Autoimmune pancreatitis (AIP) type 1 is characterized by diffuse or local enlargement of the pancreas demonstrated by imaging modalities, increased serum IgG4, and pathologic findings of abundant infiltration by IgG4-positive plasma cells, obliterative phlebitis, and storiform fibrosis [1, 2]. Pathologically, AIP type 2 shows lesions with neutrophilic infiltrates representing idiopathic duct-centric chronic pancreatitis . In Japan, AIP type 1 is common, while AIP type 2 is rare, differing from frequencies in the USA and Europe. Abdominal ultrasonography (US) is the initial imaging examination performed following blood tests in patients with jaundice, exacerbation of diabetes mellitus, or abdominal pain – all common symptoms of AIP. Sometimes, AIP is detected in asymptomatic patients by mass screening programs . In this section, we describe US findings in AIP type 1.
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