**1. Introduction**

Choledochal cysts (CCs) are congenital dilatations of extrahepatic and/or intrahepatic bile ducts defined by Vater and Ezler in 1723. It is a rare biliary entity with an estimated incidence of 1:100–150,000 live births in Western countries. In the Asian population, the incidence can be as high as 1:1000 live births. CC is primarily a childhood disease—up to 80% of patients are diagnosed before 10 years of age. The original classification, first described by Alanso-Lej and colleagues in 1959, was changed in 1977 by Todani and colleagues that classified the CCs as five types. In addition, isolated cystic dilatation of the cystic canal was identified subsequently and proposed as type VI, apart from the revised Todani classification. Although the etiology is controversial, the main elements in the natural historical emergence of the type I and type IV, which make up the majority of all types, have become clearer. A common symptom is nonspecific abdominal pain in older children. When the cyst is complicated, the diagnosis is delayed, the treatment becomes complex, and the results are affected. External drainage (ED), internal drainage (ID), total cyst excision (CE) + hepaticoduodenostomy (HD), and total CE + hepaticojejunostomy (HJ) were defined according to historical development of treatment. Resection is considered that is necessary to prevent further complications and long-term sequel.
