Westermark sign
| Westermark sign | |
|---|---|
| Differential diagnosis | hypovolemia |
In
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]
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 proximalto 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
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 [1]
.
Etymology
It is named after Nils Westermark, a Swedish radiologist.[5]
References
- PMID 12680403.
- ^ Introduction to Chest Radiography. http://www.med-ed.virginia.edu/courses/rad/cxr/index.html
- PMID 8372182.
- ^ Gurney J. CT: Diagnosis of Pulmonary Embolism. chestx-ray.com. Available at: http://www.chestx-ray.com/Lectures/PulmEmbLecture/PulmEmbolus.pdf. Accessed on: November 13, 2006.
- ISBN 978-1455709854.