Evaluation of the portal venous system: complementary roles of invasive and noninvasive imaging strategies.

Evaluation of the portal venous system is required in several clinical circumstances, including before and after liver transplantation, before creation of a transjugular intrahepatic portosystemic shunt, in the clinical setting of bowel ischemia, or to evaluate varices. Several noninvasive modalities (magnetic resonance [MR] imaging and MR angiography, computed tomography [CT], and ultrasound [US]) are available for evaluation of the portal venous system in addition to the invasive angiographic methods. In most clinical circumstances, either CT or MR imaging and MR angiography in combination with US of the liver vasculature will allow complete evaluation of the portal venous system. Invasive evaluation of the portal venous system is necessary when results of the noninvasive tests disagree or are inconclusive. Angiography may also be indicated whenever noninvasive tests indicate occlusion of the portal venous system, as this is often a crucial clinical question and false-positive results can occur with the noninvasive tests.