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). While the chest x-ray is normal in the majority of PE cases, the Westermark sign is seen in 2% of patients.
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. This means that the sign is only present in 11% of pulmonary emboli, and absence of the sign is present 92% of the time that there is no embolus. Put more simply, it is not often seen in PE, but if it is seen, it is very likely PE.
- Ray J (2003). "Westermark sign and suspected pulmonary embolism.". Can J Cardiol. 19 (3): 317; author reply 317. PMID 12680403.
- Introduction to Chest Radiography. http://www.med-ed.virginia.edu/courses/rad/cxr/index.html
- Worsley D, Alavi A, Aronchick J, Chen J, Greenspan R, Ravin C (1993). "Chest radiographic findings in patients with acute pulmonary embolism: observations from the PIOPED Study.". Radiology. 189 (1): 133–6. doi:10.1148/radiology.189.1.8372182. 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.
- Dorland's Illustrated Medical Dictionary (32 ed.). Elsevier Health Sciences. 2011-06-09. p. 2080. ISBN 1455709859.
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