Westermark sign

Westermark sign
Differential diagnosishypovolemia

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.

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:

  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.
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