Endoscopic retrograde cholangiopancreatography and intraductal ultrasonography in the diagnosis of autoimmune pancreatitis and IgG4-related sclerosing cholangitis

Endoscopic retrograde cholangiopancreatography is used to evaluate the narrowing of the main pancreatic duct in autoimmune pancreatitis (AIP) and biliary stricture in IgG4-related sclerosing cholangitis (IgG4-SC). Intraductal ultrasonography enables detailed visualization of the thickening of the bile duct wall in IgG4-SC. Pancreatic cancer, cholangiocarcinoma, and primary sclerosing cholangitis are important mimicking conditions of AIP and IgG4-SC. Diffuse or segmental stricture without marked upstream dilatation is a typical pancreatographic finding in AIP. By contrast, a single, short stricture with marked upstream dilatation is a typical finding in pancreatic cancer. The cholangiogram of IgG4-SC is classified into four types based on biliary stricture location, and this cholangiogram classification is useful for the differential diagnosis of IgG4-SC. Endoscopic retrograde cholangiography can be used to distinguish between IgG4-SC and primary sclerosing cholangitis. A segmental/long and intrapancreatic stricture is a characteristic finding of IgG4-SC, whereas band-like strictures, a beaded or pruned-tree appearance, and diverticulum-like outpouching are characteristic of primary sclerosing cholangitis. The characteristic intraductal ultrasonographic findings of circular-symmetrical wall thickening, smooth outer and inner margins, and homogeneous internal echo at the biliary stricture site are useful for diagnosis of IgG4-SC. Thickening of the bile duct wall at non-stricture sites is also a typical intraductal ultrasonographic finding of IgG4-SC and can be used for differential diagnosis from cholangiocarcinoma. Transpapillary bile duct and duodenal papilla biopsy during endoscopic retrograde cholangiopancreatography are also useful in the diagnosis of IgG4-SC.