Common bile duct
The common bile duct, sometimes abbreviated CBD, is a duct in the gastrointestinal tract of organisms that have a gallbladder. It is formed by the union of the common hepatic duct and the cystic duct. It is later joined by the pancreatic duct to form the ampulla of Vater. There, the two ducts are surrounded by the muscular sphincter of Oddi.
When the sphincter of Oddi is closed, newly synthesized bile from the liver is forced into storage in the gallbladder. When open, the stored and concentrated bile exits into the duodenum. This conduction of bile is the main function of the common bile duct. The hormone cholecystokinin, when stimulated by a fatty meal, promotes bile secretion by increased production of hepatic bile, contraction of the gallbladder, and relaxation of the sphincter of Oddi.
Clinical significance
Several problems can arise within the common bile duct. A diameter of more than 8 mm is regarded as abnormal dilatation and is a sign of cholestasis.| Normal | ≤ 8 mm |
| Mild dilatation | 8 – 12 mm |
| Moderate dilatation | 12 – 16 mm |
| Severe dilatation | 16 – 20 mm |
| Extremely severe dilatation | >20 mm |
It normally gets slightly dilated after cholecystectomy, with upper limit being about 10 mm after a few months.
On abdominal ultrasonography, the common bile duct is generally seen most readily in the perihilar area. The absence of Doppler signal distinguishes it from the portal vein and hepatic artery.
If clogged by a gallstone, a condition called choledocholithiasis can result. In this clogged state, the duct is especially vulnerable to an infection called ascending cholangitis. Very rare deformities of the common bile duct are cystic dilations, choledochoceles, and biliary atresia.