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]

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.