High-resolution real-time ultrasound in the evaluation of the normal and obstructed biliary tract.

Ultrasound was found to be useful in the evaluation of jaundice. Extrahepatic obstruction can be diagnosed by the presence of dilated intra- or extrahepatic bile ducts. Using a high-resolution real-time mechanical sector scanner, it was possible to show the common hepatic duct as it passes anterior to the right portal vein in 98 out of 100 consecutive adults without biliary tract disease. At this level, the normal duct measures 4 mm or less in internal diameter. All patients with a duct larger than 5 mm thus far have had either biliary tract obstruction or previous cholecystectomy.