Introduction
This topic covers the imaging of the biliary system (gallbladder, cystic duct, common bile duct and intrahepatic ducts) and the main gallbladder diseases: gallstone disease, acute and chronic cholecystitis, gallbladder polyps, adenomyomatosis, porcelain gallbladder and gallbladder carcinoma. The exam answer should name the best first-line modality, explain how the others complement it, and describe the typical findings and complications of each disease.
Imaging modalities of the biliary system
Ultrasound is the first-line examination for suspected biliary disease. Other modalities are chosen to answer a specific question, such as whether the common bile duct is obstructed or whether there is a complication.
Ultrasound findings in gallstone disease
- Gallstones: hyperechoic foci with posterior acoustic shadowing; they move with change of patient position (mobile stones).
- Sludge: low-level echoes layering dependently without shadowing, often in immobile gallbladders.
- Normal gallbladder: wall thinner than about 3 mm, no distension, and a common bile duct of about 6 mm (up to about 7 mm in older patients).
- Biliary colic is caused by transient obstruction of the cystic duct by a stone; there is pain without inflammation, and the gallbladder is usually normal in wall and size between attacks.