The disease concept of CBD and classification according to morphological features was first described by Alonso-Lej et al. in 1959 [6]. It is well known that CBD merges with PBM in all cases. PBM is a congenital anomaly defined as a junction of the pancreatic and biliary ducts located outside of the duodenal wall that usually forms a markedly long common channel [2, 3]. As the action of the sphincter of Oddi does not functionally affect this union, two-way regurgitation (biliopancreatic and pancreatobiliary reflux) occurs, resulting in various pathological conditions in the biliary tract and pancreas [7, 8]. PBM, particularly in Asian patients, is a well-known risk factor for the development of carcinoma in the biliary tract [9]. According to a report by Todani et al. [10], the mean patient age for carcinoma arising in a choledochal cyst is 37 years (range, 15–73 years). Therefore, advanced biliary tract carcinoma in teenage patients is relatively uncommon.

A MEDLINE literature search of English language articles revealed only six cases of biliary tract carcinoma in patients with PBM or CBD younger than 20 years (Table 2) [11–16]. Of these six patients, half were male and the most common PBM subtype was C-P, in which the common bile duct joins the major pancreatic duct. According to the classification of Todani [17], two patients had type 1a disease and two had type 4-A disease. The most common histological type of cancer was adenocarcinoma, and four cases underwent complete tumor resection of the choledochal cyst.

In the present case, the bile amylase level in the common bile duct was 54,722 IU/l, so chronic inflammation leading to malignant change was observed. This high amylase level in the choledochal cyst suggested a free reflux of pancreatic juice into the biliary system that might have caused chronic inflammation in the choledochal cyst [18]. The carcinogenesis of CBD coexisting with PBM is considered to involve the hyperplasia-dysplasia-carcinoma sequence provoked by chronic inflammation resulting from a reflux of pancreatic juices into the biliary tract [4, 5]. Strong cytotoxic substances are produced when phospholipase A2 in the pancreatic juice mixes with bile, which have been recognized both clinically and experimentally to be injurious to cell membranes. Moreover, the subsequent chronic inflammation provokes high proliferative activity in the mucosal epithelia, finally resulting in CBD in PBM patients [19].

Once a diagnosis of CBD is made, early radical surgery for CBD combined with thorough intraoperative histopathologic examinations may be necessary, irrespective of the patient’s age. A preoperative diagnosis of bile duct carcinoma in CBD is sometimes difficult to establish [16]. In our case, the enhanced huge tumor in the dilated choledochus on CT was an important clue for the diagnosis of malignancy in CBD. The carcinoma spread to the level of the bile duct in the pancreas; therefore, after additional excision of the perihilar bile duct, SSPPD was performed. The surgical procedure should be modified based on the spread of the carcinoma because radical resection appears to be the only chance of cure in such cases.