Parasitic infection of the biliary tree is caused by liver flukes, namely Clonorchis sinensis and Opisthorchis viverrini. These flukes reside in the peripheral small bile ducts of the liver and produce chronic inflammation of the bile duct, bile duct dilatation, mechanical obstruction, and bile duct wall thickening. On imaging, peripheral small intrahepatic bile ducts are dilated, but the large bile ducts and extrahepatic bile ducts are not dilated or slightly dilated. There is no visible caused of obstruction. Sometimes, in heavy infection, adult flukes are demonstrated on sonography, CT or MR cholangiography as small intraluminal lesions. The flukes in the gallbladder may appear as floating, small objects on sonography. Chronic infection may result in cholangiocarcinoma of the liver parenchyma or along the bile ducts. Human infection of Fasciola hepatica, a cattle flukes, may occur inadvertently, and the flukes migrate in the liver (hepatic phase) and reside the bile ducts (biliary phase). Image findings in the hepatic phase present with multiple, small, clustered, necrotic cavities or abscesses in the peripheral parts of the liver, showing "tunnels and caves" sign, reflecting parasite migration in the liver parenchyma. In the biliary phase, the flukes are demonstrated in the intra- and extrahepatic bile ducts and the gallbladder as small intraluminal flat objects, sometimes moving spontaneously. Bile ducts are dilated.