Understanding transient hepatic attenuation differences.

Transient hepatic attenuation differences (THADs) are the imaging manifestation of regional variations in the balance between hepatic arterial, portal venous, and third inflow sources of hepatic blood flow. THADs are typically wedge-shaped hypervascular regions visible on the hepatic arterial phase, and fade to isodense on venous and delayed phases. They are commonly seen in the setting of locally diminished portal venous inflow. Familiarity with the characteristic appearance and the physiology of THADs should permit discrimination of these fascinating pseudolesions from true space occupying masses.