Autoimmune Pancreatitis (AIP) vs. Adenocarcinoma

​Autoimmune Pancreatitis (IgG4-related disease) is the great mimicker of pancreatic carcinoma, but unnecessary resection can be avoided by spotting its classic findings:

• ​Morphology: Diffusely enlarged, "sausage-shaped" pancreas with loss of the normal feathery clefts and lobulations.

• ​The "Halo" Sign: A thin, hypointense (on MRI) or hypoattenuating (on CT) capsule-like rim surrounding the affected gland.

• ​The Negatives: Crucially, AIP typically lacks significant main pancreatic duct dilatation (the duct through the lesion is often diffusely narrowed and irregular rather than completely obstructed) and lacks calcifications or peripancreatic fluid, differentiating it from both adenocarcinoma and standard chronic pancreatitis.