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Saddle Pulmonary Embolus

Key: Ao - thoracic aorta. MPA - main pulmonary artery. svc - superior vena cava. arrow - pulmonary embolus.
Prevalence: Unsuspected 1.5% - highest in patients with cancer2, 1% in all hospitalised patients1. Third leading cardiovascular cause of death3.
Aetiology: Thrombotic – >90% of thrombotic PE is associated with DVT, right atrial neoplasia, thrombogenic IV catheters, endocarditis of tricuspid valve1.
Non thrombotic – septic, fat, tumour, amniotic fluid, foreign material (cement, talc, mercury, air)2.
Presentation: Acute – Variable, classic triad of haemoptysis, pleural friction rub and thrombophlebitis <33%, also, dyspnoea, chest pain, cough, syncope.
Chronic – Non specific, emboli occur, organise, recanalise with stenosis leading to pulmonary hypertension1.
Radiology: CECT – Filling defect, contrast tracking around thrombus or complete occlusion. 90% sensitivity and specificity for main, lobar and segmental vessels. Lower for subsegmental vessels3.
Alternatives – V/Q scan (low clinical + low scan probability = 4% prevalence of PE, high clinical + high scan probability = 96% prevalence of PE, however, large group of intermediate probabilities will require additional testing)3, pulmonary angiography (>95% sensitive and specific but 0.2-0.5% mortality rate and significant morbidity)1.
Management: Anticoagulation – heparin, warfarin. Thrombolysis – urokinase.
Complications: Death, pulmonary infarction, chronic pulmonary artery hypertension.
References:
1. Dahnert W. Radiology Review Manual 5th Ed Lippincott Williams and Wilkins
2. Daehee H, et al. Thrombotic and Nonthrombotic Pulmonary Arterial Embolism: Spectrum of Imaging Findings. RadioGraphics 2003; 23: 1521
3. LR Goodman. CT of acute pulmonary emboli: where does it fit? RadioGraphics 1997; 17: 1037.
Credit: Dr Neha Singh
http://www.radpod.org

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