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Westermark sign

VascularRadiograph

A focal area of lung oligaemia (increased lucency) distal to an occluded pulmonary artery, sometimes with abrupt vessel cut-off.

What it means

Regional decreased perfusion suggestive of acute pulmonary embolism.

Mechanism

An embolus obstructs a pulmonary artery, reducing perfusion to the distal lung and producing focal hyperlucency.

Associated conditions

  • Acute pulmonary embolism
  • Deep vein thrombosis
  • Right heart strain
  • Pulmonary infarction

Pearls

  • The Westermark sign is specific but insensitive for pulmonary embolism.
  • CT pulmonary angiography remains the definitive test; a Hampton hump suggests infarction.

References

  • Radiopaedia: Westermark sign

For educational use only. This dictionary is a study aid and reference, not a diagnostic tool, and must not be used to guide clinical decisions or patient care. Imaging appearances vary; always correlate with the full clinical picture and confirm with a qualified radiologist.