What imaging feature is most characteristic of hepatocellular carcinoma on multiphasic CT or MRI?

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Hepatocellular carcinoma is best recognized on multiphasic CT or MRI by its arterial phase hyperenhancement with venous or delayed washout. This pattern reflects the tumor’s reliance on arterial blood supply: during the arterial phase, the lesion shows rapid contrast uptake and becomes brighter than the surrounding liver. In the portal venous and delayed phases, the liver parenchyma enhances via the portal system while the tumor, which lacks sustained portal supply, loses the contrast and appears relatively hypoenhanced, producing washout. This combination—bright in the arterial phase followed by washout in later phases—is highly characteristic of HCC in at-risk patients. Additional features such as a capsule or pseudocapsule can accentuate the appearance on delayed images. The other options don’t match this characteristic evolution: portal venous wash-in is not typical for HCC, diffuse hypointensity is not the classic focal vascular pattern, and no enhancement would not reflect the tumor’s arterial vascularity.