Diagnostic Imaging of Pancreatic and Biliary Involvement in IgG4-Related Disease: Key Imaging Features, Diagnostic Criteria and Differential Diagnosis

IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder characterised by elevated serum levels of IgG4 and multiorgan damage. Its diagnosis is challenging and requires a careful integration of clinical, radiological, serological and histological data. Pancreatic and biliary involvement is one of the most common manifestations of IgG4-RD, presenting as type 1 autoimmune pancreatitis (AIP) and IgG4-related sclerosing cholangitis (IgG4-SC), two entities that often occur synchronously and may mimic malignancy in the form of pancreatic ductal adenocarcinoma (PDAC) and cholangiocarcinoma, respectively. The main objective of this article is to illustrate the key imaging features of AIP and IgG4-SC on computed tomography (CT) and magnetic resonance imaging (MRI), providing a comprehensive review of their current diagnostic criteria and discussing their differential diagnosis with other benign and malignant conditions.