ULTRASOUND OF THE BILIARY TREE - Normal
The biliary tree descends from the canaliculi at the hepatocytes, gradually enlarging and merging to the right and left hepatic ducts.
These 2 merge at porta hepatis to form the Common Hepatic Duct(CHD).
The Common Bile Duct (CBD) is formed by the junction of the cystic duct with the CHD.
The CBD traverses through the head of the pancreas entering the duodenum at the Ampulla of Vater through the Sphyncter of Oddi.
Prior to draining into the duodenum the CBD is joined by the pancreatic duct.
A smaller accessory pancreatic duct and sphincter is usually present (but rarely visible) from the dorsal pancreatic embyologic rotation.
|Anatomy of the Biliary System
A common anatomic variation is to have an extrahepatic junction of the right/left hepatic ducts.(20% of people)
It is useful to make note of this in the report, particularly if it is a very distal junction. During cholecystectomy surgery, the common duct is cannulated to image for duct calculi which may be missed. Also to avoid mistaking the RHD for the cystic duct.
||A common variant is the common bile duct coursing below the hepatic artery. In colour (mouse over) it proves the hepatic artery (in blue) is anterior.
Ultrasound of the Biliary Tree - Protocol
Ultrasound is the primary tool for assessment of the structure of the biliary tree.
Whilst studies on have been performed on functional assessment of CBD diameter (pre/post fatty meal), they are not easily or objectively reproducable.
Physiological assessment of gallbladder function is best performed with Nuclear medicine or CT cholangiography.
The source of obstruction may be:
Image the CBD from the liver to the ampulla. Measure it in the widest and follow it to the thinnest portion extrahepatically.