CTICasesLeft Atrial Contrast Mixing Artifact
Imaging findings
Chest CT angiography in a patient with squamous cell carcinoma causing right lower lobe collapse shows a prominent contrast filling defect in the left atrium, projecting from the right inferior pulmonary vein. The ROI reveals high attenuation, and there is no true thrombus, representing slow flow from the collapsed lung segment.
Key takeaways
Contrast mixing artifact (or contrast smoke) in the left atrium is a common pitfall on CT angiography. It occurs when unopacified blood from a vein drains into the atrium and mixes poorly with contrast-opacified blood. This is particularly pronounced in collapsed or consolidated lung segments where blood flow is sluggish, simulating a left atrial thrombus or tumor.
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