This classification classifies the choledochal cysts into 5 cathegories.
Type V, which is not shown above is Caroli disease.
We now know, that Caroli is a different disease.
Type I is a true choledichal cyst with focal dilatation of the extrahepatic duct.
This is the most frequent type (90-95% of the cases).
Type IV is also a true choledichal cyst with dilatation of the entire extrahepatic duct with involvement of portions of the intrahepatic ducts.
The intrahepatic ducts taper normally to the periphery, indicating that there is no obstruction.
Type II and III are extremely rare and it is debatable whether or not these are true choledochal cysts.
Type II is a diverticulum of the extrahepatic duct and many believe that this entity is not related to an anomalous pancreatico-biliary junction.
Type III is a choledochocele, where there is dilatation of the distal part of the bile duct.