Teaching Case

A 3-year female child with on/off chronic abdominal pain from 6 months of age. Initially bilious, however, later nonbilious vomiting, was reported by child's mother. Child was afebrile, vitals were within normal range and systemic examination was unremarkable. Workup showed a fourfold increase in amylase level (552 IU/L) and significantly high lipase level (2120 IU/L) with slightly raised alkaline phosphatase level.

Ultrasound showed dilated bile duct and intrahepatic biliary channels. Fusiform dilatation of intra and extrahepatic segments of common bile duct. No intraluminal filling defect was seen to suggest choledocholithiasis. The liver showed smooth hepatic echotexture with regular margins without any focal lesion. Portal vein was unremarkable. Normally distended gall bladder was seen without an intraluminal calculus.

MRCP revealed a dilated, fusiform common bile duct with a segment of narrowing at its distal part measuring 9 mm in length (possibly a stricture). Abnormal union of distal narrowed CBD with pancreatic duct outside duodenal wall formed a long, relatively dilated common channel, measured 19 mm in length and 4.6 mm in calibre. Pancreas appeared normal without any evidence of pancreatic divisum. Laboratory workup and imaging were consistent with the clinical impression of Type C pancreaticobiliary malformation (The Japanese Study Group on Pancreaticobiliary Maljunction 2015) with an associated type 1-C choledochal cyst (Todani classification).

Pancreaticobiliary maljunction (PBM), synonymously termed as "anomalous arrangement of pancreaticobiliary duct" or "anomalous union of biliopancreatic ducts", is an abnormal convergence of pancreatic duct and common bile duct outside duodenal wall beyond the influence of sphincter of Oddi. It forms a long-shared channel, about 8-12 mm in length and leads to two-way regurgitation [1, 2]. As hydrostatic pressure within pancreatic duct is typically greater than CBD, backflow of pancreatic juice into bile duct occurs consequently raising the levels of pancreatic enzymes within bile. Persistence of refluxed pancreatic juice injures biliary tract epithelium and heightens the risk of biliary carcinogenesis, and can also be responsible for cholangitis, pancreatitis, etc. [3-5]. Abdominal pain, vomiting, jaundice, and fever are the primary symptoms of PBM [6]. This congenital anomaly is rare, with an incidence of 1 in 1000 reported in the Asian population, which is 100 to 1000 times higher than the reported incidence in other parts of the world [8]. As reported in some multicenter European studies, the association of pancreaticobiliary maljunction with choledochal cysts has a prevalence of 72.2% [10]. However, it is considered to be an independent disease entity from choledochal cyst [7].

The Japanese Study Group on Pancreaticobiliary Maljunction in 2015 suggested a new classification that categorizes PBM into four types: (a) stenotic type, where the distal common bile duct joins the common channel with a constriction; (b) non-stenotic type, where the distal common bile duct joins the common channel without any constriction; (c) dilated channel type, where the common channel is expanded; (d) complex type, where the PBJ has developed in a complicated configuration [9].

Early detection and appropriate treatment are crucial for patients with PBM and the effectiveness of both largely depends on the use of imaging techniques. Ultrasonography is a good screening tool. The emergence of diagnostic imaging techniques such as multidetector CT and MR cholangiopancreatography has bestowed upon radiologists a crucial responsibility in detecting PBM and its associated complications. Although infrequent in non-Asian populations, radiologists must be knowledgeable of PBM [8].

Treatment involves complete removal of extrahepatic bile duct and gallbladder, succeeded by a hepaticojejunostomy, Roux-en-Y, or end-to-side hepaticoduodenostomy. Early surgical intervention ensures a positive outcome while minimizing the occurrence of complications. However, follow-up care is also essential for detecting any potential malignancies in the biliary tract, especially in patients who experience complications following surgery [1].

Outcome

Our patient underwent exploratory laparotomy confirming intraoperative findings of type IC choledochal cyst with pancreaticobiliary malunion, followed by choledochal cyst excision + hepaticojejunostomy and small bowel anastomosis to prevent symptoms and also to prevent risk of complications, especially biliary cancer.

Take Home Message

PBM is diagnosed on the basis of imaging or on autopsy. Given its association with biliary cancer, it is imperative for us as radiologists to remain vigilant and exercise great care when interpreting imaging studies such as MRCPs. By doing so, we can help prevent a rise in the incidence of this condition and associated malignancies.

All patient data have been completely anonymised throughout the entire manuscript and related files.