Biliary Tract Imaging

Biliary Anatomy & Imaging Modalities - Map & Toolkit

• Anatomy Overview:

  • R/L Hepatic Ducts → Common Hepatic Duct (CHD; ≤6mm)
  • CHD + Cystic Duct → Common Bile Duct (CBD; ≤7mm; ↑1mm/decade >60y; post-cholecystectomy up to 10-12mm)
  • Gallbladder: Fundus, Body, Neck, Hartmann's Pouch
  • CBD segments: Supraduodenal, Retroduodenal, Pancreatic, Intramural
  • Ampulla of Vater, Sphincter of Oddi

• Imaging Toolkit:

  • USG: 1st line; stones (shadow), dilatation.
  • CT: Complications, Ca++ stones, staging.
  • MRCP: Best non-invasive ductal view; T2W.

    ⭐ MRCP is highly sensitive for choledocholithiasis, often obviating diagnostic ERCP.

  • ERCP: Dx & Rx; invasive.
  • HIDA: Functional (GB EF), acute cholecystitis, leaks.
  • PTC: Invasive drainage if ERCP fails_.

Gallstone Disease & Complications - Pebble Problems & Pain

• Cholelithiasis (Gallstones):

  • Types: Cholesterol (most common, radiolucent), Pigment (black/brown, radiopaque).
  • Risk factors (📌 4 F's): Female, Forty, Fertile, Fat.
  • USG: Hyperechoic, posterior acoustic shadowing, mobile.

• Complications & Key Imaging Signs:

  • Acute Cholecystitis:
    • USG: GB wall thickening >3-4 mm, pericholecystic fluid, sonographic Murphy's sign.
    • HIDA: Non-visualization of GB (confirmatory).
  • Choledocholithiasis (CBD stones):
    • USG: CBD dilation >6-7 mm; stone may be seen.
    • MRCP: Diagnostic TOC. ERCP: Therapeutic.

    ⭐ MRCP is the non-invasive gold standard for diagnosing choledocholithiasis, especially when USG is inconclusive.

  • Acute Cholangitis: (Infection + Obstruction)
    • 📌 Charcot's Triad: Jaundice, Fever, RUQ Pain.
    • Imaging: CBD dilation, stones, +/- biliary gas.
  • Gallstone Ileus: (Fistula → SBO)
    • 📌 Rigler's Triad: Pneumobilia, SBO, ectopic gallstone.
  • Mirizzi Syndrome: Extrinsic CBD compression by cystic duct stone.
  • Porcelain Gallbladder: Wall calcification (↑ cancer risk).

Biliary Strictures & Tumors - Tight Squeezes & Bad News

• Biliary Strictures:
  • Causes: Benign (post-op [MC], PSC, IgG4, pancreatitis, stones) vs. Malignant (CCA, pancreatic/GB ca, mets).
  • MRCP: Best non-invasive; shows site, length, dilatation.
  • ERCP: Dx & Rx (biopsy, stenting).
  • Features: Benign (smooth, concentric, tapering) vs. Malignant (irregular, eccentric, abrupt, mass, shouldering).
• Cholangiocarcinoma (CCA):
  • Types & Key Features:
    • Intrahepatic: Mass-forming (MC), periductal-infiltrating; delayed enhancement, capsular retraction.
    • Perihilar (Klatskin): MC type; stricture at confluence, upstream dilatation. Bismuth-Corlette classification.
    • Distal: Stricture in distal CBD; "double duct" sign.
  • Risk Factors: PSC, choledochal cysts, liver flukes (Opisthorchis).
  • Staging: CT/MRI for mass, vascular invasion, mets.

  ⭐ Klatskin tumor (perihilar CCA) is most common. Bismuth-Corlette classification guides resectability.

Congenital Biliary Anomalies - Twisted Tubes from Tots

• Biliary Atresia:
  • Obliteration of extrahepatic ducts; presents with neonatal jaundice.
  • USG: Triangular cord (TC) sign (fibrous tissue anterior to portal vein, >4mm thick), absent/small gallbladder (GB).
  • HIDA scan: Failure of tracer excretion into bowel. MRCP confirms diagnosis.
• Choledochal Cysts:
  • Congenital cystic dilatations of the biliary tree. Todani classification (Types I-V).
  • USG is initial imaging; MRCP is definitive for classification & surgical planning.
  • ↑ Risk of cholangiocarcinoma.

  ⭐ Todani Type I (fusiform or cystic dilatation of the common bile duct) is the most common type, accounting for 80-90% of cases.

• Caroli's Disease (Todani Type V):
  • Non-obstructive, saccular or fusiform dilatation of intrahepatic bile ducts.
  • Imaging: "Central dot sign" on CT/MRI (portal vein radicle surrounded by dilated bile duct).
  • Associated with autosomal recessive polycystic kidney disease (ARPKD) and hepatic fibrosis.
• Biliary Hypoplasia:
  • Paucity of intrahepatic bile ducts; may be syndromic (e.g., Alagille syndrome) or non-syndromic.
• Aberrant Bile Ducts (e.g., Ducts of Luschka):
  • Anatomic variants; usually asymptomatic. Can be injured during cholecystectomy, leading to bile leaks.

High‑Yield Points - ⚡ Biggest Takeaways

• USG: Initial choice for gallstones & cholecystitis.
• MRCP: Gold standard for non-invasive biliary tree evaluation (e.g., choledocholithiasis, strictures).
• HIDA scan: Best for acute cholecystitis (non-visualization of GB) & biliary atresia (no bowel excretion).
• ERCP: Diagnostic & therapeutic for biliary obstruction (stone removal, stenting).
• Courvoisier's law: Palpable, non-tender gallbladder + jaundice = likely malignant obstruction.
• Porcelain gallbladder: ↑ risk of gallbladder carcinoma.
• Klatskin tumor: Cholangiocarcinoma at hepatic duct bifurcation.