I. Overview of congenital common bile duct cyst Congenital common bile duct cyst, also known as congenital cystic dilatation of the common bile duct, is one of the most common congenital biliary malformations in clinical practice. The lesion is mainly a congenital malformation in which a part of the common bile duct is cystically or syrinely dilated, sometimes accompanied by dilatation of the intrahepatic bile duct. Like other congenital biliary anomalies, the incidence of this condition is significantly higher in Asian Orientals than in European and American Whites. The incidence is higher in females than in males, accounting for approximately 60-80% of the total incidence. It can be seen at all ages, but the cystic form is mostly diagnosed and treated in children under 10 years of age, while the cloacal form is more often delayed until adulthood. Currently, with the introduction of prenatal screening, cystic choledochal cysts can be diagnosed in the fetus. Currently, there are more than 40 cases diagnosed in our hospital every year. The specific cause of its pathogenesis is still not fully understood, but most scholars believe that it is a congenital disease. It is believed that it may be related to the following theories: 1) embryonic malformation of the biliary tract; 2) terminal obstruction of the common bile duct; 3) the theory of viral infection; 4) distal nerve and muscle dysplasia of the common bile duct; 5) hereditary factors; 6) the theory of abnormal pathogenesis of the pancreaticobiliary commissure; 7) some scholars believe that its etiology may be due to congenital developmental malformations caused by various factors. The harm of common bile duct cyst 1, biliary tract infection Due to the abnormal development of common bile duct, the distal obstruction of bile duct, resulting in poor excretion, resulting in the accumulation of stagnation in the cyst, causing biliary tract infection. Severe cases can be aggravated and cause purulent cholangitis, which can be life-threatening. 2. biliary stones Causes siltation in the bile ducts, leading to an increase in bile concentration, causing bile salt deposits and the formation of biliary stones. It can aggravate biliary tract infection and biliary tract obstruction. 3.Biliary perforation Biliary obstruction can lead to bile stasis, which causes the pressure in the cyst to rise continuously, and when it reaches a certain level it can lead to the perforation of that kind of philtrum, causing cholestatic peritonitis and infectious shock. 4.Liver lesions Due to repeated inflammation and infection of common bile duct or intrahepatic bile duct, bile retention caused by different degrees of obstruction of common bile duct, all these lesions can cause liver damage. In early inflammatory cell infiltration in the portal system may be combined with mild liver fibrosis, and in infants when biliary obstruction is severe, there may even be complications such as biliary atresia-like biliary cirrhosis and portal hypertension. 5, bleeding tendency The human body needs very little vitamin K, but it is a trace element to maintain normal blood coagulation, and the absorption of fat-soluble vitamin K needs the assistance of bile, the amount of bile discharged into the digestive tract of patients with choledochal cysts is low, which inevitably affects the absorption of vitamin K, thus leading to coagulation dysfunction and causing a tendency to bleeding. 6, biliary tract carcinoma Recent studies have found that biliary tract carcinoma has become the most serious complication of congenital bile duct dilatation. A lot of literature reports that the incidence of biliary tract cancer in congenital bile duct dilatation is 25-40 times higher than that of normal population. The rate of biliary tract carcinoma also increases dramatically with age. Clinical manifestations of choledochal cyst 1. Abdominal pain is mostly confined to the upper abdomen, right upper abdomen or around the umbilicus. The nature of pain is mostly colic, but it can also be persistent or intermittent dull pain, swelling pain or pulling pain. Sometimes abdominal pain can be triggered by a high-fat or high volume diet. The manifestations of abdominal pain in young children are often misdiagnosed because they do not complain. In some cases, the abdominal pain is recurrent and lasts for months or even years, and the pain attacks are often accompanied by jaundice and can be accompanied by gastrointestinal symptoms such as nausea, vomiting and anorexia. According to statistics, those with abdominal pain account for 60-80%. Some have sudden acute abdominal pain with symptoms of peritoneal irritation, common perforation of the common bile duct and secondary peritonitis. 2, mass Mostly in the right upper abdomen or the right side of the abdomen there is a cystic smooth mass, the upper boundary is mostly covered by the liver edge, the size varies. There may be tenderness of varying severity. Some of the cysts have flap-like folds at the lower end of the common bile duct, which acts as an activating flap. When the contents are drained, the cysts become smaller and jaundice is seen to subside. In the case of cystic duct dilatation, no abdominal mass is palpable. 3, jaundice Intermittent jaundice is its characteristic, and most cases have this symptom. Severe jaundice may be accompanied by itching of the skin and general discomfort. The appearance and deepening of jaundice indicates poor bile drainage due to obstruction of the distal common bile duct. It may be due to combined intracapsular infection or pancreatic reflux. When the inflammation is reduced and the bile drains freely, the jaundice may resolve or subside. When jaundice worsens in some children, the color of the stool becomes lighter or even white clay, while the urine is dark yellow. In addition to the three main symptoms, there may be fever when combined with infection in the cyst, and the temperature may be as high as 38-39 ℃, and gastrointestinal symptoms such as nausea and vomiting may be caused by inflammation. If the disease is prolonged or combined with jaundice, the child may have low synthesis of clotting factors due to impaired absorption of fat-soluble vitamin K. The child may show signs of easy bleeding.