hepatic duct

ANATOMY - Intrahepatic bile canaliculi drain into bile ductules (canals of Hering), then into interlobular ducts, and then into segmental ducts. These form the right and left hepatic ducts. - Right hepatic duct: drains the right lobe (segments V-VIII). Left hepatic duct: drains the left lobe (segments II-IV) and usually the caudate lobe. - The right and left hepatic ducts exit the liver at the porta hepatis and fuse to form the common hepatic duct (CHD). The fusion is the hepatic duct confluence. - The CHD runs in the hepatoduodenal ligament (free edge of the lesser omentum) and is joined by the cystic duct from the gallbladder. Together they form the common bile duct (CBD). - The CBD joins the main pancreatic duct at the hepatopancreatic ampulla (of Vater) and empties into the 2nd part of the duodenum at the major duodenal papilla. The sphincter of Oddi controls this opening. - Portal triad: the bile duct lies anterolateral (right), the hepatic artery proper lies anteromedial (left), and the portal vein lies posterior. - Calot's triangle (cystohepatic triangle): borders are the cystic duct, the common hepatic duct, and the inferior edge of the liver (the older definition uses the cystic artery in place of the liver edge). The cystic artery, usually from the right hepatic artery, runs through it. It is the key landmark in cholecystectomy.

HISTOLOGY AND PHYSIOLOGY - Ducts are lined by simple cuboidal to columnar epithelium (cholangiocytes). Cholangiocytes modify bile by secreting bicarbonate and water. This secretion is stimulated by secretin. - Bile is made by hepatocytes. It contains bile salts, phospholipids (lecithin), cholesterol, bilirubin, and electrolytes. Bile salts are the major driver of bile flow. - Bile is stored and concentrated in the gallbladder. CCK, released by I cells in response to fatty acids and amino acids, causes gallbladder contraction and sphincter of Oddi relaxation.

CLINICAL CORRELATES - Obstruction (cholestasis) causes conjugated (direct) hyperbilirubinemia, elevated ALP and GGT, pruritus, jaundice, dark urine, and pale (acholic) stools. Causes include choledocholithiasis, strictures, tumors, and primary sclerosing cholangitis. - Mirizzi syndrome: a gallstone impacted in the cystic duct or gallbladder neck compresses the common hepatic duct. This causes obstructive jaundice. - Iatrogenic bile duct injury: the most feared complication of laparoscopic cholecystectomy. It happens when the CHD or CBD is mistaken for the cystic duct. It is avoided by obtaining the "critical view of safety." - Cholangitis: infection of obstructed bile ducts (usually E. coli, Klebsiella, Enterococcus). Charcot triad is fever, jaundice, and RUQ pain. Reynolds pentad adds hypotension and altered mental status. Treatment is antibiotics and biliary decompression (ERCP). - Primary sclerosing cholangitis (PSC): associated with ulcerative colitis and p-ANCA. Imaging shows a "beaded" appearance of intra- and extrahepatic ducts. Risk of cholangiocarcinoma. - Primary biliary cholangitis (PBC): autoimmune destruction of small intrahepatic ducts. It occurs in middle-aged women, with anti-mitochondrial antibodies (AMA) and elevated IgM. - Cholangiocarcinoma: a malignancy of the bile duct epithelium. A Klatskin tumor arises at the confluence of the right and left hepatic ducts (perihilar), is the most common location, and presents with painless jaundice. Risk factors include PSC, Clonorchis sinensis (liver fluke), choledochal cysts, and Caroli disease. - Biliary atresia: fibro-obliteration of extrahepatic bile ducts in neonates. It presents with persistent conjugated hyperbilirubinemia, acholic stools, and jaundice after 2 weeks of life. Treatment is the Kasai procedure (hepatoportoenterostomy), and liver transplant is often needed eventually. - Choledochal cysts: congenital cystic dilations of the bile ducts. They are associated with cholangiocarcinoma risk. - Courvoisier sign: a palpable, nontender gallbladder with jaundice, suggesting malignant distal biliary obstruction (e.g., pancreatic head cancer), not stones.

HIGH-YIELD PEARL Hepatic ducts are proximal to the cystic duct junction, so obstruction there causes jaundice without gallbladder distension. Obstruction of the CBD distal to the cystic duct junction can cause gallbladder distension.