1.6　Histology

Fig.11.1　Imaging findings of pancreatic parenchyma and duct in type 1 AIP.（a）Computed tomography image showing diffuse swelling of the pancreas accompanied by a low-density capsule-like rim.（b）Diffusely irregular narrowing of the main pancreatic duct on endoscopic retrograde pancreatography

LPSP is a characteristic histological feature of type 1 AIP（Kamisawa et al.2013；Hart et al.2015a；Okazaki and Uchida 2015）.Type 2 AIP is characterized by idiopathic duct-centric chronic pancreatitis（IDCP）or granulocytic epithelial lesions（GEL）：the infiltration and accumulation of neutrophils in the epithelium of pancreatic ducts accompanied by ductal destruction（Notohara et al.2003）.ICDC currently requires that the histological specimens be acquired by endoscopic ultrasound（EUS）-trucut biopsy or operation（Shimosegawa et al.2011）.EUSguided fine-needle aspiration（EUS-FNA）is not included in the ICDC as a method for the histological evaluation because it is difficult to obtain adequate specimens for histopathological analysis（Shimosegawa et al.2011）.However，several reports have suggested that EUS-FNA is useful to diagnose AIP.Kanno et al.（2015b）reported that AIP could be histologically diagnosed according to ICDC in 20/25（80%）patients using EUSFNA with a 22-G needle（Fig.11.2）.Kanno et al.（2016）further validated their findings by a prospective multicenter study.They showed that 45/78（57.7%）patients could be diagnosed with LPSP（levels 1 or 2）according to ICDC.(https://www.daowen.com)