Biliary System

Pathology of the Biliary Tree

• Overview of Biliary Tree

  • Originates in the liver; the proximal section is where bile is produced.

  • Distal section is the common bile duct closest to the pancreatic head.

  • Divisions:

    • Extrahepatic: Common bile duct, cystic duct, and part of common hepatic duct.

    • Intrahepatic: All other portions of the biliary tree.

Dilated Intrahepatic Ducts

• Differentiation Criteria:

  • Parallel Channel/Shotgun Sign: Dilated ducts’ size parallels the adjacent portal vein, increasing towards porta hepatis.

  • Irregularity: Biliary ducts are more tortuous than accompanying portal veins.

  • Stellate Confluence: Star-shaped branching of bile ducts.

  • Acoustic Enhancement: Bile ducts have less attenuation than blood, leading to posterior acoustic enhancement.

  • Color Doppler: Differentiates portal vein (fills with color) from bile ducts (do not fill with color).

Biliary Obstruction

• Common Level: Usually occurs at the distal common bile duct.

• Consequence of Obstruction:

  • Extrahepatic ducts typically dilate first.

• Causes of Obstruction:

  • Most Common: Choledocholithiasis (bile duct stones).

  • Other causes include chronic and acute pancreatitis, pancreatic carcinoma.

• Clinical Significance: Biliary obstruction is a common cause of jaundice.

Cholangitis

• Definition: Inflammation of biliary ducts.

  • Wall thickness > 5 mm.

• Symptoms: Right upper quadrant (RUQ) pain, Fever, Jaundice.

• Sonographic Findings:

  • Varying biliary dilatation, biliary sludge, thickened bile duct walls.

Pneumobilia

• Definition: Presence of air within biliary tree.

• Association: Recent biliary or gastric surgery, emphysematous cholecystitis.

• Sonographic Appearances:

  • Echogenic linear foci with posterior ring down artifact.

Choledocholithiasis

• Definition: Presence of stones in the ductal system.

  • Most stones derive from gallbladder.

• Clinical Relevance: Common duct stones are a sequela of calculous cholecystitis.

  • Stones may affect Vater’s ampulla and protrude into the duodenum.

Mirizzi Syndrome

• Definition: Extrahepatic biliary obstruction due to an impacted stone in the cystic duct.

• Clinical Presentation: Jaundice, pain, fever.

• Associated Findings:

  • Intrahepatic duct dilatation, cystic duct stone, curved segmental stenosis of common hepatic duct.

Choledochal Cysts

• Definition: Anomalous junction of pancreatic duct into common bile duct causes reflux of pancreatic juices.

• Results in: Duct wall abnormalities, weakness, and outpouching.

• Clinical Findings: More common in children (<10 y/o), jaundice, and dilated ducts.

Caroli’s Disease

• Definition: Congenital segmental saccular cystic dilatation of intrahepatic bile ducts.

• Sonographic Findings:

  • Multiple cystic structures converging toward porta hepatis; may have sludge or calculi present.

Biliary Atresia

• Definition: Complete obstruction of extrahepatic biliary tree within the first three months of life.

• Consequences: Untreated leads to cirrhosis and death within the first year.

• Forms:

  1. Syndromic (10%): Associated with congenital anomalies.

  2. Non-syndromic (90%): Isolated anomaly.

Clinical Ultrasound Findings in Biliary Atresia

• Suspicion Indicators:

  • Shrunken gallbladder despite fasting.

  • Hyperechoic liver hilum (“triangular cord sign”).

  • Cyst at liver hilum (obliterated CBD).

Bile Duct Carcinoma (Cholangiocarcinoma)

• Characterization:

  • Primary cancer of biliary tree, originating in extrahepatic bile ducts.

• Symptoms:

  • Jaundice, unexplained weight loss, abdominal pain, elevated serum bilirubin.

• Sonography:

  • Dilated intrahepatic ducts that terminate abruptly at tumor mass; possible solid tumor in liver or ducts.

Klatskin Tumor

• Definition: Cholangiocarcinoma at the hepatic hilum.

• Impact: Causes intrahepatic but not extrahepatic biliary dilation, affecting the junction of the right and left hepatic duct.