This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hepatobiliary radiology, Subject name: Radiology
[{'content': 'Linear filling defect on ERCP is characteristic of which of the following : \nSelect and explain. \nA. Bile duct stone, B. Pancreatic duct stone, C. Worm in biliary tree, D. Stricture', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Linear filling defect in main CBD is a characteristic feature of BILIARY ASCARIASIS. ERCP is the gold standard but an invasive method. It is used also in the extraction of CBD worms. The worms appear as a hypointense structure within the hyperintense CBD giving linear filling defect on MRCP/ERCP', 'role': 'assistant'}]