Intrahepatic biliary dilatation with a normal common bile duct (CBD) is typically caused by obstruction located at or above the level of the hepatic duct confluence. A tumor at the porta hepatis, such as cholangiocarcinoma (Klatskin tumor), is a classic cause of this pattern. The porta hepatis is the site where the right and left hepatic ducts join to form the common hepatic duct. A mass at this location can obstruct the intrahepatic ducts while leaving the distal CBD unaffected and of normal caliber.
By contrast:
Portal vein thrombus (A) affects vascular flow but does not directly obstruct bile ducts.
Choledocholithiasis (C) obstructs the CBD, typically resulting in both intrahepatic and extrahepatic duct dilatation.
Acute pancreatitis (D) may cause distal CBD compression if there is associated inflammation or pseudocyst formation, but typically results in extrahepatic duct dilatation rather than isolated intrahepatic dilation.
Reference Extracts:
Rumack CM, Wilson SR, Charboneau JW, Levine D. Diagnostic Ultrasound, 5th ed. Elsevier, 2017. Chapter: Biliary Tract: “Klatskin tumors cause proximal (intrahepatic) biliary dilatation while the distal bile duct remains normal in caliber.”
Gore RM, Levine MS. Textbook of Gastrointestinal Radiology, 4th ed. Saunders, 2015.
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