Fig. 4

Type 1 autoimmune pancreatitis (AIP) without concurrent pancreatic tumor. Axial pre-enhanced (a), arterial (b), venous (c) phase on CT and axial T2WI (d), T1WI (e), pancreatic (f), portal venous (g) and delayed venous (h) phase on MR imaging showed a focal lesion in the pancreatic head (straight black arrows). It presented with mass-like low-density on enhanced CT images (b and c). MR images showed a focal lesion with nearly homogeneous enhancement on enhanced sequences (f, g and h). The presence of focal mass-like lesion, combined with the characteristics of distal pancreatic parenchymal atrophy and main pancreatic ductal dilatation (curved white arrow on i), led to the high suspicion of pancreatic tumor. This patient finally underwent pancreatic resection and was proved to be pure AIP histologically. Kidney involvement was also observed on both CT and MR imaging (straight white arrows on b, c, d, f, g and h)