[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [ENT](https://durgical.com/en/ent/) › [The ENT examination](https://durgical.com/en/ent/areas/exam/) › Tympanometry and the acoustic reflex # 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. Updated Nov 5, 2026 ## Key points - Type A: peak near 0 daPa with normal height: normal middle ear (a sensorineural loss is still possible). - Type B (flat): effusion if canal volume is normal; perforation or a patent tube if volume is large; wax or a blocked probe if it is small. - Type C: peak at negative pressure: eustachian tube dysfunction or an early or resolving effusion. - As (shallow) means a stiff system such as otosclerosis or tympanosclerosis; Ad (very tall) means a floppy system such as ossicular discontinuity. - The acoustic reflex is lost with any conductive loss, with facial paralysis and with lesions of the auditory nerve. ## 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. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/ent/tympanometry-and-the-acoustic-reflex/) ## Connections ## Related 1 - [Pure-tone audiometry: how to read an audiogram](https://durgical.com/en/ent/pure-tone-audiometry-how-to-read-an-audiogram/) ## Related conditions 1 - [Otitis media with effusion and chronic suppurative otitis media](https://durgical.com/en/conditions/otitis-media-with-effusion-and-chronic-suppurative-otitis-media/) [← All of ENT](https://durgical.com/en/ent/) 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](https://www.msdmanuals.com/professional/ear-nose-and-throat-disorders/hearing-loss/hearing-loss) (MSD Manual Professional Edition, 2026); [Otitis Media (Serous)](https://www.msdmanuals.com/professional/ear-nose-and-throat-disorders/middle-ear-and-tympanic-membrane-disorders/otitis-media-serous) (MSD Manual Professional Edition, 2026); [Ear Infections in Children](https://www.nidcd.nih.gov/health/ear-infections-children) (NIDCD, National Institutes of Health, 2022); [Otitis Media (Chronic Suppurative)](https://www.msdmanuals.com/professional/ear-nose-and-throat-disorders/middle-ear-and-tympanic-membrane-disorders/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. --- Source: https://durgical.com/en/ent/tympanometry-and-the-acoustic-reflex/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/ent/tympanometry-and-the-acoustic-reflex/