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Secondary Common Bile Duct Stones. In most cases, common bile duct stones originally form in the gallbladder and pass into the common duct. They are then called secondary stones. Secondary choledocholithiasis occurs in about 10% of patients with gallstones.
Primary Common Bile Duct Stones. Less often, the stones form in the common duct itself (called primary stones). Primary common duct stones are usually of the brown pigment type and are more likely to cause infection than secondary common duct stones.

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