Choledochal cyst is a common congenital biliary disorder, most of them are diagnosed before the age of 10 years, but some of them are delayed until adulthood until the diagnosis is made, which is called adult congenital choledochal cyst, and it is more common in females. Etiology: Currently, the main theory is that the cause is abnormal pancreaticobiliary syncytium, i.e., the choledochus and the pancreatic duct form a long pancreaticobiliary syncytium common duct, and pancreatic fluid and bile can be mixed in the common duct. the Oddi’s sphincter leads to high pressure at the distal end of the common duct, which will cause the mixture of pancreatic and bile to reflux to the choledochus and the pancreatic duct; pancreatic fluid refluxes into the biliary duct, and the pancreatic enzymes, elastase, and collagenase inside the duct will lead to damage to the wall of the biliary duct, and the biliary tract will become damaged. can cause damage to the wall of the bile duct, making it weak and dilated. Types: Cysts are divided into five types: Type I, dilated common bile duct, including cystic dilatation and spindle-shaped dilatation; Type II, diverticulum-shaped outward projection of the common bile duct; Type III, cystic dilatation of the common bile duct to the duodenum; Type IV, dilatation of the intrahepatic and extrahepatic common bile ducts at the same time; Type V, dilatation of the intrahepatic bile ducts, the extrahepatic bile ducts are normal, also known as Caroli’s disease. However, some scholars believe that this classification method has limitations and is not sufficient to reflect the pathologic features of this malformation and guide treatment. However, this is the typology of most surgical textbooks, and it is also the typology with more clinical applications. Clinical manifestations: The clinical manifestations of choledochal cyst are mostly: abdominal mass, jaundice, and abdominal pain. The probability of the combination of the three at the same time is not high, and most often manifests one of them, and a large proportion of adults are also found during physical examination. Diagnosis: Abdominal ultrasound is the most convenient, inexpensive, and commonly used means of diagnosing choledochal cysts. ercp and magnetic resonance imaging (MRCP) are the most accurate tests for visualizing the lesion. ercp is traumatizing and has largely been replaced by magnetic resonance imaging (MRCP). Enhanced CT helps to see if there is cancer inside the cyst. Treatment: Choledochal cysts have a high rate of cancer, with reports of up to 17% and our finding of 10%. Therefore, in order to prevent cancer, surgery should be performed as soon as it is detected, and the treatment is now well recognized: cystectomy with hepaticojejunal Roux-Y anastomosis is the standard procedure for the radical treatment of choledochal cysts. Cystic dilatation of the intrahepatic bile ducts is limited to one lobe of the liver, or half of the liver can be hepatectomized. Diffuse intrahepatic choledochal cystic dilatation is more complicated to treat, especially when combined with diffuse stones, and liver transplantation is an option if liver function continues to deteriorate. Example: preoperative CT in a patient with choledochal cystic carcinoma undergoing pancreatic head duodenectomy: