The “Parallel Channel” Sign of Biliary Tree Enlargement in Mild to Moderate Degrees of Obstructive Jaundice
Ultrasound has been shown to be of value in the diagnosis of obstructive jaundice. The previously reported criteria using ultrasound for diagnosing obstructive jaundice have consisted of: (a) the demonstration of an enlarged common bile duct or (b) a characteristic pattern of radiating, sonolucent, tubular channels from the portal hepatis representing enlarged bile ducts. An enlarged common bile duct may be differentiated from the portal vein in that the latter has a characteristic “comma” shape on longitudinal sections. However, these findings are seen only in advanced stages of obstructive jaundice, and are usually associated with a bilirubin greater than 10 mg.%. Previous investigators have stressed the importance of not confusing branches of the portal venous system with enlargement of the biliary tree. Demonstration of the confluence between suspected enlarged bile ducts and the common bile duct by serial sections has been advised before diagnosing enlarged bile ducts. However, this may be technically difficult to demonstrate. To date, a reliable means using ultrasound in distinguishing a minimally enlarged biliary tree due to obstructive jaundice from the portal venous system within the liver has not been established.