What Does a Flat Line in Tympanometry Mean?

21 August 2025

A tympanometry test is an essential diagnostic tool when evaluating middle ear function. It measures the compliance of the middle ear systems, specifically, how well the tympanic membrane(eardrum) responds to changes in air pressure.

One of the most telling results you might encounter is a flat line on the tympanogram, often referred to as a Type B tympanogram. While it may look simple at first glance, this pattern can reveal much about what’s happening behind the eardrum.

In this blog, we’ll cover:

What a flat tympanogram indicates
Common causes behind a flat tympanogram
How ear canal volume measurements assist in diagnosis
What a flat tympanogram means for patient care

What Does a Flat Line on a Tympanogram Mean?

When pressure is applied in the ear canal, a flat tympanogram indicates little or no eardrum movement. In normal conditions, the tiny bones in the middle ear (the ossicles) and the tympanic membrane work together to transmit sound and maintain pressure balance.

During a tympanometry test, the device alters air pressure in the ear canal and measures the reflected sound energy. In healthy ears, this generates a clear peak on the graph, corresponding to maximum mobility. This is called a Type A tympanogram, showing normal functionality of the middle ear system.

In contrast, when the tympanic membrane does not move, the tracing appears flat, showing no peak. This suggests a serious disruption in middle ear function.

In simple terms: A flat line on a tympanogram means the eardrum isn’t moving properly—and that could be due to fluid in the middle ear, a perforated eardrum, or blockage in the ear canal.

Type B (flat) Tympanogram

What Causes a Flat Tympanogram?

Several clinical conditions can result in a flat tympanogram. Each affects the compliance of the middle ear in different ways:

1. Fluid in the Middle Ear (Otitis Media with Effusion)
This is the most common cause of a flat tracing, especially in children. Fluid buildup behind the eardrum reduces mobility, preventing normal movement in response to changes in air pressure. Even without an active ear infection, lingering fluid can persist and affect hearing.

2. Perforated Tympanic Membrane
During the test, a hole or tear in the eardrum prevents pressure from building in the canal. Without a proper seal, the tympanometer cannot measure middle ear function, resulting in a flat line.

3. Pressure Equalization Tube (PE)
If a PE tube is present and functioning (i.e., it’s open), pressure from the canal will not change inside the middle ear. Again, this creates a flat tympanogram.

4. Eustachian Tube Dysfunction
The eustachian tube connects the middle ear to the throat and helps regulate air pressure. If it’s blocked or not functioning correctly, it can cause negative pressure in the middle ear. Over time, this may lead to fluid buildup, retraction of the eardrum, or even a flat tracing if the condition is chronic.

5. Impacted Cerumen or Probe Blockage
Sometimes a flat tracing isn’t caused by a middle ear problem at all—it’s simply a blockage. This can happen if the ear canal is full of wax, if wax or debris clogs one of the probe’s openings, or if the probe tip is pressed against the ear canal wall. It can also occur if a wire or tube becomes disconnected.

6. Abnormal Growth in the Middle Ear
A cholesteatoma is noncancerous growth of skin cells that forms in the middle ear, often as a result of chronic ear infections or eustachian tube dysfunction. As it enlarges, it can erode bone, damage the ossicles, or press against the eardrum, restricting its movement.

This reduced mobility can produce a flat tympanogram, either with a normal ear canal volume if the eardrum is intact, or with a large volume if the cholesteatoma has caused a perforation. Early detection is important, as untreated cholesteatomas can lead to hearing loss and other complications.

Diagnosing the Underlying Cause – The Role of Ear Canal Volume

To determine why a tympanogram shows a flat line, clinicians must consider ear canal volume(ECV). Tympanometers measure this volume during the test, and the result is a key diagnostic clue.

Let’s look at how ECV values relate to the possible causes:

Clinical Interpretation:

Flat line + normal ECV = likely middle ear effusion
Flat line + large ECV = suspect ear drum perforation
Flat line + small ECV = consider probe placement or cerumen

This ECV reading adds a critical layer of insight to the tympanogram result, helping clinicians understand what’s happening inside the ear—even when the patient cannot describe their symptoms clearly.

Clinical Implications

Flat tympanograms are often linked to conductive hearing losses caused by issues in the middle ear system. In many cases, these are temporary, as with fluid or infections, but they can also indicate more serious or chronic conditions, especially when related to eustachian tube dysfunction or repeated ear infections.

It’s essential to assess tympanometry results alongside:

Otoscopic exam findings: a video otoscope can help to see the tympanic membrane clearly along with fluid in the middle ear space.
Patient history (recent infections, PE tubes, trauma)
Pure tone audiometry and speech testing results

This comprehensive approach ensures accurate diagnosis and better patient outcomes.

A flat line on a tympanogram isn’t a diagnosis by itself but a powerful clue. With careful interpretation of ear canal volume, clinical history, and otoscopy, you can determine whether the cause is fluid in the middle ear, a perforated eardrum, eustachian tube dysfunction, or something more benign like wax impaction.

Understanding how to interpret these results empowers clinicians to take the next step—whether that’s medical referral, further audiologic testing, or patient counseling.

View All

What Does a Flat Line in Tympanometry Mean?

What Does a Flat Line on a Tympanogram Mean?

What Causes a Flat Tympanogram?

Diagnosing the Underlying Cause – The Role of Ear Canal Volume

Clinical Implications

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