Congenital common bile duct cyst, also known as congenital cystic dilatation of the bile ducts, is a condition most commonly seen in children in Asia, but approximately 25% of congenital bile duct cysts develop in adulthood. With the development of biliary imaging, there is an increasing trend in the detection of bile duct cysts in adults. Because most of the symptoms of this disease are atypical or combined with hepatobiliary and pancreatic diseases, it often leads to misdiagnosis or delayed diagnosis. In recent years, with the in-depth study of the pathology, morphology and etiology of this disease, it has been found that in addition to cystic dilatation of the common bile duct, about half of the patients only present with a shuttle-shaped or cylindrical dilatation of the common bile duct, rather than a giant cyst. In addition to extrahepatic dilatation of the common bile duct, about 1/4 of the cases also had a combination of intrahepatic bile ducts with pyknotic or even small cystic dilatation. Therefore, it has been widely accepted at home and abroad that this condition is called congenital bile duct dilatation.
The cause of congenital cystic dilatation of the bile ducts is a surgical biliary disease with biliary stasis, and its etiology has not yet been determined. There are several theories as follows:
1, pancreatic and bile duct confluence abnormalities: 80%~100% of bile duct cysts are accompanied by pancreaticobiliary duct confluence abnormalities. The so-called pancreaticobiliary duct confluence abnormality refers to the anatomical confluence of the pancreaticobiliary ducts outside the duodenal wall before the common opening in the duodenal papilla, forming an excessively long common channel, and the functional failure to control the confluence due to the action of the Oddi sphincter in the duodenal papilla, resulting in the mixing and reflux of pancreatic juice and bile, which eventually leads to a series of pathological changes in the biliary tract and pancreas.
2. Embryological theory: The formation of extrahepatic bile duct system is mostly in the process of bile duct development during the embryonic period from the 5th to the 7th week of fetal life, when the bile duct epithelium is vacuolated, the local duct wall is weak, and its epithelial proliferation is abnormal resulting in uneven epithelial proliferation rate in all parts of the bile duct, narrowing of the lower section into the duodenum, increasing the bile duct pressure, and dilatation of the upper bile duct at the dysplasia.
3, biliary nerve dysplasia theory: congenital bile duct cyst terminal stenosis segment nerve distribution abnormally reduced, pancreaticobiliary duct merging abnormalities may coexist with cyst terminal nerve development abnormalities. Due to the abnormal nerve development, spastic stenosis of the distal bile duct occurs, and the pressure in the pancreatic duct is higher than the pressure in the bile duct, which causes the pancreatic juice to flow back into the bile duct, persisting and damaging the bile duct wall, and the two act together to form a bile duct cyst.
4, viral infection theory: it is believed that bile duct dilatation may be caused by cytomegalic inclusion body virus (CMV) infection. Viral infection causes the liver cells, capillary bile duct epithelial cells to undergo giant cell degeneration, cell damage and lead to bile duct wall weakness and dilatation. Cytomegalic inclusion virus has also been detected in the liver of congenital bile duct dilatation cases in China. However, as the understanding of the disease has advanced, most people believe that it may be a viral infection based on the original disease, and is a combination of the presence of a viral infection pathological changes.
The typing scholars at home and abroad have proposed various typing criteria from different perspectives. In terms of choledochal cysts, most scholars prefer the Alonson-Lej classification, namely type I cystic dilatation of the common bile duct, type II diverticulum of the common bile duct, and type III terminal cyst of the common bile duct. The current widely adopted criteria classify bile duct cysts into type V, i.e., type I-III is the same as Alonson-Lej classification, type IV-A is intrahepatic and extrahepatic bile duct multiple cysts, type IV-B is extrahepatic bile duct multiple cysts, and type V is intrahepatic bile duct single or multiple cysts (Caroli disease).
The incidence of congenital bile duct cysts is more likely to occur in women, accounting for about 62%~74%. (Type I accounts for about 90%, type II accounts for about 2%, and type III accounts for about 1.5%.
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IV. Typical clinical manifestations.
1, abdominal pain: mostly confined to the epigastrium, right upper abdomen or around the umbilicus, the nature of pain is more colic, but also can be manifested as continuous or intermittent dull pain, distension or pulling pain, sometimes high fat or excess diet can induce the occurrence of abdominal pain. The manifestations of abdominal pain in young children are often misdiagnosed because they cannot be told. Infants often have abdominal pain in a kneeling position with the head and shoulders down, which seems to be a reference for the manifestation of abdominal pain. Some children have recurrent episodes of abdominal pain that last for months or even years, and the pain attacks are often accompanied by jaundice and can be accompanied by nausea, vomiting, anorexia and other gastrointestinal symptoms. According to statistics, cases with abdominal pain symptoms account for about 60-80% of all cases.
2.Mass: Mostly smooth masses are palpated in the right upper abdomen with cystic feeling, the upper boundary is mostly covered by the liver edge, and there may be light and severe tenderness. Some of the cysts have flap-like folds at the lower end of the common bile duct, which acts as an activating flap, and the cysts become smaller when the contents are discharged, and the jaundice gradually subsides. It has a high reference value for the diagnosis of this disease.
