Corpus: Common bile duct

The ductus choledochus is a part of the extrahepatic bile ducts. It is the continuation of the common hepatic duct after the exit of the cystic duct and channels bile from the liver or gallbladder into the duodenum.

The choledochal duct runs in the hepatoduodenal ligament above the duodenum and crosses under it in its upper part to pass behind the pancreatic head. Intertwined with the pancreatic tissue, the ductus choledochus runs to the dorsal side of the lower duodenum and enters its wall.

Due to its course in the duodenal wall, the ductus choledochus raises a longitudinal fold of mucous membrane (plica longitudinalis duodeni). At the end of this mucosal fold, the choledochal duct opens into the lumen of the duodenum in the papilla duodeni major.

The choledochal duct often joins the pancreatic duct before entering the greater duodenal papilla and forms a bulge, the hepatopancreatic ampulla. In such cases, the pancreatic duct and large bile duct flow together into the duodenum.

The two-layered wall of the choledochal duct consists of a tunica mucosa with prismatic epithelium and a lamina propria of connective tissue with collagenous and elastic fibres. Mucous glands are embedded in the tunica mucosa, which improve the gliding ability of the bile.

The end section of the choledochal duct contains ring-shaped fibres of smooth muscle that form spiral coils. The unit of these muscle fibres is called the sphincter oddi and causes the duodenum to close off from the choledochal duct during the resting phases of digestion.

Obstruction of the choledochal duct by a tumour or a gallstone leads to an obstructive jaundice. Diagnostically, the choledochal duct can be visualised using various imaging techniques, including:

• Sonography or endosonography
• Computed tomography (CT)
• Endoscopic retrograde cholangiopancreatography (ERCP)
• Percutaneous transhepatic cholangiography (PTC)
• Magnetic resonance cholangiopancreatography (MRCP)

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