Associate Professor of Radiology University of Palermo School of Medicine, Italy
The liver has three vascular systems: the portal vein, the hepatic vein, and the hepatic artery. The vascular disorders that will be presented in this talk can be divided into disorders of the inflow and disorders of the outflow. Disorders of the inflow are hepatic artery thrombosis and portal vein trhombosis, that can be divided into acute, subacute and chronic.
Arteriovenous shunts are among the causes of transient hepatic perfusion disorders and may simulate a hypervascular hepatic lesion on arterial-phase imaging. A more common cause of hepatic perfusion disorders is occlusion of a portal venous branch with compensatory increased arterial flow, causing arterial phase hyperenhancement. These perfusion pseudolesions can usually be distinguished from tumor by their peripheral location, wedge shape, lack of mass effect, and isoattenuation with liver on all other phases. Cavernous transformation of the portal vein occurs with long-standing portal vein thrombosis due to the development of periportal, serpiginous collaterals around the occluded main portal vein (Fig. 3). The atropy hyhypertrophy complex (hypertrophy of the caudate lobe, left lateral segment atrophy and a normal or enlarged segment IV segment) is frequently observed in patients with cavernous transformation of the portal vein. Disorders of the outflow are typically associated with the occurrence of dilatation of the hepatic capillaries, known as sinusoids.. Most of the time this condition is caused by hepatic venous outflow obstruction, which results in vascular stasis and congestion of hepatic parenchyma. In this setting, hepatic sinusoidal dilatation can be related to pericardial disease, heart failure, compression or thrombosis of the hepatic veins or inferior vena cava (i.e. Budd Chiari syndrome) or central veins/sinusoids involvement (i.e. sinusoidal obstruction syndrome). Nevertheless, some extra hepatic inflammatory conditions (such as pyelonephritis, cholecystitis, pneumonia, pancreatitis, intestinal bowel disease and others) may be associated with hepatic sinusoidal dilatation without concurrent venous outflow obstruction. On contrast-enhanced cross-sectional imaging, hepatic sinusoidal dilatation is typically characterized by a mottled, reticular enhancement of the liver, usually referred to as “mosaic” pattern. Other hepatic and extra-hepatic imaging features, such us the dilatation of the hepatic veins or the presence of ascites, can help in identifying the cause of sinusoidal dilatation.