3, jaundice: intermittent jaundice for its characteristics, the appearance of jaundice interval length varies, severe jaundice can be accompanied by skin itching, general discomfort. The appearance and deepening of jaundice indicates poor bile drainage due to distal obstruction of the common bile duct. When the inflammation decreases and the bile is drained freely, the jaundice may be relieved or subside. In some children, when the jaundice worsens, the stool becomes lighter or even white clay-like, and the urine is dark yellow. In addition to the main symptoms mentioned above, there may be fever when combined with infection in the cyst, and the temperature may be as high as 38-39 ℃, and nausea and vomiting may be caused by inflammation.
V. Diagnosis
1.Clinical diagnosis
The clinical proportion of those who have abdominal pain, jaundice and mass is not high, and most cases have combined hepatobiliary and pancreatic system diseases, and the rate of congenital cystic dilatation of bile duct is 2.5%-15%.
With the improvement of imaging diagnosis, the diagnosis rate of congenital cystic dilatation of bile duct has reached 70%~90%, and it is easier to diagnose in children than in adults.
(1) Ultrasound: the diagnosis can be initially obtained. It shows a well-defined hypoechoic area under the liver, and can identify the degree and extent of intrahepatic bile duct dilatation and whether it is combined with bile duct stones. This method is non-invasive, inexpensive, and easy to promote, and should be preferred.
(2) Endoscopic ultrasound (EUS): its probe can be placed in the stomach through the endoscope closer to the lesion, which has a unique role in the diagnosis of bile duct cysts.
(3) X-ray examination: suitable for larger cysts, a soft tissue mass with smooth edges and uniform density is seen in the right upper abdomen, and the stomach and colon are pushed, the gastric sinus is pushed to the left, the duodenal segment is pushed to the right, and the duodenal box is enlarged, but it is more difficult to diagnose cystic dilatation in the cloacal form with ordinary X-ray examination.
(4) CT examination: It can clarify the degree of dilatation of the common bile duct, its location, the degree of distal stenosis of the common bile duct, the presence of intrahepatic bile duct dilatation, the shape and location of the dilatation, etc., which can help in the selection of the operation.
(5) Magnetic resonance pancreaticobiliary imaging (MRCP): It is a high-tech non-invasive imaging technique that was maturely applied to clinical practice in the 1990s. High-quality MRI can obtain a clear image of the pancreaticobiliary duct and can clearly determine whether there is a combined pancreaticobiliary flow abnormality. However, sometimes due to technical problems of the operator or poor cooperation of the patient, satisfactory images cannot be obtained.
(6) Retrograde cholangiopancreatography (ERCP): It is the most effective examination method for understanding the bile duct, pancreatic duct and pancreaticobiliary duct union, and it can provide an important objective basis for the presence or absence of pancreaticobiliary coarctation abnormalities and their types. The diagnostic effect can be better than that of PTC.
(7) Percutaneous hepatic cholangiography (PTC) examination: it can show the site of cystic dilatation of intrahepatic bile ducts and the degree of stenosis of distal and proximal bile ducts. To understand whether there are abnormal merging of pancreaticobiliary ducts and pathological changes of distal pancreaticobiliary ducts. Bile can be taken for bacteriological examination. This method is best used when ERCP examination fails.
(8) Intraoperative cholangiography:
Intraoperative cholangiography is necessary in cases where preoperative ERCP has failed or MRCP is not clear. It can provide a detailed understanding of the pathology of the intrahepatic bile duct and the abnormalities of the distal bile duct and pancreaticobiliary flow. It is very important to guide the selection of the correct surgical method.
Sixth, congenital bile duct dilatation carcinogenesis
1. The doctrine of pancreatic reflux destruction: Since the secretory pressure of pancreatic juice is significantly higher than the secretory pressure of bile, patients with abnormal pancreaticobiliary coflow often experience reflux of pancreatic juice to the bile duct. When pancreatic juice enters the bile duct, many kinds of pancreatic enzymes will be activated in the bile duct, and the activated pancreatic enzymes will have destructive effects on the bile duct mucosa and cause cancer through the process of destruction → repair → destruction of the bile duct mucosa.
2. Bile acid carcinogenesis theory: The chemical structures of bile acid metabolites, bile acid and deoxycholic acid, are similar to the structure of a known carcinogenic substance, and the metabolites of two bile acids may denature and become such carcinogenic substances. The levels of these two bile acids are significantly increased in the case of abnormal pancreaticobiliary co-flow and reflux of pancreatic juice to the bile duct. In addition, the amount of lithotriptic acid, which is normally minimal, is significantly increased in the bile of patients with abnormal pancreaticobiliary flow, and this bile acid has been shown to contribute to the production of mutagenicity in the bile.
3. The theory of carcinogenicity of mutagenic substances in bile: Due to the presence of abnormal pancreaticobiliary collaterals, pancreatic juice merges with bile and the pancreatic juice in the bile duct can cause the carcinogenic substances detoxified by the liver and conjugated and discharged to the bile duct with bile to regain their carcinogenicity. In clinical work, patients with combined biliary dilatation have bile depression and prolonged retention in the bile duct. Therefore, the incidence of biliary tract cancer is much higher in patients with abnormal pancreaticobiliary flow than in normal subjects.