Congenital cyst of common bile duct: an unusual cause of obstructive jaundice. Congenital cysts, sometimes referred to as nonparasitic biliary cysts, are not unusual findings in the liver parenchyma, but they have not been previously described in the common bile duct. This clinical report describes a 41-year-old woman with obstructive jaundice that was caused by congenital cysts. The patient had obstruction of the middle portion of the common bile duct; therefore the major differential diagnostic considerations were cholangiocarcinoma, cancer of the pancreas, or true biliary cysts. Congenital cysts, retention cysts, and neoplastic cysts cannot be differentiated from other true cysts preoperatively. Diagnosis can only be established by microscopic examination after surgical excision. 