Pulmonary embolism (summary)

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This is a basic article for medical students and other non-radiologists

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

Reference article

This is a summary article; read more in our article on pulmonary embolism.

Summary

  • epidemiology
    • incidence is 0.5-1.0 per 1000
    • increased incidence with cancer or immobility
    • in the under 55s, commoner in females
  • presentation
    • dyspnea either at rest or on exertion
    • pleuritic chest pain, cough, orthopnea and hemoptysis
    • if caused by deep vein thrombosis, calf/thigh pain and swelling may occur
  • pathophysiology
    • obstruction of the arteries can be caused by tumor, fat or air
    • the most common cause is thrombus arising from the deep venous system of the lower extremities
    • thrombus may lodge at the bifurcation of the main pulmonary artery causing hemodynamic compromise, while smaller thrombi may be located more distally
    • it is a common complication of deep vein thrombosis
    • other risk factors include immobilization, recent surgery, malignancy, paralysis, smoking and obesity
  • investigation
    • clinical scores are helpful to determine who requires investigation
    • D-dimers can be useful in low-risk patients to rule out a VTE
    • visualizing the clot using CTPA is the commonest way to make the diagnosis although nuclear medicine studies can be used to make the diagnosis too
  • treatment
    • initially, resuscitation with oxygen and supportive therapy
    • anticoagulation therapy is then administered depending on the risk of bleeding
    • alternative treatment includes thrombolysis, embolectomy and inferior vena cava filters
    • early diagnosis and anticoagulation are critical in pulmonary embolism

Radiographic features

X-ray

Chest radiographs are often performed to look for alternative causes for symptoms. They are usually either normal or show nonspecific findings which include pleural effusion, cardiomegaly and atelectasis. More specific findings are rare but include Hampton hump (shallow wedge-shaped opacity in lung periphery) and Westermark sign (sharp pulmonary vessel with distal hypoperfusion).

CT

CT pulmonary angiography is used for definitive diagnosis. A CTPA requires the use of iodinated contrast and appropriate assessment of renal function and questioning about the history of diabetes etc. is required.

Pulmonary emboli cause filling defects in the branches of the pulmonary arterial system. If there is a central filling defect that spans the main pulmonary artery where it branches into the left and right pulmonary arteries, it is called a saddle embolus. Emboli may completely obstruct the vessel or be partially obstructive.

Ventilation/perfusion scan

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 the lung are ventilated but not perfused.

Pulmonary angiography

The historical gold standard for diagnosis of pulmonary embolism, it is reserved for patients where CT pulmonary angiography or V/Q scans are non-diagnostic. A filling defect or vessel occlusion is diagnostic of pulmonary embolism.

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