Focal Autoimmune Pancreatitis Morphologically Mimicking Pancreatic Cancer: A Case Report and Literature Review.

BACKGROUND Autoimmune pancreatitis (AIP) is identified as an outlier in the clinical practice of chronic pancreatitis caused by autoimmune system dysfunction. AIP is classified into 3 subtypes: AIP type 1 and AIP type 2, which are both sensitive to corticosteroids, and the recently introduced AIP type 3. CASE REPORT We present a case of a patient who presented with painless obstructive jaundice. Computed tomography (CT) revealed hyperdense gallbladder material, further dilatation of intrahepatic bile ducts, and distention of the bile duct (15 mm). Based on the available clinical data, which were strongly compatible with pancreatic cancer, Whipple surgery was selected as the treatment for this case. The consequent histopathological report revealed areas of pancreatic parenchyma with fibrous connective tissue development and dense inflammatory cell infiltration with lymphocytes and plasmacytes, which showcased IgG4 positivity. The clinical results suggested a diagnosis of AIP type 1, and the patient was referred to his treating physician for further treatment of AIP. Preoperative histological examination of the pancreas, along with evaluation of the radiological and serological features, could have aided in determining the diagnosis of AIP type 1 pancreatitis despite the unique abnormality of this particular case. CONCLUSIONS Given the aforementioned conditions, AIP, even as a rare clinical entity, emerges as a canonical ailment and should be considered a viable possibility in clinical practice since it can exclude the patient from an unnecessary surgery.