Autoimmune pancreatitis: imaging findings on contrast-enhanced MR, MRCP and dynamic secretin-enhanced MRCP

This study retrospectively determined magnetic resonance (MR), MR cholangiopancreatography (MRCP) and secretin-MRCP findings in patients with autoimmune pancreatitis (AIP). The MR examinations of 28 patients with histopathologically proven AIP were reviewed. In 14 cases, secretin-enhanced MRCP was performed. The observers evaluated pancreatic parenchymal enlargement, signal intensity abnormalities, enhancement, vascular involvement, bile-duct diameter and main pancreatic duct (MPD) narrowing (diffuse/focal/segmental). After secretin administration, the presence of the "duct-penetrating" sign was evaluated. MR imaging showed diffuse pancreatic enlargement in 8/28(29%) cases, focal pancreatic enlargement in 16/28 (57%) cases and no enlargement in 4/28 (14%) cases. The alteration of pancreatic signal intensity was diffuse in 8/28 (29%) cases (eight diffuse AIP) and focal in 20/28 (71%) cases (20 focal AIP). Delayed pancreatic enhancement was present in all AIP, with peripheral rim of enhancement in 8/28 (29%) AIP (1/8 diffuse, 7/20 focal); vascular encasement was present in 7/28 (25%) AIP (1/8 diffuse, 6/20 focal); distal common bile duct narrowing was present in 12/28(43%) AIP (5/8 diffuse, 7/20 focal). MRCP showed MPD narrowing in 17/28 (61%) AIP (4/8 diffuse, 15/20 focal), MPD dilation in 8/28(29%) AIP (3/8 diffuse, 5/20 focal) and normal MPD in1/8 diffuse AIP. Secretin-MRCP showed the duct-penetrating sign in 6/14(43%) AIP (one diffuse AIP with MPD segmental narrowing, five focal AIP with MPD focal narrowing), demonstrating integrity of the MPD. Delayed enhancement and MPD stenosis are suggestive for AIP on MR and MRCP imaging. Secretin-enhanced MRCP is a problem-solving tool in the differential diagnosis between focal AIP and ductal adenocarcinoma.