Sequential progression mechanism of AIP to confirmed chronic pancreatitis. (A) Narrowing of both Wirsung’s and Santorini’s ducts (arrows) by pancreatic head swelling causes pancreatic juice stasis in the upstream pancreatic duct. (B) Pancreatic juice stasis results in increased intra-pancreatic duct pressure that is resistant to typical AIP-specific MPD narrowing in the pancreatic body region, leading to MPD non-narrowing in this region (arrowheads). (C) In concert with relapse, these events finally result in severe calcification. (From Ref.).