The cystic duct: normal anatomy and disease processes.

The cystic duct can be depicted with a variety of imaging modalities but is optimally visualized with direct cholangiography or magnetic resonance cholangiopancreatography. Nevertheless, unrecognized anatomic variants of the cystic duct may cause confusion on imaging studies and complicate subsequent surgical, endoscopic, and percutaneous procedures. Primary entities involving the cystic duct include calculous disease, Mirizzi syndrome, cystic duct-duodenal fistula, biliary obstruction, neoplasia, and primary sclerosing cholangitis. The cystic duct may also be secondarily involved by adjacent malignant or inflammatory processes. Postoperative alterations are seen after liver transplantation or cholecystectomy when a portion of the cystic duct is left behind as a remnant. Recognized postoperative complications include retained cystic duct stones, cystic duct leakage, and malposition of T tubes in the remnant. Pitfalls encountered in cystic duct imaging include pseudocalculous defects from overlap of the cystic duct and common bile duct, underfilling of the cystic duct during direct cholangiography, and admixture defects at the cystic duct orifice. Pseudomass or pseudotumor defects may result from an impacted cystic duct stone or from a tortuous, redundant cystic duct. Familiarity with the imaging appearance of the normal cystic duct, its anatomic variants, and related disease processes facilitates accurate diagnosis and helps avoid misinterpretation.