Tympanogram Interpretation for GP Registrars

Tympanometry tests middle ear function by measuring how compliant the eardrum is at different ear canal pressures.
A tympanogram plots the compliance (or admittance) of the ear drum across a range of ear canal pressures. Tympanometry can also estimate the Ear Canal Volume (ECV), which can be normal (0.5 – 1.5 mL in children, 0.5 – 2 mL in adults), low due to impacted wax, or high due to a perforation.
A normal tympanogram has a peak of maximal compliance between +/- 100 daPa, which represents the point where pressure in the middle ear equals pressure in the external canal.
Tympanograms can be described as Type A, B or C. Type A has a peak between +/- 100 daPa, Type B is flat, and Type C is shifted to the left. There are also subtypes for peaks that are too tall or to short.

Common Patterns

  • A normal ear will have a Type A tympanogram

  • Normal Type A tympanogram. There is a peak between +/-100 daPa and the height of the peak (peak compliance) is between 0.3-1.5 mL. The Ear Canal Volume is normal (0.5-1.5 mL for a child, or 0.5-2 mL for an adult).

    Type AD subtype. The height of the peak is >1.5 mL, which suggests the tympanic membrane is highly compliant (ie disarticulation / subluxation of ossicles, overly mobile TM, or healed TM over previous perforation).

    Type AS subtype. The height of the peak is <0.3 mL, which suggests less compliance. This could be due to some fluid in the middle ear, or otosclerosis / tympanosclerosis.

  • A Type B tympanogram suggests middle ear pathology.

  • Type B. The tympanogram is flat. This can suggest a middle ear effusion, or tympanosclerosis / cholesteatoma / tumour. Note that pneumatic otoscopy is more sensitive and specific for a middle ear effusion.

    Type B + high ear canal volume (>1.5 mL in kids, or >2 mL in adults). This suggests there is a perforation (or a functioning grommet) as the external canal is freely communicating with the middle ear and eustachian tube.

    Type B + low ear canal volume (< 0.5 mL). This suggests the external ear canal is full of wax, or the tympanometry probe wasn't placed properly so the tip was flat up against the wall of the ear canal.
  • A Type C tympanogram suggests negative pressure in the middle ear.

  • Type C tympanogram. There is a peak but it is shifted to the left of normal. This suggests there is negative pressure in the middle ear, such as sinusitis or eustachian tube dysfunction without a middle ear effusion.

    Type CD subtype. This suggests there is negative pressure in the middle ear as well as a highly compliant tympanic membrane (ie healed perforation or ossicular subluxation).

    Type CS. This suggests there is negative pressure in the middle ear as well as reduced compliance, which could be from eustachian tube dysfunction with some fluid in the middle ear.

    Video

    Exercise: Can you identify these patterns?

    Normal Type A tympanogram. There is a peak between +/-100 daPa and the height of the peak (peak compliance) is between 0.3-1.5 mL. The Ear Canal Volume is normal (0.5-1.5 mL for a child, or 0.5-2 mL for an adult).
    Type AD subtype. The height of the peak is >1.5 mL, which suggests the tympanic membrane is highly compliant (ie disarticulation / subluxation of ossicles, overly mobile TM, or healed TM over previous perforation).
    Type AS subtype. The height of the peak is <0.3 mL, which suggests less compliance. This could be due to some fluid in the middle ear, or otosclerosis / tympanosclerosis.
    Type B. The tympanogram is flat. This can suggest a middle ear effusion, or tympanosclerosis / cholesteatoma / tumour.
    Type B + high ear canal volume (>1.5 mL in kids, or >2 mL in adults). This suggests there is a perforation (or a functioning grommet) as the external canal is freely communicating with the middle ear and eustachian tube.
    Type B + low ear canal volume (< 0.5 mL). This suggests the external ear canal is full of wax, or the tympanometry probe wasn't placed properly so the tip was flat up against the wall of the ear canal.
    Type C tympanogram. There is a peak but it is shifted to the left of normal. This suggests there is negative pressure in the middle ear, such as sinusitis or eustachian tube dysfunction without a middle ear effusion.
    Type CD subtype. This suggests there is negative pressure in the middle ear as well as a highly compliant tympanic membrane (ie healed perforation or ossicular subluxation).
    Type CS. This suggests there is negative pressure in the middle ear as well as reduced compliance, which could be from eustachian tube dysfunction with some fluid in the middle ear.
    Otosclerosis. Note the Carhart notch at 2000Hz.

    Exercise: Which of the following are true?

    • A flat tympanogram suggests a perforation.
      A flat tympanogram (type B) suggests a middle ear effusion, or tympanosclerosis / cholesteatoma / tumour.
    • Impacted earwax can cause a low ECV.
      Yes, a very low calculated Ear Canal Volume (ECV) suggests the external ear canal is either full of wax, or the tympanometry probe was placed flat against the wall of the ear canal by mistake.
    • The Type A tympanogram is always normal.
      No, there are subtypes of Type A that are abnormal, ie Type AD could result from a recently healed perforation, or Type AS could be otosclerosis.
    • Otitis media with effusion = type B tympanogram.
      Yes, a middle ear effusion can causes a Type B tympanogram. Note that pneumatic otoscopy is more sensitive and specific for a middle ear effusion.
    • Eustachian tube dysfunction = type B tympanogram.
      No, eustachian tube dysfunction will cause a type C tympanogram, due to the negative pressure in the middle ear.
    • An ECV of 3 mL is normal.
      No, the Ear Canal Volume (ECV) should be 0.5-1.5 mL in kids, or 0.5-2 mL in adults. A larger ECV suggests a perforation or functioning grommet as the external canal is freely communicating with the middle ear and eustachian tube.
    • Peak compliance of 0.3 – 1.5 mL is normal.
      Yes, the range of peak tympanic membrane compliance (the height of the peak on the tympanogram) is generally 0.3-1.5 mL.
    • A left shifted peak = increased pressure in the middle ear.
      No, a left shifted peak (type C tympanogram) = negative pressure in the middle ear. If there is increased pressure in the middle ear (ie a bulging TM), it is possible for the peak to shift to the right.
    • Grommets do not affect the tympanogram if patent.
      No, grommets can cause a flat (type B) tympanogram and if they are patent there will be a high Ear Canal Volume (ECV).