Summary
The bile duct (formerly known as the common bile duct) is a part of the biliary tract. It is formed by the union of the common hepatic duct and cystic duct. It ends by uniting with the pancreatic duct to form the hepatopancreatic ampulla. It possesses its own sphincter to enable regulation of bile flow. The bile duct is some 6–8 cm long, and normally up to 8 mm in diameter. Its proximal supraduodenal part is situated within the free edge of the lesser omentum. Its middle retroduodenal part is oriented inferiorly and right-ward, and is situated posterior to the first part of the duodenum, and anterior to the inferior vena cava. Its distal paraduodenal part is oriented still more right-ward, is accommodated by a groove upon (sometimes a channel within) the posterior aspect of the head of the pancreas, and is situated anterior to the right renal vein. The bile duct terminates by uniting with the pancreatic duct (at an angle of about 60°) to form the hepatopancreatic ampulla. The distal extremity of the bile duct invariably features its own sphincteric muscle (the pancreatic duct and the hepatopancreatic ampulla usually possess sphincters to allow the flow of pancreatic juice to be regulated independently, however, these two can be absent). Several problems can arise within the common bile duct, usually related to its obstruction. Opinions vary slightly on the maximum calibre of a normal CBD, but 6mm is one accepted upper limit of normal with a further 1mm diameter allowed for each decade over 60 years. It normally gets slightly dilated after cholecystectomy, with upper limit (95% prediction interval) being about 10 mm after a few months. On abdominal ultrasonography, the common bile duct is most readily seen in the porta hepatis (where the CBD lies anterior to the portal vein and hepatic artery). The absence of Doppler signal distinguishes it from the portal vein and hepatic artery. File:Ultrasonography of common hepatic duct, labeled.jpg|Borderline of a dilated perihilar bile duct, measuring 8 mm.
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