Autoimmune Pancreatitis
This chapter outlines aspects of pancreatic imaging for type 1 autoimmune pancreatitis (AIP). AIP is subclassified as either type 1 (IgG4-related) or type 2 (granulocytic epithelial lesions) according to the International Consensus of Diagnostic Criteria
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10
Kazuichi Okazaki
10.1
Introductory Remarks
The disease concept of autoimmune pancreatitis (AIP) was proposed in 1995 by Yoshida et al. [1], and subsequently a subset of patients with this condition have been recognized to have the pancreatic manifestation of IgG4-related disease (IgG4-RD) [2]. The concept of AIP has undergone changes through the years and is now recognized internationally as being classified into two distinct types that in fact represent different diseases altogether [3, 4]. The history of the understanding of AIP over the past two decades is described in the chapter by Notohara (Chap. 21). AIP is subclassified according to the International Consensus of Diagnostic Criteria (ICDC) for Autoimmune Pancreatitis as either type 1 (IgG4-related) or type 2 (granulocytic epithelial lesions). Both types of AIP present with pancreatic swelling, mass formation, or complicating bile duct lesions, often leading to obstructive jaundice. These features can be difficult or impossible to separate from adenocarcinoma of the pancreas or cholangiocarcinoma on the basis of the clinical and radiologic findings alone. Type 1 (IgG4-related) AIP accounts for the great majority of cases in Japan. This condition, once termed lymphoplasmacytic sclerosing pancreatitis, is characterized histopathologically by lymphocytic and IgG4-positive plasmacytic cell infiltration, obliterative phlebitis, and fibrosis [3, 5, 6]. Type 2 AIP, once termed idiopathic duct-centric chronic pancreatitis (IDCP) [7], appears to be more common in Western countries than in Japan, but type 1 AIP still accounts for the majority of cases outside of Japan, as well. Type 2 AIP is characterized by granulocytic epithelial lesions (GEL) [5, 8], but its etiopathogenesis and pathophysiology are obscure. Revised diagnostic criteria focusing on type 1 AIP have K. Okazaki (*) Division of Gastroenterology and Hepatology, The third Department of Internal Medicine, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi City, Osaka 570-8506, Japan e-mail: [email protected]
recently been prepared by the Japan Pancreas Society and a research group of the Japanese Ministry of Health [5]. In this chapter, I outline pancreatic imaging against the background of these new diagnostic criteria.
10.2
Autoimmune Pancreatitis Diagnostic Criteria 2011 in Japan [9]
The 2011 Japanese diagnostic criteria are listed in the Table 10.1. A variety of changes from previous criteria were adopted: (1) classification of the extent of ICDC lesion involvement (diffuse, localized) on pancreatic parenchyma imaging; (2) simplification of the classification of ICDC diagnostic items into levels 1 and 2; (3) blood test findings limited to IgG4; (4) pathological findings limited to type 1 (IgG4-related) AIP; and (5) other organ involvement. In addition, the response to glucocorticoids was adopted as an optional criterion. With regard to the diagnosis, to avoid discrepancies with ICDC, various combinations of the diagnostic items are adopted to provide definite, probable, and pos
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