Up to now we have found 8 cases of AIP in our institution. Four cases were diffuse type AIP (fig. 1) and one was a focal type (fig. 2). The other three cases were atypical diffuse type, with respected parenchyma in the pancreatic head and/or uncinate process. The latter finding has not been described in previous articles to our knowledge, and is a potential cause of error due to the preserved parenchyma has a solid and nodular appeareance with higher density and contrast enhancement than the rest of the pancreas. This finding, specially on CT, may lead to a wrong PC diagnosis. On MRI the spared focus shows normal parenchyma characteristics, mainly on T1WI before and after contrast injection, and the affected parenchyma shows typical AIP findings (fig. 4, 5 and 6).

In all our cases affected parenchyma was hypointense on T1WI and hyperintense on T2WI respect to liver parenchyma. In 3 cases there was a hypodense halo on CT, that corresponded to a hypointense pseudocapsule on T2WI (fig. 7). All cases showed diminished contrast enhancement on the pancreatic phase, with later enhancement in 5 cases.

In 3 cases there was biliary dilatation and the pancreatic main duct was compressed in 5 cases and mildly dilated in 3 cases without duct-penetrating sign.

As we mentioned before, vascular involvement is not a useful characteristic to distinguish AIP from PC. In 5 cases, there was any grade splenoportal confluence stenosis (fig. 8), and we found a partial portal thrombosis in one case.

There were four cases with extrapancreatic involvement. One case showed biliary infiltration with choledocal parietal thickening, bilateral renal solid lesions with mild contrast enhancement, lymphadenopathies around the celiac trunk, and diffuse enlargement of submandibular glands (fig. 9). In two cases there was choledocal parietal thickening, and in one there was a solitary kidney lesion (fig. 10).

One case, with a hystologic diagnosis of type 2 AIP, later developed a ulcerative colitis.

Definitive diagnosis in our patients was made after biopsy or surgery, or with a combination of radiological findings, serology and/or response after corticoid treatment.

In two cases diagnosis was only made after surgical resection: one case of focal type AIP that couldn’t be presurgically distinguished from PC, and other one with severe biliary dilatation and abrupt diameter change and splenoportal stenosis that led to the misdiagnosis of PC.

A biopsy was performed in three cases. In two AIP was diagnosed, and the other one showed chronic pancreatitis with inflammatory non-specific infiltrate. In all three cases radiologic findings were clearly suggestive of AIP, and response after corticoid treatment confirmed the diagnosis. 

After corticoid treatment in our 6 cases without surgery, there was partial or complete response. In most of them the pancreas became smaller and atrophic with intensity decrease in T2w images, with the parenchyma remaining totally or partially hypointense on T1w images (fig. 11).