Which imaging feature best differentiates portal cavernoma from Budd-Chiari syndrome?

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The main point is where the obstruction lies in liver venous drainage. Portal cavernoma results from portal vein thrombosis, so imaging shows cavernous transformation around the porta hepatis—many tiny collateral vessels replacing the blocked portal vein. Budd-Chiari syndrome, on the other hand, is hepatic venous outflow obstruction, so imaging features emphasize hepatic vein or IVC thrombosis with congestive liver changes, often with caudate lobe hypertrophy.

Beading of the bile ducts is not a feature of Budd-Chiari; that pattern is classic for primary sclerosing cholangitis, which makes that choice a poor differentiator here. Liver size alone isn’t diagnostic, and saying imaging can’t differentiate misses the clear distinction between portal venous obstruction versus hepatic venous outflow obstruction.

So the best differentiator is the presence of cavernous transformation of the portal vein indicating portal vein thrombosis, as opposed to hepatic vein thrombosis and related outflow obstruction seen in Budd-Chiari.