On CT pulmonary angiography (CTPA), a 'saddle embolus' refers to a thrombus at which location?

• A Occlusion of both lower lobe pulmonary arteries bilaterally
• B Thrombus in the left atrium extending into both pulmonary veins
• C Bilateral peripheral segmental pulmonary emboli without central involvement
• D Straddling the main pulmonary artery bifurcation extending into both right and left main pulmonary arteries ✓

Explanation

A saddle embolus is a large thrombus that straddles the main pulmonary artery bifurcation like a saddle, with extensions into both the right and left main pulmonary arteries simultaneously. It is seen on CTPA as a central filling defect bridging the bifurcation. Saddle emboli can cause massive pulmonary embolism with acute right heart strain, obstructive shock, and high mortality. CT findings of right heart strain include right ventricle/left ventricle ratio >0.9, flattening of the interventricular septum (D-sign), and reflux of contrast into the hepatic veins/IVC. Saddle embolus may be an indication for systemic thrombolysis or catheter-directed therapy.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.