CTICasesFontan Physiology (Contrast Mixing and Streaming Artifacts)
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Imaging findings
Contrast-enhanced chest CT in a 22-year-old with repaired complex congenital heart disease (single ventricle, single atrium, transposition of the great arteries, and an extracardiac Fontan conduit) shows intense contrast layering and "streaming" artifacts within the pulmonary arteries, creating pseudo-filling defects that mimic pulmonary embolism. Associated mosaic lung attenuation is present due to regional vascular over-perfusion.
Key takeaways
Patients with Fontan physiology rely on passive systemic venous pressure to perfuse the lungs, resulting in slow, non-turbulent blood flow that produces prominent contrast streaming and layering artifacts on CT. This can easily be mistaken for acute pulmonary embolism; recognition of the post-operative congenital anatomy and the unmixed nature of the contrast is crucial to avoid a false-positive diagnosis.
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