Type 1 autoimmune pancreatitis with histologically proven granulocytic epithelial lesions

There are two distinct subtypes of autoimmune pancreatitis (AIP): type 1 and type 2. Type 1 AIP is the pancreatic manifestation of systemic fibroinflammatory disease, which is named as IgG4-related disease. On the other hand, type 2 AIP is a pancreatic disorder that is not associated with IgG4. Type 1 and type 2 AIP have different clinical profiles and histologic findings. We present a 22-year-old man who has been diagnosed as type 1 AIP with histologically proven granulocytic epithelial lesion after surgical resection for pancreatic head mass. Since the patient had no pancreatic duct narrowing, elevation of serum IgG4, and other organ involvement, it was very difficult to diagnose preoperatively. This is a rare and interesting case in which histologic features of type 1 and type 2 AIP coexist.