IgG4-related sclerosing cholangitis (ISC) is the manifestation of biliary involvement of IgG4-related disease. Most patients present with obstructive jaundice. ISC may involve both the extrahepatic and the intrahepatic portions of the bile duct with extrahepatic ISC being much more common than intrahepatic disease. Extrahepatic bile duct involvement is the most commonly involved extrapancreatic site in autoimmune pancreatitis. ISC can present either as bile duct wall thickening with dense lymphoplasmacytic infiltration and marked interstitial fibrosis resulting in bile duct stricture or as hepatic tumefactive lesions. Gallbladder involvement has also been described. Morphologically, ISC is essentially similar to other forms of IgG4-related diseases, which is characterized by dense lymphoplasmacytic infiltrates, storiform fibrosis, obliterative phlebitis, and elevated numbers of IgG4-positive plasma cells. The intrahepatic ISC is also characterized by the presence of portal-based inflammatory nodules which are composed of lymphocytes, plasma cells, and eosinophils, admixed with fibroblasts. The primary clinical and radiologic differential diagnosis of ISC is primary sclerosing cholangitis and cholangiocarcinoma.
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