Autoimmune (IgG4) Pancreatitis

Published on 19/07/2015 by admin

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Last modified 19/07/2015

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 Sausage-like enlargement of pancreas (with smooth contour) and loss of normal pancreatic lobulations

image Hypoattenuating halo or capsule around pancreas
image Absence of retroperitoneal fluid, fluid collections/pseudocysts, or inflammation
image Less enhancement than expected in arterial phase; parenchyma/capsule may show delayed enhancement
image Diffuse or segmental narrowing of pancreatic duct
image MRCP: Multiple discontiguous MPD/bile duct strictures which resolve after secretin (duct penetrating sign)
• Focal form

image Focal mass or localized enlargement of pancreas (usually head/uncinate) with delayed enhancement
image Lack of biliary or pancreatic ductal dilatation

TOP DIFFERENTIAL DIAGNOSES

• Pancreatic ductal adenocarcinoma
• Chronic pancreatitis
• Acute edematous pancreatitis

PATHOLOGY

• Two distinct histologic subtypes

image Type I: Lymphoplasmacytic sclerosing pancreatitis 

– Positive IgG4 tissue staining; serum IgG4 elevated
– Extrapancreatic organ involvement common (∼ 60%); inflammatory bowel disease in only 2-6%
– Older patients (usually > age 60) with M > F
image Type II: Idiopathic duct-centric pancreatitis

– No IgG4 tissue staining; serum IgG4 not elevated
– No extrapancreatic organ involvement; inflammatory bowel disease in 30%
– Younger patients (mean age 43) with M=F
image
(Left) Axial CECT shows diffuse infiltration and enlargement of the pancreas with loss of normal fatty lobulation. There is a hypodense halo or capsule image around the pancreas, with relatively little spread into adjacent tissues, compatible with autoimmune pancreatitis. All symptoms and signs resolved with steroid therapy.

image
(Right) Transhepatic cholangiogram in a patient with autoimmune pancreatitis shows multifocal strictures image indistinguishable from those of primary sclerosing cholangitis.
image
(Left) Axial CECT demonstrates a diffusely enlarged pancreas with a low attenuation halo image around its margin.

image
(Right) Coronal CECT from the same patient shows similar findings with a low attenuation capsule image around the enlarged pancreatic margin. Note the presence of biliary dilatation image in this patient with a history of biliary strictures, often associated with autoimmune pancreatitis.

TERMINOLOGY

Abbreviations

• Autoimmune pancreatitis (AIP)

Synonyms

• Lymphoplasmacytic sclerosing pancreatitis; primary sclerosing pancreatitis; tumefactive pancreatitis; non-alcoholic destructive pancreatitis

Definitions

• Immune-mediated fibroinflammatory disease primarily involving pancreas responding to steroid therapy

IMAGING

General Features

• Best diagnostic clue

image Diffusely/focally enlarged pancreas with hypodense halo
image No vascular involvement, calcifications, or pseudocysts
image Lack of significant dilatation of main pancreatic duct
• Location

image May be diffuse, multifocal, or focal/mass-forming
• Morphology

image Sausage-shaped appearance of pancreas

Imaging Recommendations

• Best imaging tool

image MRCP and gadolinium-enhanced MR

CT Findings

• Diffuse form

image Diffuse sausage-like enlargement of pancreas (with smooth contour) and loss of pancreatic lobulations
image Hypoattenuating halo or capsule around pancreas
image Often less enhancement than expected in arterial phase; delayed enhancement of involved parenchyma/capsule
image No retroperitoneal fluid collections or inflammation
image Lymphadenopathy common (20%) with similar halo or capsule
• Focal form

image Focal mass or localized enlargement of pancreas (usually head/uncinate) with delayed enhancement
• Diffuse or segmental narrowing of pancreatic duct
• Extrapancreatic imaging findings

image IgG4 cholangitis in 90%: May be indistinguishable from primary sclerosing cholangitis

– Stricture of common bile duct (CBD) ± intrahepatic ducts with hyperenhancement of duct wall
image Renal involvement in 35% of patients with AIP

– Round or wedge-shaped low attenuation parenchymal lesions
– Diffuse renal enlargement
– Perirenal soft tissue rind (mimicking lymphoma)
– Urothelial thickening in renal pelvis
image Retroperitoneal fibrosis, IgG4-related lung disease, and enlarged salivary glands or salivary gland mass
image IgG4-related lung disease

– Solid nodules, ground glass opacities, interstitial opacities

MR Findings

• Diffuse enlargement of pancreas (T1WI hypointense and T2WI hyperintense)
• Capsule of peripheral hypoenhancement and low T2WI signal with delayed enhancement
• Delayed enhancement of involved parenchyma
• MR cholangiopancreatography (MRCP): Multiple discontiguous main pancreatic duct/bile duct strictures

image Strictures resolve after secretin (duct-penetrating sign)
• DWI: Mildly restricted diffusion of affected tissue

image Cannot use DWI to differentiate focal AIP from pancreatic cancer

Ultrasonographic Findings

• Transcutaneous ultrasound is of limited value; may have normal appearance
• Endoscopic ultrasound

image Enlarged hypoechoic gland with sausage-like appearance, narrowed MPD, and thickening of CBD wall
image Echogenic interlobular septa

Nuclear Medicine Findings

• PET/CT

image 

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