Westermark sign
Pattern seen in radiologic examinations From Wikipedia, the free encyclopedia
In chest radiography, the Westermark sign is a sign that represents a focus of oligemia (hypovolemia) (leading to collapse of vessel) seen distal to a pulmonary embolism (PE).[1] While the chest x-ray is normal in the majority of PE cases,[2] the Westermark sign is seen in 2% of patients.[3]
| Westermark sign | |
|---|---|
| Differential diagnosis | hypovolemia |
Essentially, this is a plain X-ray version of a filling defect as seen on computed tomography pulmonary arteriogram.
The sign results from a combination of:
- the dilation of the pulmonary arteries proximal to the embolus and
- the collapse of the distal vasculature creating the appearance of a sharp cut off on chest radiography.
Sensitivity and specificity
The Westermark sign, like Hampton's hump (a wedge shaped, pleural based consolidation associated with pulmonary infarction), has a low sensitivity (11%) and high specificity (92%) for the diagnosis of pulmonary embolism.[4] Put more simply, the Westermark sign is seldom seen in pulmonary embolism. When visible on a chest X-ray, the Positive Predictive Value is only 33%. That is, 33% of the time that Westermark sign is seen on Chest XRay does a pulmonary embolism actually exist .
Etymology
It is named after Nils Westermark, a Swedish radiologist.[5]
References
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