Introduction
This topic covers three acute vascular emergencies that a radiologist must recognise quickly: pulmonary embolism, aortic aneurysm (especially when it ruptures) and aortic dissection. For each one the exam answer should give the definition, the main causes, the typical imaging findings, the choice of examination in an emergency, and the complications that change treatment.
Pulmonary embolism
Pulmonary embolism (PE) is blockage of one or more pulmonary arteries, most often by a thrombus that has travelled from deep veins of the legs or pelvis. It is part of venous thromboembolism. Risk factors include immobilisation, recent surgery or trauma, malignancy, pregnancy and the postpartum period, oral contraceptives, previous venous thromboembolism and thrombophilia.
Imaging findings
- CT pulmonary angiography (CTPA) is the first-line test in most patients with suspected PE. It shows a filling defect in a contrast-filled pulmonary artery, sometimes a large central clot at the bifurcation (saddle embolus).
- Signs of right heart strain on CT: right ventricle larger than the left (RV/LV ratio above 1), bowing of the interventricular septum towards the left ventricle, and reflux of contrast into the inferior vena cava and hepatic veins.
- Pulmonary infarction appears as a peripheral, wedge-shaped consolidation, often with a small pleural effusion.
- Chest radiograph is often normal in PE. Possible signs are the Westermark sign (regional oligaemia with a prominent proximal pulmonary artery), the Hampton hump (a peripheral wedge-shaped opacity), an elevated hemidiaphragm and atelectasis. Its main value is excluding other causes of pain and dyspnoea.
- Ventilation-perfusion (V/Q) scintigraphy is the alternative when CT is not possible, for example in contrast allergy or renal failure, and is often preferred in pregnancy. A mismatched segmental perfusion defect with normal ventilation suggests PE.
- Compression ultrasound of the leg veins detects proximal deep vein thrombosis. In an unstable patient, a positive result may be enough to justify treatment without CT. Echocardiography at the bedside shows right ventricular dysfunction.
D-dimer has high sensitivity but low specificity. It is used together with a clinical probability score to exclude PE in low-risk patients, and a positive result requires imaging.