anomalous pancreaticobiliary junction

An anomalous pancreaticobiliary junction, also known as pancreaticobiliary maljunction, describes the abnormal junction of the pancreatic duct and common bile duct that occurs outside the duodenal wall to form a long common channel (>15 mm).

Epidemiology

It is more common in Asia and eastern countries. The estimated prevalence in Asia is 100 to 1000 times higher than in other parts of the world . It is more common in females (F:M=3:1) .

It can be divided into 2 types:

• with biliary dilatation: accounts for 50% of cases, 50% diagnosed in children, often associated with stricture of the hilar duct and tends to have a higher incidence of symptoms 
• without biliary dilatation: the main symptom is abdominal pain. It is more difficult to diagnose as there is no biliary dilatation 

Associations

• choledochal cyst: the vast majority of patients with Todani type Ia, Ic, and IVa choledochal cysts, in which dilatation involves principally the main bile duct, have an anomalous pancreaticobiliary junction
• bile duct stricture: affecting the distal duct or hilar duct
• pancreatic anomalies: annular pancreas or pancreas divisum, is rare and seen in the complex type
• synchronous biliary cancer: rare with increased incidence on coexistence with biliary dilatation, especially Todani type I

Clinical presentation

Abdominal pain, vomiting, jaundice, and fever. Abdominal pain occurs regardless of age or the presence of biliary dilatation .

Pathology

The origin of a long common channel might be formed embryologically with adhesion of the ventral pancreatic duct and the terminal portion of the bile duct . It is divided into anomalous pancreaticobiliary junction with biliary dilatation (77%) and without biliary dilatation (23%) .

The anomalous pancreaticobiliary junction makes biliary drainage not under the control of sphincter of Oddi, resulting in pancreatic juice reflux into the biliary tract that injures the biliary epithelium .

Classification

The Japanese Study Group on Pancreaticobiliary Maljunction (JSPBM) proposed the following classification in 2015 :

• type A (stenotic type): dilatation of the common bile duct upstream of a stenotic segment of the distal common bile duct, which joins the common channel
• type B (non‐stenotic type): nonstenotic distal common bile duct smoothly joins the common channel; no localized dilatation of the common channel
• type C (dilated channel type): narrow distal common bile duct joins dilated common channel
• type D (complex type): complex maljunction associated with annular pancreas, pancreas divisum, or other complicated duct systems

Radiographic features

ERCP

An intrabiliary amylase level more than 8000 UI/L within the bile duct and gallbladder obtained endoscopically (ERCP) or percutaneously suggests reflux of pancreatic juice through an anomalous pancreaticobiliary junction and shows a positive predictive value and a specificity of more than 90 % .

In patients with a short common channel, direct cholangiography (e.g ERCP) can be effective in the assessment of pancreaticobiliary junction incompetence.

Ultrasound

It has a limited role in diagnosis, but a useful noninvasive tool for screening. Careful measurement of the common bile duct and compare it with the normal limits for age helps early detection. Detection of a dilated common bile duct may be the first clue to suspect pancreaticobiliary maljunction with biliary dilatation. In this case, further MRCP is recommended for biliary junction anatomy. It is also associated with gallbladder wall thickening, however non-specific.

The visualization of pancreaticobiliary junction outside the duodenal wall can be detected at endoscopic ultrasound. It is also helpful in screening and surveillance of biliary cancer after diagnosis of pancreaticobiliary maljunction.

CT/MRI

• a common channel length of >8 mm
• an abnormal union between the pancreatic and bile ducts
• pancreaticobiliary junction outside the duodenal wall, 
• common bile duct dilatation is suggestive of pancreaticobiliary maljunction with biliary dilatation

MRCP is the gold standard of diagnosis and is superior to ERCP in depicting biliary anatomy, including the intrahepatic bile duct.

Drip-infusion cholangiography CT involves the injection of intravenous biliary contrast agent and can well-delineate biliary anatomy and is less invasive than ERCP.

Treatment and prognosis

Once an anomalous pancreaticobiliary junction has been diagnosed, risk-reducing prophylactic surgical correction is recommended to reduce the risk of developing biliary cancer. Follow up of these cases is essential even years after prophylactic surgery as the residual bile ducts still have risk for cancer .

For patients without biliary dilatation, prophylactic cholecystectomy is recommended as the gallbladder is the commonest site for cancer development in these patients.

Complications

• pancreatitis
  • acute pancreatitis: is more common in children (30% of cases) irrespective of the presence of biliary dilatation .Symptoms can be mild and imaging findings can be subtle
  • chronic pancreatitis: much less common (3%) 
• biliary stones: within the bile ducts or gallbladder
• cholangitis
• biliary tract carcinoma: e.g. cholangiocarcinoma, gallbladder carcinoma 

History and etymology

Anomalous pancreaticobiliary junction was first described by Arnolds in 1906 in an autopsy case in Germany .

Siehe auch:

• Duodenaldivertikel
• Choledochuszyste
• Akute Pankreatitis
• Pankreasgang
• abgehängter Pankreasgang
• biliary tract carcinoma