This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
An ultrasound examination shows dilated intrahepatic biliary channels with a small gall bladder. The most likely possibility is 
Select and explain. 
A. Gall bladder stone, B. Pancreatic calculus, C. Common bile duct stone, D. Carcinoma of the head of the pancreas
C: Common bile duct stone
Answer: C: Common bile duct stone 
Explanation: In obstruction of the CBD due to a stone,distension of gallbladder seldom occurs.The organ is usually shrivelled.In obstruction from other causes ,distension of gallbladder is common by comparison. Reference:Bailey & Love's sho practise of surgery,25th edition,page no:1125