Pulmonary embolism (summary)

This

• this is a basic article which is aimed at article for medical students and non-radiologists in training grades. If you've arrived here by accident, and need
• for more information, head to see the main pulmonary embolism article. article

Pulmonary embolism refers to occlusion of the pulmonary arteries or its branches, usually via venous thrombus.

Clinical presentation

Symptoms of pulmonary embolism include dyspnoea either at rest or on exertion, pleuritic chest pain, cough, orthopnoea and haemoptosis. In addition, if the pulmonary embolism is caused by deep vein thrombosis, symptoms such as calf/thigh pain and swelling may also be present.

On examination, tachypnoea and tachycardia are most commonly noted. Chest findings may be limited, however decreased breath sounds, pleural rub and increased second heart sound may be heard. Cyanosis and decreased oxygen saturation alongside a raised JVP are also associated findings.

Pathology

Obstruction of the pulmonary arteries can be caused by tumour, fat or air. However the most common cause is thrombus arising from the deep venous system of the lower extremities. A thrombus may lodge at the bifurcation of the main pulmonary artery causing haemodynamic compromise, while smaller thrombi may be located more distally.

Pulmonary emoblism is a common complication of deep vein thrombosis, while other risk factors include immobilisation, recent surgery, malignancy, paralysis, smoking and obesity.

Radiographic features

Plain film

Chest x ray is often used to look for alternative causes of the patient's symptoms. Pulmonary embolism findings may include pleural effusion, cardiomegaly and atelectasis. Hampton's hump (shallow wedge shaped opacity in lung periphery) and Westermark's sign (sharp pulmonary vessel with distal hypoperfusion) are rare, but should raise the possibility of pulmonary embolism. However chest x ray can also be normal.

CT

CT pulmonary angiography is used for definitive diagnosis. In pulmonary embolism, filling defects in the branches of the pulmonary artery by contrast enhancement is diagnostic. 

V/Q scans are performed where CT pulmonary angiography is contraindicated such as in severe renal failure, pregnancy or contrast allergy. Pulmonary embolism is shown where areas of lung are ventilated but not perfused.