Westermark sign

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]

The sign results from a combination of:

1. the dilation of the pulmonary arteries proximal to the embolus and
2. 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] 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.

Name

It is named after Nils Westermark, a Swedish radiologist.^[5]

References

1. Ray J (2003). "Westermark sign and suspected pulmonary embolism.". Can J Cardiol. 19 (3): 317; author reply 317. PMID 12680403.
2. Introduction to Chest Radiography. http://www.med-ed.virginia.edu/courses/rad/cxr/index.html
3. 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.
4. 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.
5. Dorland's Illustrated Medical Dictionary (32 ed.). Elsevier Health Sciences. 2011-06-09. p. 2080. ISBN 1455709859.