cystic duct

The cystic duct is a 3-4 cm tubular structure that joins the neck of the gallbladder to the common hepatic duct, forming the common bile duct (CBD). Internally, it contains mucosal folds called the spiral valves of Heister, which help regulate bile flow but do not fully prevent reflux or filling. Bile secreted by hepatocytes flows through the common hepatic duct and, between meals, is diverted through the cystic duct into the gallbladder for concentration and storage (via active Na+ absorption). After a fatty meal, CCK release causes gallbladder contraction and relaxation of the sphincter of Oddi, propelling bile back through the cystic duct into the CBD and into the duodenum.

Clinical significance: Obstruction of the cystic duct, most commonly by a gallstone (calculous cholecystitis) or occasionally by biliary sludge, edema, or functional dyskinesia (acalculous cholecystitis in critically ill patients), leads to gallbladder distension, bile stasis, and secondary bacterial infection (E. coli, Klebsiella, Enterococcus), resulting in acute cholecystitis. Presents with RUQ pain (often radiating to the right scapula), fever, and a positive Murphy's sign. Diagnosis is via ultrasound (gallbladder wall thickening, pericholecystic fluid, sonographic Murphy's sign) or HIDA scan (nonfilling of the gallbladder indicates cystic duct obstruction). Treatment is cholecystectomy, ideally within 72 hours of symptom onset.

Mirizzi syndrome is a complication where a gallstone impacted in the cystic duct or gallbladder neck compresses the adjacent common hepatic duct, causing obstructive jaundice.

Surgical anatomy: During laparoscopic cholecystectomy, the cystic duct and cystic artery are identified and ligated within the Triangle of Calot (bounded by the cystic duct, common hepatic duct, and inferior border of the liver) to avoid injury to the common bile duct or right hepatic artery ('critical view of safety').