Pulmonary embolism

Pulmonary embolism (PE) occurs when thrombus, most often from a deep vein thrombosis, lodges in the pulmonary arterial tree. Risk factors include immobility, surgery, cancer, pregnancy, oestrogen therapy and inherited thrombophilia.

Clinical presentation

Breathlessness, pleuritic chest pain, haemoptysis, tachycardia, hypoxia or collapse. Clinical probability scores (Wells, Geneva) combined with D-dimer decide who needs imaging.

Radiographic features

CT pulmonary angiography

• Filling defects within contrast-opacified pulmonary arteries
• A saddle embolus straddles the bifurcation of the main pulmonary artery
• Right heart strain: right ventricle larger than the left, septal bowing, reflux of contrast into the IVC
• Peripheral wedge-shaped infarcts

Chest radiograph

Often normal; it is mainly used to exclude other causes. Rare signs include Hampton hump and Westermark sign.

V/Q scintigraphy

An alternative when contrast is contraindicated and in pregnancy.

Treatment and prognosis

Anticoagulation for most patients. Thrombolysis is reserved for high-risk PE with haemodynamic instability; catheter-directed or surgical options exist for selected cases.

Practical points

Poor contrast timing and breathing artefact can mimic emboli. Check that filling defects are seen on more than one slice and plane.