Choledochal cyst, or cystic dilatation of the common bile duct, presents as a cystic dilatation of the extrahepatic or intrahepatic bile ducts or both. The first anatomical abnormality was discovered by Vater and Ezler in 1723, the first clinical case was reported by Douglas in 1852, and the first systematic clinical and anatomical details were reported by Alonso-Lej in 1959. Most of the choledochal cysts are congenital developmental malformations. The causes are thought to be congenital dysplasia such as: 1. weakness of the bile duct wall, congenital defects in the supporting tissue of the duct wall, or ectopic pancreatic tissue that leaves the duct wall in a hypotonic state. 2. obstruction of the distal end of the common bile duct, resulting in increased pressure in the duct causing dilatation. The cause of obstruction can be congenital atresia; stenosis due to abnormal epithelial cell proliferation during bile duct development; spasm due to autonomic imbalance of the distal common bile duct; neuromuscular ataxia of the sphincter of Oddi; and obstruction caused by the angulation of the choledochoduodenal junction to produce a valve-like structure. Recent studies have found a close relationship between congenital common bile duct cysts and abnormal pancreaticobiliary collaterals. Most choledochal cysts have anomalous pancreatobiliary junction (APBJ), which is characterized by the confluence of the main pancreatic duct into the common bile duct more than 1 cm and further into the Vater’s jugular (P-B type) or the confluence of the common bile duct into the main pancreatic duct (B-P type). -Miyano and Yamataka found that more than 90% of patients with common bile duct cysts had pancreaticobiliary duct confluence abnormalities, and Komi et al. reported that 92.2% of common bile duct cysts were associated with pancreaticobiliary duct confluence abnormalities. In 52 cases of APBJ without congenital cystic dilatation of the bile duct, Chen Jong et al. had 32 cases of pancreatic duct injection into the common bile duct and 20 cases of common bile duct confluence into the pancreatic duct. Reflux of pancreatic juice into the common bile duct and activation of pancreatic zymogen under alkaline conditions can cause inflammation of the common bile duct and weakness of the duct wall. According to the results of Alonso-Lej’s study, choledochal cysts are generally divided into 3 types. (Caroli disease). Choledochal cysts are less common in Western countries and more common in Asia, with more reports from Japanese scholars, with Miyano and Yamataka reporting an incidence of 1 in 1,000 in Japan. Choledochal cysts and cholangiocarcinoma The main complication of choledochal cysts is obstruction of the distal bile duct and bilious enlargement, or even biliary cirrhosis, which can lead to portal hypertension. Portal hypertension can also occur due to direct compression of the portal vein by the cyst. Infection of the cyst can cause intrahepatic cholangitis, even multiple liver abscesses, and Escherichia coli sepsis. Rupture of the cyst, or leakage due to trial puncture, can cause diffuse peritonitis. In congenital choledochal cyst with pancreaticobiliary duct anomaly, the cancer rate increases significantly with age, and recently, in cases of pancreaticobiliary duct anomaly without combined choledochal cyst, the occurrence of biliary tract cancer is gradually increasing, and the site of its cancer is mostly the gallbladder. Some scholars observed the histology of the cyst wall of congenital common bile duct cyst and found that there is a structure similar to intestinal epithelial cells, i.e. epithelial metaplasia, which may be a pre-cancerous lesion. 2: Mutagenic substances in bile cause cancer theory: Some authors detected mutagenic substances in the bile of pancreaticobiliary duct coarctation abnormality and believed that mutagenic substances may be the factor that induces cancer. Therefore, early diagnosis and timely radical surgery are important.3: Bile acid carcinogenesis theory: The content of bile acid and deoxycholic acid, the metabolites of bile acid, increases significantly in the case of abnormal pancreaticobiliary co-flow and reflux of pancreatic juice to the bile duct. In addition, lithotriptic bile acids, which are normally present in very small amounts, are significantly increased in the bile of patients with abnormal pancreaticobiliary flow, and these bile acids have been shown to contribute to the production of mutagenicity in the bile. Therefore, early diagnosis and timely radical surgery are very important. Surgery for choledochal cysts and its relationship with cholangiocarcinoma Cancer of cysts can occur both in primary carcinoma of unoperated choledochal cysts and after surgery of cysts, so the choice of surgical procedure is related to the cancer of cysts. In principle, patients should be operated as soon as possible after diagnosis. Early surgery allows pancreaticobiliary diversion, which is important to prevent cyst cancer. The ideal surgery is to remove the cyst and reconstruct the biliary tract as early as possible to prevent mucosal malignancy caused by cirrhosis and recurrent biliary tract infections. At the same time, the younger the age, the less infected the cyst is, the less adherent the cyst wall is, the easier it is to peel off and the bleeding is relatively less. The current consensus on the treatment of choledochal cyst is to try to remove the choledochal cyst to eliminate the lesion, perform Roux-en-Y hepatic duct-jejunostomy to reconstruct the bile duct, perform biliopancreatic shunt, and prevent cancer. External cyst drainage is generally used only for temporary drainage and decompression in the event of acute septic biliary infection to facilitate elective surgery. Cystoduodenal drainage is generally only suitable for pediatric patients, and complex surgery is not appropriate for acute conditions, as an acute procedure, followed by complete surgery in the second stage. For Roux-en-Y jejunal cyst anastomosis alone with internal drainage, the lesion still exists because the diseased cyst wall is not removed, and the symptoms often recur after surgery. In addition, reflux of intestinal contents and retention of cyst contents are prone to complications such as infection, stones, anastomotic stenosis, etc., with a high incidence of complications, which affects the quality of postoperative survival of patients, and the high incidence of cancer after cyst internal drainage, which often requires reoperation, has been abandoned. -Y anastomosis has been the current standard. Pancreaticobiliary shunt and reconstruction of the biliary-intestinal channel do not necessarily require removal of the entire cyst, as the carcinoma originates from the mucosa, therefore, the prevention of carcinoma can be achieved by removing the mucosal layer. treatment options for types Iv and V (Caroli disease) are still controversial. For type IV, cystectomy and bile duct jejunostomy are currently advocated with good results, but regular postoperative follow-up review is required. the carcinoma rate of Caroli disease is 100 times higher than that of normal hepatic bile ducts and l0 times higher than that of hepatic bile duct cancer in the case of intrahepatic bile duct stones. For Caroli disease confined to one lobe of the liver, resection of one lobe or hemihepatectomy is performed. For Caroli disease with complex central pattern and recurrent infection, liver transplantation can be considered. Carcinoma can also occur in the biliary system, liver and pancreas outside the cyst. In 881 cases of common bile duct cyst reported by Kabayashi and Ishibashi in Japan, the carcinoma rate was 17.5%, of which bile duct cancer accounted for 57.8%, gallbladder cancer 40.3%, liver cancer 0.6%, and pancreatic cancer 1.3%. The average age of patients with primary carcinoma is 50 years old, the average age of patients with carcinoma after internal drainage of cyst is 35 years old, and the average age of patients at the time of internal drainage is 25 years old, so the average time from internal drainage to carcinoma is about 10 years. The primary carcinoma can be in the bile duct (53%) or the gallbladder (46%), while 85% of carcinomas occur in the residual cyst after internal arch drainage. After partial resection of the common bile duct cyst, the incidence of carcinoma in the remaining part of the cystic bile duct wall is much lower, although it can still occur. Recent reports in the literature have confirmed that the incidence of bile duct carcinoma increases with age in cases of surgically unresected cysts or after internal drainage. Peng Shuji et al. reported that 11 of 18 cases of cystic carcinoma were after internal drainage of cysts, which deserves attention.