The extrahepatic biliary system is composed of the bile ducts and the gallbladder (Figure 44-1). In 70% of patients, the common bile duct and pancreatic duct join at the ampulla of Vater and have a common duodenal opening. In the other 30%, the pancreatic and bile ducts open separately. The common bile duct has a luminal diameter of 0.5–0.7 cm in the adult.
Anatomy of the biliary system.
Histologically, the entire biliary tract is lined by mucus-secreting columnar epithelium. In the gallbladder, the epithelium is thrown up into delicate folds, and mucous glands are buried deeply in the smooth muscle wall (Aschoff-Rokitansky sinuses).
The biliary system stores and delivers the bile secreted by the liver into the duodenum, with the gallbladder acting as a reservoir in which the bile is stored and concentrated (from about 1000 mL/d down to 50 mL/d). The gallbladder is not required for adequate functioning of the system. Bile is an alkaline fluid that contains the excretory bilirubin pigments, bile acids and bile salts, cholesterol, inorganic ions, and mucus. Cholesterol, which is insoluble in water, is maintained in solution by the formation of complexes with the hydrophilic bile salts and lecithin.
Several types of pain occur in diseases of the extrahepatic biliary system. Biliary colic is severe intermittent pain in the right upper abdomen that radiates to the back and right shoulder. It is caused by increased muscular contraction of the bile duct and occurs when there is bile duct obstruction. Vague epigastric pain (dyspepsia), which may be aggravated by ingestion of fatty foods, is common in patients with gallstones and chronic cholecystitis. The mechanism of this pain is unknown. Constant right upper abdominal pain, often severe, occurs in acute cholecystitis when extension of inflammation involves the pain-sensitive parietal peritoneum.
Courvoisier's law. A: When obstructive jaundice is caused by a calculus in the common bile duct, there is no enlargement of the gallbladder. B: When obstructive jaundice is caused by anything other than gallstones, the gallbladder is enlarged. Note that many exceptions exist to this rule.
Obstruction of the common bile duct results in obstructive jaundice. The biliary system undergoes dilation proximal to the obstruction, and bile backs up in the liver (cholestasis). The gallbladder undergoes enlargement when it is normal; in patients who have gallstones and fibrotic thickening of the gallbladder wall, gallbladder enlargement does not occur (Courvoisier's law).
Cholecystography & Cholangiography
The biliary tract may be outlined by a radiopaque dye, permitting evaluation of its anatomy. The dye may be given orally or intravenously to be excreted in ...