Pulmonary embolism
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Imaging
Chest radiograph showing hyper-transradiant left upper zone with attenuation of vascular markings.
Multiple large filling defects in the left main pulmonary artery with oligaemic left lung
similar appearances
at a lower level with partly occluded lower lobe pulmonary artery on right
Plain chest radiograph - Signs are non-specific and sensitivity poor. - Can be normal even in patients with life-threatening pulmonary embolism. - Major role is to exclude other diagnoses that might mimic pulmonary embolism. - Helps in interpreting the radionuclide scans - But it can suggest the diagnosis. Acute pulmonary embolism without infarction: - Westermark sign: oligemia of the lung beyond the occluded vessel. - Increase of size of main pulmonary artery ("knuckle sign", "plumping") - Elevation of the hemidiaphragm - Discoid atelectasis (linear or disc-shaped densities) secondary to elevation of hemidiaphragm - hyperventilation - depletion of surfactant - recurrent emboli may cause pulmonary arterial hypertension. Acute pulmonary embolism with infarction: - Gives rise to radiographically detectable consolidation; multifocal in distribution and predominantly in lower lung fields. A "Hampton’s hump" (pleurally based triangular opacity) may rarely be seen. - Infarcts take several months to clear and frequently leave permanent linear scars. - As they resolve, they may melt like an ice cube (cf.acute pneumonia disappears in a patchy fashion). - An air bronchogram is rarely seen. - Cavitation within infarct is rare thin-walled. (Usually secondarily infected or result from septic emboli.) - Pleural effusions common (50%); often bloody. Usually small and unilateral. Spiral CT and ECG-gated MRI: - Infarcts in the lung may be shown as pleural-based wedge-shaped opacities on CT (non-specific). Radionuclide imaging: - Mismatched perfusion defect is the hallmark. - If embolism results in infection matched defects appear: defect of ventilation, corresponding to the perfusion defect. Pulmonary angiography: - Intraluminal filling defect is the hallmark. - Occlusion of a pulmonary artery branch. - Done when - V/Q scan is significantly at variance with the clinical probability of pulmonary embolism - when thrombolytic therapy is contemplated - before embolectomy, vena caval interruption, or filter insertion.