PATHOGENESIS OF CHOLEDOCHAL CYSTS

Choledochal cysts are thought to result from faulty budding of the primitive pancreatic duct. The outpouching of the ventral pancreatic bud originates from a more proximal position, closer to the liver. A long common channel that drains both the biliary and pancreatic systems result when the faulty ventral bud rotates and becomes the pancreatic duct. This anomalous arrangement of the pancreaticobiliary system is usually located far from the sphincter of Oddi (1).

The maximum pressure in the pancreatic duct exceeds that in the biliary system by two to three times (this results in pancreatic secretions that flow freely into the bile ducts if no sphincter is present. This reflux results in repeated bouts of cholangitis, inflammation and eventual fibrosis in the common bile duct. The destruction of the common bile duct wall in combination with the distal stenosis from scarring leads to dilatation of the common bile duct (1,2). Evidence supporting this theory includes the high levels of pancreatic amylase in choledochal cysts (3-5). Cylindric dilatation of the common bile duct has been induced in experimental models when exposed to pancreatic juice (5,6).

It is therefore conceivable that choledochal cysts are acquired from chronic pancreatic juice secretion due to a congenital anomalous pancreaticobiliary ductal union. The theory of malformation of the pancreaticobiliary ductal junction does not however explain the presence of choledochal cysts in the presence of normal pancreaticobiliary ductal union (7).

Obstruction of the common bile duct during fetal development may result in weakness of the choledochal wall that may result in a choledochal cyst. Obstruction may be due to congenital stenosis, abnormal valves, neuromuscular incoordination of the sphincter or agangliosis of the bile duct)

REFERENCES

1. Jona JZ, Babbitt DP, Starshak RJ et.al. Anatomic observations and etiologic and surgical considerations in choledochal cyst. J Pediatr Surg 1979;14:315-320.
2. Babbit DP, Starshak RJ, Clemett AR. Choledochal cyst: a concept of etiology. AJR 1973;119:57-62.
3. Okada A, Nakamura T, Higaki J et.al. Congenital dilatation of the bile duct in 100 instances and its relationship with anomalous junction. Surgery 1990;171:291-298.
4. Todani T, Watanabe Y, Fujii T et.al. Cyclindrical dilatation of the choledochus: a special type of bile dilatation. Surgery 1985;98:964-968.
5. Oguchi Y, Okada A, Nakamura T et.al. histopathologic studies of congenital dilatation of the bile duct as related to an anomalous junction of the pancreaticobiliary ductal systems: clinical and experimental studies. Surgery 1988;103:168-173.
6. Ohkawa H, Sawaguchi S, Yamazaki Y et.al. Experimental analysis of the cause of hyperamylasemia in choledochal dilatation with anomalous pancreaticobiliary ductal union. J Jpn Soc Pediatr Surg 1983;19:21-26.
7. Todani T, Watanabe Y, Fujii T et.al. Anomalous arrangement of the pancreaticobiliary ductal system in patients with a choledochal cyst. Am J Surg 1984;147:672-676.
8. Ito T, Ando H, Nagaya N et.al. Congenital dilatation of the common bile duct in children – the etiologic significance of the narrow segment distal to the dilated common bile duct. Z Kinderchir 1984;39:40-45.
9. Kusanoki M, Saltoh N, Yamamusa T et.al. Choledochal cysts and oligogangliosis in the narrow portion of the choledochos. Arch Surg 1988;124:984-986.