Radiological appearance in pulmonary embolism

The plain chest radiograph is better for demonstrating peripheral emboli. The appearances may however be as follows:

• in central emboli - oligaemic lung fields.
• peripheral emboli - linear, or sometimes wedge-shaped, shadows may be seen

The appearances of a pulmonary embolus on a plain chest radiograph are sometimes referred to as Westermark's triad.

Other changes that may occur include an elevated diaphragm, some segmental or lobar volume loss, and small effusions (exudate - usually haemorrhagic). Secondary infection of infarcted lung causes cavitation.

Note that it may be difficult to distinguish pulmonary embolism from infection on a chest radiograph.