What causes Westermark’s sign in lungs on chest x-ray?
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Answer:
Westermark’s sign is caused by focal oligemia distal to an occluded pulmonary artery due to acute pulmonary embolism (PE), appearing on chest x-ray as regional hyperlucency with reduced pulmonary vascular markings.
Why is it called so?
Named after Swedish radiologist Nestor Westermark, who first described it in 1938 as a clarified area of oligemia distal to pulmonary emboli on radiographs.
Pathophysiology
Proximal occlusion of a pulmonary artery by a thromboembolus causes mechanical obstruction of blood flow, leading to distal oligemia (reduced pulmonary blood volume) and focal hyperlucency; reflex hypoxic vasoconstriction may contribute.
Alternative names: None
Other associated named signs: Palla sign (prominent central pulmonary artery), Hampton hump (peripheral wedge-shaped opacity from infarction), Fleischner sign (enlarged main pulmonary artery)
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