The theory behind the sign is either obstruction of the pulmonary artery or distal vasoconstriction in hypoxic lung .
In one study (PIOPED) this sign was present on ~10% of chest x-rays of patients with confirmed pulmonary embolus .
- focal peripheral hyperlucency secondary to oligemia resulting in a collapsed appearance of vessels distal to the occlusion
- central pulmonary vessels may also be dilated
History and etymology
The Swedish radiologist Nils Johan Hugo Westermark (1892-1980) first described this sign in 1938 . Westermark was also an accomplished sailor and won a silver medal, as a member of the Swedish team, at the 1912 Olympics in Stockholm .