Imaging: EUS and IDUS
EUS is an important procedure for the differential diagnosis of type 1 autoimmune pancreatitis (AIP) from other pancreatic diseases because IgG4-SC is often associated with type 1 AIP. Bile duct wall thickening is considered the EUS finding of IgG4-SC with type 1 AIP. Cholangiocarcinoma (CCA) and primary sclerosing cholangitis (PSC) are important diagnoses that should be differentiated from IgG4-SC. IDUS findings of non-stricture bile duct lesions are different between IgG4-SC and CCA. The thickening of the bile duct wall in non-stricture lesion is the most characteristic IDUS finding of IgG4-SC. The IDUS findings of stricture lesions are also different between IgG4-SC and PSC. IDUS is a useful modality for differentiating IgG4-SC from CCA and PSC, as the details of bile duct wall thickening are easily observable.