Ultrasonographic identification of dilated intrahepatic bile ducts and their differentiation from portal venous structures.

The appearance of dilated intrahepatic bile ducts was evaluated on ultrasonograms of 50 patients with proven extrahepatic biliary obstruction. Five characteristic changes allowed differentiation between biliary and portal venous systems. These changes included: 1) alteration in the anatomic pattern adjacent to the main right portal venous segment and the main portal vein bifurcation. 2) Irregular walls of dilated bile ducts. 3) Stellate confluence of dilated bile ducts. 4) Acoustic enhancement by dilated bile ducts. 5) Peripheral location of dilated bile ducts. Many patients exhibited more than one of these findings. Parasagittal scans of the main right portal vein were the most sensitive for detection of intrahepatic ductal dilatation. Recognition of the characteristic changes and knowledge of the portal venous anatomy makes it possible to diagnose extrahepatic biliary obstruction with a high degree of confidence.