This page discusses the diagnosis of pulmonary embolism on various imaging modalities.
CT Angiography
CT angiography is the mainstay modality for suspicion of pulmonary embolism due to wide availability, high diagnostic accuracy, and ability to identify other diagnoses that commonly cause chest pain/dyspnea.
Acute pulmonary embolus manifests as a low attenuation filling defect in the center of a pulmonary artery.
Chronic pulmonary embolus manifests as eccentric/peripheral low attenuation defects, linear webs, or calcified emboli.
Serial axial CT images above show an acute embolus in the anterobasal segmental branch of the right lower lobe pulmonary artery.
VQ Scan
The hallmark of pulmonary embolism on a nuclear medicine lung ventilation/perfusion scan (VQ scan) is a wedge shaped perfusion defect without a corresponding ventilation abnormality.
Right posterior oblique perfusion (top) and ventilation (bottom) showing wedge-shaped defects in a patient with PE
Nonsegmental lesion (prominent hilum, elevated diaphragm, cardiomegaly, etc.) with no other perfusion defects
Nondiagnostic
All other findings
Below is a VQ segmental anatomy reference, adapted from Kamal Singh (NucRadShare) and other references:
VQ Segmental Anatomy Reference
Pulmonary Angiography
Long considered the gold standard for diagnosis of pulmonary embolism, invasive pulmonary angiography is now rarely performed for diagnosis.
Pulmonary embolism is seen as an abrupt cutoff or filling defect within a pulmonary artery after contrast injection, and absence of distal branching vessels. This results in a wedge shaped area of decreased/absent perfusion extending to the lung periphery (similar to a VQ scan).
Anterior view of VQ scan (top) and pulmonary angiogram (bottom)Chronic Thromboembolic Disease – Lateral VQ scan and Pulmonary Angiogram
Signs of PE on Unenhanced Imaging
On chest radiograph the most common findings in pulmonary embolism are a normal chest or nonspecific atelectasis. More specific but less sensitive radiographic findings associated with pulmonary embolus include peripheral round or wedge-shaped opacity (Hampton’s hump), decreased peripheral vascularity (Westermark sign), pleural effusion (usually small with PE), and prominent central artery (Fleischner sign). See Pulmonology Case 4
Unenhanced CT is not adequate for the evaluation of pulmonary embolism. On occasion, however, pulmonary embolus may be seen as as slightly hyperdense pulmonary artery with or without enlargement of the artery.
Noncontrast CT initial (left) and 2 days later (right) with saddle embolus
References
VQ interpretation: Gottschalk A, et al. J Nucl Med 1993;34:1119-1126. Sostman HD, et al. Radiology 1994;193:103-107. Stein PD, et al. Radiographics 2000;20:99-105. Sostman HD, et al. J Nucl Med 2008;1741-1748. Parker JA, et al. SNM Practice Guideline for Lung Scintigraphy 4.0 http://snmmi.files.cms-plus.com/docs/Lung_Scintigraphy_V4_Final.pdf
CTA interpretation: Wittram C, et al. Radiographics 2004;24:1219-1238. Castaner E, et al. Radiographics 2009;29:31-53.
Radiographic findings: Worsley DF, et al. Radiology 1993;189:133-136. Stein PD, et al. Chest 1991;100:598-603.
