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Autoimmune Pancreatitis (AIP) Type 1 and Type 2: An International Consensus Study on Histopathologic Diagnostic Criteria

Zhang, Lizhi MD*; Chari, Suresh MD; Smyrk, Thomas C. MD*; Deshpande, Vikram MD; Klöppel, Günter MD§; Kojima, Motohiro MD; Liu, Xiuli MD, PhD; Longnecker, Daniel S. MD#; Mino-Kenudson, Mari MD; Notohara, Kenji MD**; Rodriguez-Justo, Manuel MD††; Srivastava, Amitabh MD‡‡; Zamboni, Giuseppe MD§§; Zen, Yoh MD∥∥

doi: 10.1097/MPA.0b013e318233bec5
Original Articles

Objectives: To develop and validate histologic diagnostic criteria for autoimmune pancreatitis (AIP) and its types.

Methods: Thirteen pathologists participated in this 2-phase study to develop diagnostic criteria for AIP types 1 and 2 (phase 1) and validate them (phase 2). A virtual library of 40 resected pancreata with AIP and other forms of chronic pancreatitis (CP) was constructed. Readers reviewed the slides online and filled out a questionnaire for histopathologic findings and diagnosis.

Results: Diagnostic criteria for AIP and its types were proposed according to the results from the top 5 reviewers in phase 1. The interobserver agreement was significantly improved in phase 2 by applying the proposed diagnostic criteria. Features distinguishing AIP from alcoholic and obstructive forms of CP were periductal lymphoplasmacytic infiltrate, inflamed cellular stroma with storiform fibrosis, obliterative phlebitis, and granulocytic epithelial lesions. Although there was overlap, 2 types of AIP were recognized. Type 1 had dense lymphoplasmacytic infiltrate with storiform fibrosis and obliterative phlebitis, whereas type 2 was distinguished from type 1 by the presence of granulocytic epithelial lesions.

Conclusions: Autoimmune pancreatitis can be distinguished from other forms of CP with substantial interobserver agreement. The 2 types of AIP can be distinguished by the proposed consensus histopathologic diagnostic criteria.

Supplemental Digital Content is available in the text.

From the *Department of Laboratory and Anatomic Pathology, and †Divisions of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN; ‡Department of Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, MA; §Department of Pathology, University of Kiel, Kiel, Germany; ∥Division of Clinical Pathology, National Cancer Center Hospital East, Kashiwa Chiba, Japan; ¶Department of Anatomic Pathology, Cleveland Clinic, Cleveland, OH; #Department of Pathology, Dartmouth Medical School and Dartmouth-Hitchock Medical Center, Lebanon, NH; **Department of Pathology, Kurashiki Central Hospital, Kurashiki, Japan; ††Department of Pathology, University College London, London, UK; ‡‡Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA; §§Department of Pathology, University of Verona, Verona, Italy; and ∥∥Institute of Liver Studies, King's College Hospital, London, UK.

Received for publication July 29, 2011; accepted August 19, 2011.

Reprints: Lizhi Zhang, MD, Department of Laboratory and Anatomic Pathology, Mayo Clinic, 200 First St SW, Rochester, MN 55905 (e-mail:;;

The authors declare no conflict of interest or funding to disclose.

Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (

© 2011 Lippincott Williams & Wilkins, Inc.