Duplication of the common bile duct is an extremely rare condition. The presence of double bile ducts is a normal step in human early embryogenesis. The definite lumen of the bile tree is developed by epithelial proliferation and vacuolization. As the vacuoles coalesce, they will initially create two parallel channels, which will gradually recede to form an isolated common anatomical structure of the common bile duct [4]. Regression failure of the double biliary system is considered to be the mechanism of type I anomaly [5].Chance elongation and early subdivision of the primitive hepatic furrow may be responsible for the other types of DCBD [6].The latest classification system of the DCBD proposed by Choi et al. [7] (2007) based on morphology which did not take into account of the aberrant CBD exits. They described five subtypes involving seven variants (Fig. 3). Since then, three new variants of double common bile duct were reported consecutively, however, none of these were classified into classification system [8–11] (Fig. 4). Our case is a new variant of diaphragmatic common bile duct duplication type I.The reason that why our case was classified as type I was that it was confirmed intraoperatively that there was a septum in common bile duct rather than two separate common bile ducts. The septum of original type I was located in the common bile duct. In our case, the septum in the common bile duct extended to the junction of the left and right hepatic ducts. The above-mentioned variants need a comprehensive classification to encompass these newly discovered variants. Thus, our classification system is as follows (Fig. 5): Type I, Partially (a) or completely (b) septum within the lumen; Type II, the distal bile duct bifurcates to two independent drainages; Type III, double biliary drainage without any communication (a), with intrahepatic communication (b); Type IV, double biliary drainage with extrahepatic communicating channels; TypeV, duplicated commen bile ducts join as a single biliary drainage channel,the gallbladder is attached to the repeated biliary ducts or Left or right hepatic duct (a), the gallbladder is connected to the common bile duct before or after separation(b). Our classification is including all types of common bile duct duplication reported in the present literature. Because of the location of the gallbladder junction and the location of the traffic between the repeated biliary ducts, our classification may contain additional variations not found.

The proportion of type I DCBD is higher in the Chinese population than any other types [12]. DCBD is related to anomalous biliopancreatic junction, congenital choledochal cysts, and biliary atresia and can give rise to complications such as choledocholithiasis, cholangitis, pancreatitis, and malignancies [13]. Its main symptoms include upper abdominal pain, nausea or vomiting, pain in the upper right quadrant, heartburn, fever and jaundice. When clinical manifestations of these hepatobiliary problems occur, the primary imaging approach is usually ultrasound examination in children. Ultrasound examination can clearly show and diagnose choledochal dilatation or biliary tract calculi, but may not show subtle structural abnormalities. In our case, the initial ultrasound examination did not observe repeated common bile duct [14]. The current gold standard for diagnosing biliary tract diseases is endoscopic retrocholangiopancreatography (ERCP), an invasive technique in which contrast agents are injected directly into the gallbladder or bile ducts, which can lead to serious complications, including pancreatitis and duodenal perforation. In addition to ultrasound, MRCP and CT are the most commonly used imaging methods. DCBD was shown by Sang et al. [15] through the minimum density projection using the post-processing technology of multi-slice spiral CT. However, CT cannot be used as a routine preoperative examination for biliary tract diseases in children due to radiation problems. MRCP is a non—invasive examination without injecting contrast agent and without radiation injury, thus is usually the first choice for screening the biliary tract diseases in children requiring surgery. Examination of biliary trees by MRCP may be useful in the diagnosis of other associated congenital anomalies and pathological changes.

In summary, we report a rare case of duplication of the common bile duct combined with congenital biliary dilatation. We complement and adjust the classification of common bile duct duplication which includes all of variations been reported. The primary imaging approach is usually ultrasound. MRCP is usually the first choice for screening duplication of the common bile duct in children requiring surgery.