This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Surgery
[{'content': 'Most faceted gallstones are formed in the \nSelect and explain. \nA. Liver, B. Gall bladder, C. Common in bile duct, D. Spiral valves of Heister', 'role': 'user'}, {'content': 'Answer: B \nExplanation: (B) Gall bladder # Pigment stones are seen in patients with haemolysis in which bilirubin production is increased.> Examples are hereditary spherocytosis, sickle cell anaemia, thalassaemia, malaria and mechanical destruction of red cells by prosthetic heart valves.> Pigment stones are found in the ducts of patients with benign and malignant bile duct strictures.> Pigment stones in Oriental countries are associated with infestations of the biliary tree by Clonorchis sinensis and Ascaris lumbricoides.> Escherichia coli is often found in the bile of these patients. This bacterium produces the enzyme t3-glucuronidase which converts the bilirubin into its unconjugated insoluble form.> These stones are often present throughout the biliary tree including the intrahepatic ducts.', 'role': 'assistant'}]