CT of portal venous occlusion.

Thrombosis of a portion of the portal venous system can be directly imaged by contrast-enhanced CT as a low-attenuation lesion within the involved portal venous segment with or without expansion of the vessel or enhancement at the margin of the thrombus. Collateral venous pathways are often evident, which provide supporting evidence of the occlusion. Alterations in portal venous blood flow lead to metabolic disturbances in the liver and to abnormalities in parenchymal enhancement during dynamic CT scanning, and these changes are manifested as abnormalities in hepatic parenchymal density. The detection of portal venous thrombosis or occlusion, collateral veins, or abnormal liver enhancement should initiate a search for the diseases that cause these abnormalities.