Imaging diagnosis of autoimmune pancreatitis: computed tomography and magnetic resonance imaging

Abstract

Autoimmune pancreatitis (AIP) is a pancreatic phenotype of IgG4-related systemic disease. Since its first description in the literature, characteristic imaging features have gradually become known to many clinicians encompassing various specialties in the past quarter century. CT and MRI have been the workhorses for imaging diagnosis of AIP. Typical features include sausage-like swelling of the focal or entire pancreas, duct-penetrating sign, a capsule-like rim of the affected lesions, and homogeneous delayed enhancement or enhanced duct sign after contrast administration, as well as characteristic combined findings reflecting coexisting pathologies in the other organs as a systemic disease. In this review, recent and future developments in CT and MRI that may help diagnose AIP are discussed, including restricted diffusion and perfusion and increased elasticity measured using MR.

Keywords: Autoimmune pancreatitis; Computed tomography; Diffusion-weighted image; IgG4; MR elastography.

Fig. 1

A male patient in his 70 s with typical autoimmune pancreatitis (AIP). a There is localized sausage-like swelling of the pancreas affected by AIP (large arrows). These lesions are hypodense during the pancreatic phase as compared to the normal pancreas (small arrow). Typical rim enhancement (arrowheads) demarcating the pancreatic tail is seen. b The same coronal section on delayed-phase CT reveals the lesion is hyperdense during the delayed phase compared to the normal pancreatic parenchyma (small arrow). The rim is also discernible in the delayed phase (arrowheads)

Fig. 2

A male patient in his 70 s with autoimmune pancreatitis (AIP). a Seven years before the onset of AIP, there was no pancreatic swelling on contrast-enhanced CT (CECT). b At the onset of AIP, there is distinct sausage-like swelling of the pancreatic body to tail on CECT. The area affected by AIP is a homogeneously less enhanced area (large arrow) as compared to the unaffected area (small arrow). c One year after initiation of prednisolone, the affected lesion returned to a normal size and enhancement on CECT (arrow)

Fig. 3

A female in her 60 s with typical autoimmune pancreatitis. a Axial contrast-enhanced CT in pancreatic phase. The pancreas is swollen as a whole, and punctate contrast-enhanced areas inside (arrowheads), as well as a typical band-shaped structure demarcating the lesion (arrows), are shown. b Coronal reconstruction of the same phase. Punctate contrast-enhanced areas (arrowheads) and a band-shaped structure surrounding the lesion (arrows) are also shown on the coronal image

Fig. 4

Coronal reconstruction images of contrast-enhanced portal-venous phase CT of a male in his 70 s with typical autoimmune pancreatitis. a Contrast-enhanced segments demarcating the wall of the main pancreatic duct (enhanced duct sign) are observed (arrowhead). b The enhancement demarcating the common bile duct wall is also evident (arrows), reflecting coexisting sclerosing cholangitis

Fig. 5

A male patient in his 70 s. On T2-weighted image, autoimmune pancreatitis-affected area shows slightly high intensity demarcated by a low-intensity rim

Fig. 6

Typical MRI images seen in a male patient in his 50 s with autoimmune pancreatitis. a The lesion is hypointense on fat-saturated T1-weighted image (arrows). b Multiple stenotic segments of the main pancreatic duct (skip narrowing and the icicle sign) are seen (arrowheads) on MRCP

Fig. 7

A male patient in his 70. a On diffusion-weighted image, a homogeneously hyperintense body to tail (arrow) suggests highly cellular plasmacyte proliferation seen in autoimmune pancreatitis. b On the ADC map, the ADC value of the lesion is 0.8 × 10^–3 mm²/s

Fig. 8

A male in his 50 s with IgG4-related autoimmune pancreatitis (AIP) associated with pathologically proven desmoplastic inflammatory pseudotumor. a Contrast-enhanced T1-weighted image showing delayed positive enhancement of the lesion in the pancreatic head (arrow). b A color-coded stiffness map shows a high stiffness of 6.2 kPa in the lesion (arrow), higher than previously reported values for AIP