Autoimmune pancreatitis: an overview from pathologists’ perspective with emphasis on recent advances

Autoimmune pancreatitis (AIP) is an inflammatory condition of the pancreas of unknown etiology. It is not a homogenous entity; two types have been recognized and they are currently named type 1 and type 2 AIP. Both types have overlapping radiological features and their clinical presentation can be similar, but their histologic appearance is different and the underlying pathophysiological processes appear to be different as well. Type 1 AIP, previously known as lymphoplasmacytic sclerosing pancreatitis, is part of the IgG4-related disease spectrum, a multisystemic fibroinflammatory condition that affects multiple organs in a synchronous or metachronous way. Type 2 AIP, previously known as duct-centric chronic pancreatitis or granulocyte epithelial lesion (GEL)-positive pancreatitis, is not part of the IgG4-related disease spectrum, and is not associated with other organ involvement. This review focuses on the most recent advances in their pathogenesis, diagnosis, and treatment with particular attentions to histologic diagnostic criteria. It also discusses the differential diagnoses.