An abnormal tympanogram does not provide a diagnosis: the patient may have acute otitis media (AOM), middle ear with effusion or a hole in the eardrumTympanometry in the Diagnosis of Acute Otitis.
Technique
The tympanogram of a child that resists the examination is rarely reliable. The child may participate in the examination by pressing the tympanometer button him/herself, whereby the examination often may be carried out in good collaboration.It is best to perform tympanometry before cleaning the ear canal.
The tympanometer ear probe with a soft plastic tip is inserted tightly into external auditory meatus.
A seal can be created by lightly pulling the earlobe backwards whilst gently rotating the probe into a position where it can obtain a ”direct view” of the tympanic membrane.
When an airtight seal has been created the automatic recording device will be triggered. A measurement typically lasts for 1-2 seconds.
Interpretation
Interpretation should only be attempted if the curve is unbroken and continuous. Repeated measurements that yield identical results increase reliability. Regular practice will help the examiner to obtain reliable and interpretable curves.
The most important thing to note when interpreting a tympanogram is the shape of the curve, not the height of the peak or its position on the pressure axis (X axis; picture 2).
The sharper the peak, the lower the probability that middle ear effusion is present.
A more rounded but still a definite peak is a common finding in the absence of middle ear effusion.
The flatter and lower the curve, the higher the probability that middle ear effusion is present.
The elasticity of the child's ear canal may ”echo” back and produce very low curves, even totally flat lines.
Tympanograms are categorised into types A, C and B according to the position of the peak of the curve on the pressure axis (X axis).
Type A graph (-200 - +30 dPa), a sharp peak which falls along the reference range (picture 1): middle ear effusion very unlikely
Type C graph, the peak is displaced to the left (< -200 dPa; picture 3): middle ear effusion unlikely; negative pressure within the middle ear, which is normal during a common cold
Type B graph, a flat line, no identifiable peak (picture 4): middle ear effusion likely, particularly if the result is obtained with repeated measurements
A tympanostomy tube or a perforation in the tympanic membrane may lead to instrument-specific interpretation errors: some instruments fail to plot any graph whilst others will plot a type B graph. The operator must familiarise himself/herself with the instrument being used.
References
Smith CG, Paradise JL, Sabo DL, Rockette HE, Kurs-Lasky M, Bernard BS, Colborn DK. Tympanometric findings and the probability of middle-ear effusion in 3686 infants and young children. Pediatrics 2006 Jul;118(1):1-13. [PubMed]
Koivunen P, Alho OP, Uhari M, Niemelä M, Luotonen J. Minitympanometry in detecting middle ear fluid. J Pediatr 1997 Sep;131(3):419-22. [PubMed]
Helenius KK, Laine MK, Tähtinen PA et al. Tympanometry in discrimination of otoscopic diagnoses in young ambulatory children. Pediatr Infect Dis J 2012;31(10):1003-6. [PubMed]