Unusual hemodynamics and pseudolesions of the noncirrhotic liver at CT

Recognition of pseudolesions of the liver at computed tomography (CT) is im portant because of their close resemblance to primary liver cancers or meta stases. Two types of pseudolesion in the noncirrhotic liver include that du e to transient extrinsic compression, typically caused by ribs or the diaph ragm, and that due to a "third inflow" of blood from other than the usual h epatic arterial and portal venous sources: the cholecystic, parabiliary, or epigastric-paraumbilical venous system. Although the location of both type s of pseudolesion are characteristic, their appearances at CT during arteri al portography and CT during selective angiography vary from nonenhanced lo w-attenuation areas to well-enhanced high-attenuation areas, depending on t he amount and timing of the inflow and presence or absence of focal metabol ic alteration of the hepatocytes. Radiologists need to understand the under lying mechanism of these pseudolesions to better recognize the wide range o f their appearances at CT.