The 'Westermark sign' on chest X-ray in pulmonary embolism refers to:

• A Focal oligaemia — relative hyperlucency of the lung distal to an occluded pulmonary artery ✓
• B Wedge-shaped peripheral pleural-based opacity (Hampton's hump) representing pulmonary infarction
• C Dilatation of the descending right pulmonary artery (Palla's sign)
• D Abrupt cut-off of the pulmonary artery on frontal chest X-ray

Explanation

The Westermark sign in pulmonary embolism is focal oligaemia — reduced or absent vascular markings in the lung segment or lobe distal to an occluded pulmonary artery, creating relative radiolucency compared to adjacent lung. This reflects the absence of blood flow beyond the embolus. Hampton's hump (option B) is the peripheral pleural-based triangular or wedge-shaped consolidation from pulmonary infarction. Palla's sign refers to enlargement of the right descending pulmonary artery. All three are classic CXR signs of PE, but all have low sensitivity (~5–30%); CT pulmonary angiography is definitive.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.