What causes the floating viscera sign on aortography?
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Answer:
The floating viscera sign describes abdominal visceral branch vessels, typically the coeliac axis, superior mesenteric artery and renal arteries, opacifying normally while the aortic true lumen from which they arise shows little or no contrast, so the organs appear to float free of any visible aortic supply. It is seen on catheter angiography and on CT angiography in aortic dissection, and signifies dynamic compromise of the true lumen: a pressurised false lumen compresses the true lumen upstream, restricting antegrade flow and contrast delivery, even though the true lumen calibre at the level of the branch vessels themselves looks adequate. The sign is prognostically important because it identifies critical haemodynamic compromise of the true lumen and a risk of visceral malperfusion, and it warns the interventionalist that contrast injected into the true lumen will not reflect the true perfusion state of the abdominal organs.
Why is it called so?
The abdominal organs opacify while the aorta feeding them does not, so on the image the viscera appear to float unattached to any vessel.
Pathophysiology
In dissection the false lumen is often larger and at higher pressure than the true lumen. Upstream compression of the true lumen by the mobile intimal flap reduces antegrade flow, so contrast injected proximally is diverted or delayed and the true lumen fills poorly. Distally, branch vessels may still receive perfusion, either from the true lumen through the compressed segment or through fenestrations, so the organs opacify. The mismatch between poorly opacified aorta and well-opacified viscera produces the sign, and it reflects dynamic rather than static obstruction, which is why the true lumen calibre near the branches can look deceptively normal.
Alternative names: None
Other associated named signs: Cobweb sign, beak sign, and the intimointimal intussusception sign
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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