Westermark sign

Assoc Prof Craig Hacking and Dr Henry Knipe et al.

Westermark sign is a sign of pulmonary embolus seen on chest radiographs. It is one of several described signs of pulmonary embolus on chest radiographs.

The theory behind the sign is either obstruction of the pulmonary artery or distal vasoconstriction in hypoxic lung 3.

In one study (PIOPED) this sign was present on ~10% of chest x-rays of patients with confirmed pulmonary embolus 2

  • focal peripheral hyperlucency secondary to oligemia resulting in a collapsed appearance of vessels distal to the occlusion 2-4
  • central pulmonary vessels may also be dilated 3

The Swedish radiologist Nils Johan Hugo Westermark (1892-1980) 7 first described this sign in 1938 5. Westermark was also an accomplished sailor and won a silver medal, as a member of the Swedish team, at the 1912 Olympics in Stockholm 7.


Article information

rID: 29066
Systems: Chest, Vascular
Section: Signs
Tag: pe
Synonyms or Alternate Spellings:
  • Westermark's sign

Cases and figures

  • Case 1: left-sided
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  • Case 2
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  • Case 3: Westermark and Fleischner signs
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