common bile duct

Embryologically and anatomically, the common bile duct is formed by the confluence of the cystic duct (from the gallbladder) and the common hepatic duct (formed by the right and left hepatic ducts draining the liver). The CBD travels within the hepatoduodenal ligament (part of the lesser omentum), running along the free edge anterior to the portal vein and to the right of the hepatic artery proper (mnemonic: CBD-Portal vein-Hepatic artery = 'CBD is most lateral, artery most medial, duct most anterior'). It descends posterior to the superior (first) part of the duodenum, then passes through or behind the head of the pancreas, where it joins the main pancreatic duct (duct of Wirsung) to form the hepatopancreatic ampulla (ampulla of Vater), which empties into the second part of the duodenum at the major duodenal papilla. The sphincter of Oddi controls flow of bile and pancreatic secretions into the duodenum and is regulated by CCK (relaxes sphincter, contracts gallbladder) in response to fatty meals.

Clinical significance: Obstruction of the CBD leads to conjugated hyperbilirubinemia, dark urine, pale/clay-colored stools, pruritus, and elevated alkaline phosphatase and GGT (cholestatic pattern). Common causes include choledocholithiasis (gallstones), pancreatic head carcinoma (painless jaundice), cholangiocarcinoma, and strictures (e.g., from primary sclerosing cholangitis). Courvoisier sign refers to a palpable, non-tender gallbladder with jaundice, classically associated with pancreatic head cancer rather than gallstones (since gallstone-related chronic inflammation typically causes a fibrotic, non-distensible gallbladder). Ascending cholangitis, a life-threatening infection of the biliary tree, presents with Charcot triad (fever, jaundice, RUQ pain) or Reynolds pentad (add hypotension and altered mental status) and is often due to CBD obstruction with secondary bacterial infection, commonly treated with antibiotics and biliary decompression (ERCP).

Surgical relevance: The CBD is at risk of injury during cholecystectomy, particularly if the cystic duct is mistaken for the CBD (critical view of safety is used to prevent this). ERCP is both diagnostic and therapeutic for CBD stones, strictures, and tumors.