Liver and Biliary Tree
The common hepatic duct (CHD) is joined on the right side by the cystic duct (from the gallbladder) to form the common bile duct (CBD) in the free edge of the lesser omentum.
The CBD descends posterior to the first part of the duodenum and lies in a groove on the posterior surface of the head of the pancreas.
As a rule, the CBD joins the main pancreatic duct (of Wirsung) to form a dilated common vestibule – the ampulla of Vater. The opening and closing of the ampulla in the duodenum is guarded by the sphincter of Oddi. Occassionally, the bile and pancreatic ducts open separately into the duodenum.
The bile ducts arise as biliary capillaries between hepatocytes. The bile capillaries merge to form intrahepatic bile ducts.
Intrahepatic Bile Duct
The intrahepatic bile ducts are branched into eight segments, which correspond with the eight segments of the liver as defined by Couinaud. These segments are fairly constant but there is considerable variation in the arrangements of their junction or confluence.
The intrahepatic ducts can be normally visualised in up to 40% of normal people on contrast enhanced CT or ultrasound.
The intralobular ducts which are the ducts formed from each segment, merge to form two main intrahepatic trunks from the right and left lobes of the liver.
The right and left hepatic ducts are up to 3 mm in diameter. The segmental ducts are smaller and taper to the periphery.
The right and left hepatic ducts merge outside the liver at the porta hepatis to form the common hepatic duct. The common hepatic duct is 3-4 cm in length, and up to 6 mm in diameter. The common hepatic duct descends along the free edge of the lesser omentum, and is joined on the right side by the cystic duct.
The cystic duct runs posteriorly and inferiorly from the neck of the gallbladder for 3-4 cm within the right free edge of the lesser omentum, at which point it merges with the common hepatic duct (CHD) to form the common bile duct (CBD).