An ultrasound examination shows dilated intrahepatic biliary channels with a small gall bladder. The most likely possibility is

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