are presented and the stapedius contraction is recorded in the same and the opposite ear.
- Interpret together with otoscopy and the audiogram, never alone.
Tympanogram types
| Type | Shape | Usual meaning |
|---|---|---|
| A | Peak near 0 daPa, normal height | Normal middle ear |
| As | Normal pressure, low peak | Stiff system: otosclerosis, tympanosclerosis |
| Ad | Normal pressure, very tall peak | Ossicular discontinuity, flaccid segment of the drum |
| B, normal volume | Flat | Middle-ear effusion |
| B, large volume | Flat | Perforation or patent ventilation tube |
| C | Peak at negative pressure | Eustachian tube dysfunction, early or resolving effusion |
Common mistakes
- Taking a type A tympanogram as normal hearing: sensorineural loss and some ossicular fixations give type A.
- Calling a flat trace with a large volume an effusion: it means a hole in the drum or an open tube.
- Testing over wax: the result is a small volume and a flat curve that says nothing about the middle ear.
Next step / Initial management
- Flat curve with normal volume in a child: hearing test and recheck, since many effusions clear; refer to ENT (routine) if it persists for months or causes hearing loss or speech delay.
- Adult with a one-sided flat curve lasting more than 8 weeks: refer to ENT for nasopharyngeal endoscopy to exclude a tumour.
- Flat curve with large volume: confirms a perforation; keep the ear dry and refer routinely to assess repair.
- Absent reflexes with a normal middle ear and asymmetric sensorineural loss: priority referral for MRI of the internal auditory canals.
Test yourself
Think of the answer, then tap the question to see it.
A 4-year-old with hearing difficulty has a flat tympanogram with normal canal volume. What is most likely behind the drum?
Middle-ear effusion (otitis media with effusion).
A flat tympanogram shows a very large canal volume. What does that suggest?
A perforated eardrum or a patent ventilation tube: the probe is measuring the middle ear space as well.
Which tympanogram type fits eustachian tube dysfunction?
Type C: the peak is at negative pressure.
Why does an absent acoustic reflex not locate the lesion by itself?
It disappears with any conductive loss, with facial paralysis and with auditory nerve lesions; the tympanogram and audiogram tell which.
Connections
Educational content; it does not replace a medical assessment and is not a clinical instruction. For a real case, follow current guidelines and specialist advice.
Sources: Hearing Loss (MSD Manual Professional Edition, 2026); Otitis Media (Serous) (MSD Manual Professional Edition, 2026); Ear Infections in Children (NIDCD, National Institutes of Health, 2022); Otitis Media (Chronic Suppurative) (MSD Manual Professional Edition, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.