Autoimmune (IgG4) Pancreatitis

 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

Nov 16, 2016 | Posted by in GASTROINTESTINAL IMAGING | Comments Off on Autoimmune (IgG4) Pancreatitis

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