Skip to content

LESSON 105

Tympanogram types

The Jerger classification sorts tympanograms into types A, As, Ad, B and C by peak pressure and peak height. In this lesson we look at which middle ear conditions each type suggests, and how ear canal volume (ECV) separates effusion, perforation and blockage in a type B tympanogram, with examples.

Watch on YouTube

Follow along

Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will learn the tympanogram types of the Jerger classification and which middle ear conditions each type suggests.
We will also see why ear canal volume is decisive in a type B tympanogram.
The system most widely used to interpret tympanograms is the Jerger classification.
James Jerger published this classification in 1970.
The classification has five basic types: A, As, Ad, B and C.
The classification first looks at the pressure at which the peak occurs.
It then looks at the height of the peak, that is, the peak static admittance.
For curves without a peak, such as type B, ear canal volume completes the interpretation.
The letters describe the shape of the curve; they do not make a diagnosis, they suggest possible middle ear conditions.
A type A tympanogram has a single, clear peak.
The peak is around zero decapascals, within the normal pressure range.
The peak height is also within the normal range for the age group.
This pattern suggests that middle ear pressure and mobility are normal.
But type A does not rule out sensorineural hearing loss; in cochlear losses the tympanogram is usually type A.
If type A is seen in a patient with an air-bone gap, conditions such as otosclerosis should also be considered.
Let us keep the normal type A curve in place for comparison.
In type As the peak is again at normal pressure, but its height is below normal; the s stands for shallow.
Low admittance suggests that the middle ear system has become stiffer.
Otosclerosis, tympanosclerosis or a thickened tympanic membrane can produce this pattern.
A shallow curve that still has a peak can sometimes also be seen as a middle ear effusion begins or resolves.
The boundary between As and normal A depends on the norm range used.
Now let us look at a peak that is much higher than normal.
In type Ad the peak is at normal pressure but clearly higher than normal; the d stands for deep.
High admittance suggests that the system is overly mobile, or flaccid.
Ossicular chain discontinuity can cause this pattern; in that case there is usually also a large air-bone gap.
A thin or flaccid tympanic membrane alone can also cause a type Ad curve.
In this case hearing may be normal, so the curve is always interpreted together with the audiogram.
Type C also has a clear peak, but the peak is shifted to negative pressure.
By Jerger's criterion, the curve is type C if peak pressure is more negative than minus one hundred decapascals; some clinics differ.
Negative peak pressure suggests that middle ear air is being absorbed and the Eustachian tube cannot replace it.
It can be seen in Eustachian tube dysfunction, tympanic membrane retraction, and as an effusion begins or resolves.
Negative pressure may come with a mild conductive loss, especially at low frequencies.
Type C is common in children and can change on its own over time, so follow-up is important.
A type B tympanogram is flat; as pressure changes, no clear admittance peak forms.
In other words, the tympanic membrane seems not to move in response to pressure changes.
Type B has more than one meaning; the same flat curve can be seen in very different conditions.
Sometimes the curve has a very slight rounding; if there is no clear peak, it is still considered type B.
So when we see type B, the first thing to do is look at the ear canal volume.
If the ear canal volume of a type B curve is in the normal range for age, the most likely cause is middle ear fluid, an effusion.
A mass filling the middle ear, such as a cholesteatoma, can produce a similar picture.
If the volume is clearly above normal, the probe tone passes through an opening in the drum and also measures the middle ear space.
This suggests a perforation or an open ventilation tube; in a child with tubes, it shows that the tube is open.
If the volume is clearly below normal, the tip may be blocked or against the wall, or the canal may be full of wax.
In this last case, the first step is to check the probe, repeat the measurement and go back to otoscopy.
In this example, we see a mild conductive loss in a child's right ear.
Air conduction thresholds are between twenty five and thirty five decibels, and bone conduction thresholds are normal.
In the same ear, the tympanogram is type B and the ear canal volume is normal for age.
Together, these findings form a picture consistent with fluid in the middle ear.
In effusion, the air-bone gap usually stays between mild and moderate.
As an effusion resolves, it is common for the tympanogram to change first to type C and then to type A.
Now let us see all the types together; our reference is the normal type A.
In types As and Ad the peak is at normal pressure, but one is low and the other very high.
Type B is flat, while type C shows a peak shifted to negative pressure.
The position of the peak tells us pressure, and its height tells us admittance; in type B, volume completes the picture.
Keeping this image in mind lets you classify a curve on the screen quickly.
In type A, both peak pressure and peak height are normal.
In type As, pressure is normal but the peak is low, which suggests increased stiffness.
In type Ad, pressure is normal but the peak is very high, which suggests excessive mobility.
In type B there is no peak; interpretation is based on ear canal volume.
In type C the peak is at clearly negative pressure, which raises questions about Eustachian tube function.
To classify a curve on the screen we can follow a simple flow: first, we check whether there is a clear peak.
If there is no clear peak, the curve is type B, and we go straight to the ear canal volume.
If there is a peak, we check whether peak pressure is in the normal range; if clearly negative, the curve is type C.
If the pressure is normal, we look at peak height: normal is A, low is As, very high is Ad.
In type C it is useful to note peak height as well; if the peak is also low, this is stated in the report.
In the last step, we interpret the result together with otoscopy and the audiogram.
A common interpretation error in the clinic is to read every flat curve as effusion.
When you see type B, look at the ECV first, then compare the result with otoscopy.
The same flat curve can indicate fluid, a perforation, an open tube, or just a blocked probe.
Assessing the curve, the volume and otoscopy together clearly increases the reliability of the interpretation.
If a type A or As curve comes with an air-bone gap, possible fixation of the ossicular chain is considered.
If a type Ad curve comes with a large air-bone gap, ossicular chain discontinuity comes to mind.
If a type Ad curve comes with normal hearing, the finding is often due to a flaccid or thin tympanic membrane.
Type B with normal volume plus a mild or moderate conductive loss is a picture consistent with effusion.
In every case the final assessment belongs to the physician; our task is to present the findings consistently and completely.
The Jerger classification is a qualitative system based on the shape of the curve.
The boundary between As and A, or between Ad and A, depends on the norm table used.
So today, numerical values such as peak admittance, peak pressure and width are reported along with the letter type.
In infants under six months, a two hundred twenty six hertz tympanogram can look normal even with effusion; one thousand hertz is preferred.
In short, the letter is a good starting point; numerical values and other tests complete the interpretation.
In type A, the peak is at normal pressure and of normal height.
In type As the peak is low, and in type Ad it is very high; in both, pressure is normal.
In type C, the peak is at clearly negative pressure, which raises questions about Eustachian tube function.
Type B is a flat curve; depending on ear canal volume, fluid, perforation or blockage is considered.
Test yourself: the tympanogram is type B and the ear canal volume is very large. What is considered first?
The correct answer is B: a perforation or an open ventilation tube.
The probe tone passes through the opening in the tympanic membrane and also measures the middle ear space, so the volume is large.
In the next lesson we will examine peak admittance, peak pressure, width and volume, with their numerical norms.
Subscribe to the channel so you never miss a new lesson. See you next time!

Keywords

Click a keyword to search all lessons for that term.

Prerequisites

Comments

Questions and comments appear after approval.

No comments yet. Be the first to comment.