Pseudothrombosis of the portal vein

Imaging description On early post-contrast CT studies of the abdomen, the portal vein sometimes appears to contain a central ill-defined filling defect that disappears on more superior images. This “pseudothrombosis” is due to the laminar mixing of enhanced blood from the splenic vein with less enhanced blood from the superior mesenteric vein (Figure 16.1) [1]. This pseudolesion resolves on later phases of enhancement. Importance This may be mistaken for a true tumor or bland thrombus of the portal vein, resulting in unnecessary follow-up investigations and patient anxiety. Typical clinical scenario Pseudothrombosis of the portal vein is generally only seen on early post-contrast CT images, such as CT arteriography. Differential diagnosis Occasionally arterioportal shunting in the liver can cause premature opacification of a portal vein branch, and the resulting mixing of opacified and unopacified portal venous blood can result in a “pseudothrombus” (Figure 16.2). Other than these considerations, cross-sectional imaging has high accuracy in the identification of portal vein thrombus, and the only main limitation is that a diminutive portal vein can sometimes be mistaken for chronic thrombosis [1]. Teaching point The appearance of an apparent filling defect in the portal vein on early post-contrast CT images should be correlated with later phase images, because occasionally mixing artifacts may result in pseudothrombosis in the arterial phase.