Westermark sign

Last revised by Craig Hacking on 3 Jun 2020

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.

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