A chest CT pulmonary angiogram (CTPA) in a 50-year-old with acute dyspnoea shows a filling defect that straddles the bifurcation of the main pulmonary artery. What is this finding called and what is its immediate haemodynamic implication?
- A Westermark sign; indicates reduced perfusion distal to the clot
- B Saddle embolus; causes obstructive shock by outflow obstruction of both main pulmonary arteries ✓
- C Hampton hump; indicates pulmonary infarction
- D Fleischner sign; indicates central pulmonary arterial dilatation
Correct answer: B. Saddle embolus; causes obstructive shock by outflow obstruction of both main pulmonary arteries
Explanation
A saddle embolus straddles the main pulmonary artery bifurcation, obstructing outflow into both main pulmonary arteries simultaneously, causing acute outflow obstruction and obstructive shock with right heart strain. Westermark sign is oligaemia distal to a clot on plain X-ray. Hampton hump is a wedge-shaped pleural-based opacity from infarction. Fleischner sign refers to prominent pulmonary artery on plain film.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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