Autoimmune pancreatitis associated with IgG4-related cholangitis: A radiologic-serologic correlation

A 42-year-old male patient with no significant past medical history presented with acute epigastric pain radiating to the back, associated with elevated serum lipase levels. An initial contrast-enhanced CT scan, performed outside our institution, suggested acute interstitial edematous pancreatitis. Subsequent abdominal ultrasound revealed dilatation of the intrahepatic bile ducts. The patient was referred to our hospital for further evaluation with magnetic resonance imaging (MRI). MRI demonstrated diffuse glandular enlargement of the pancreas with loss of normal lobulation. The pancreatic parenchyma showed marked diffusion restriction, surrounded by a peripheral capsule-like rim ( Fig. 1 , Fig. 2 , Fig. 3 ). Magnetic resonance cholangiopancreatography revealed a tapered stenosis of the main pancreatic duct without abrupt interruption. Associated findings included circumferential wall thickening of the distal common bile duct and the common hepatic duct with delayed contrast enhancement, along with upstream dilatation of the intrahepatic bile ducts’ ( Fig. 4 ). Fig. 1 Axial T2-weighted sequences show diffuse glandular enlargement with loss of normal lobulation, surrounded by a peripheral capsule-like rim (with arrow). Fig 1 dummy alt text Fig. 2 Axial DWI showing pancreatic parenchymal diffusion restriction (with arrow). Fig 2 dummy alt text Fig. 3 Axial T1-weighted images before and after contrast administration at the 3 dynamic phases show decreased intrinsic T1 signal intensity of the pancreas, with delayed pancreatic enhancement. Fig 3 – dummy alt text Fig. 4 Biliary MR sequences reveal a tapered stenosis of the main pancreatic duct and strictures of the common hepatic duct and distal common bile duct, while coronal T2-weighted images show regular circumferential wall thickening of the common hepatic duct (with arrow). Fig 4 dummy alt text Axial T2-weighted sequences show diffuse glandular enlargement with loss of normal lobulation, surrounded by a peripheral capsule-like rim (with arrow). Axial DWI showing pancreatic parenchymal diffusion restriction (with arrow). Axial T1-weighted images before and after contrast administration at the 3 dynamic phases show decreased intrinsic T1 signal intensity of the pancreas, with delayed pancreatic enhancement. Biliary MR sequences reveal a tapered stenosis of the main pancreatic duct and strictures of the common hepatic duct and distal common bile duct, while coronal T2-weighted images show regular circumferential wall thickening of the common hepatic duct (with arrow). Based on the characteristic imaging features and the associated biliary involvement, a diagnosis of type 1 autoimmune pancreatitis related to IgG4 disease was suspected. Serum IgG4 levels were subsequently measured and found to be elevated at 12 g/L, confirming the diagnosis.

Written and informant consent for publication of the case was obtained from the patient.

Autoimmune pancreatitis remains a diagnostic challenge, particularly in its focal form, due to its close resemblance to pancreatic ductal adenocarcinoma. A thorough imaging analysis, including evaluation of enhancement patterns, ductal morphology, diffusion-weighted imaging, and associated extrapancreatic manifestations, is essential for accurate diagnosis. The association with IgG4-related cholangitis and positive IgG4 serology, as illustrated in our case, strongly supports the diagnosis of type 1 AIP and underscores the systemic nature of the disease. Recognizing these features is crucial to ensure appropriate patient management and to prevent unnecessary invasive procedures or surgical treatment.

AIP is a rare fibro-inflammatory disease of the pancreas and is now recognized as a distinct form of chronic pancreatitis and an important cause of pancreatic pseudotumors [ 1 ]. It represents a major diagnostic challenge because its clinical and radiological presentation may closely mimic pancreatic ductal adenocarcinoma, potentially leading to unnecessary surgical intervention if not correctly identified [ 2 ]. The International Consensus Diagnostic Criteria emphasize a multimodal approach that combines imaging findings, serology, histology, other organ involvement, and response to steroid therapy, with imaging playing a pivotal role in the diagnostic algorithm [ 1 ]. Typical imaging findings of AIP include diffuse pancreatic enlargement with loss of normal lobulation, often described as a “sausage-shaped” pancreas [ 1 ]. In our case, MRI demonstrated diffuse enlargement predominantly involving the pancreatic head and body, associated with mild peripancreatic inflammatory changes and without evidence of necrosis or significant peripancreatic fluid collections. This enlargement was associated with a peripheral capsule-like rim, hypodense on computed tomography (CT) and hypointense on MRI, which corresponds histologically to inflammatory fibrosis and is considered a characteristic imaging feature [ 1 ]. Dynamic contrast-enhanced imaging usually demonstrates delayed homogeneous enhancement of the pancreatic parenchyma, reflecting progressive contrast uptake within fibrotic tissue, in contrast to pancreatic ductal adenocarcinoma, which typically shows poor and heterogeneous enhancement [ 3 ]. On MRI, diffuse low signal intensity on T1-weighted images is commonly observed and reflects diffuse inflammatory involvement of the gland [ 1 ]. Diffusion-weighted imaging provides additional diagnostic value in AIP. Type 1 AIP typically demonstrates lower apparent diffusion coefficient (ADC) values than pancreatic ductal adenocarcinoma, reflecting dense inflammatory cell infiltration and fibrosis [ 4 ]. Quantitative ADC analysis has been shown to be useful in differentiating focal type 1 AIP from pancreatic cancer, particularly in localized forms that mimic a neoplastic mass [ 4 ]. Furthermore, intravoxel incoherent motion diffusion-weighted MRI allows functional assessment of tissue diffusion and perfusion, contributing to both differential diagnosis and treatment monitoring [ 5 ]. A significant increase in ADC values after steroid therapy has been reported, supporting the role of diffusion imaging as a noninvasive biomarker of treatment response in AIP [ 5 ]. Evaluation of the main pancreatic duct using magnetic-resonnance cholangiopancreatography (MRCP) is crucial in the assessment of AIP [ 1 ]. In our patient, MRCP demonstrated diffuse smooth tapering stenosis of the main pancreatic duct without abrupt ductal interruption or marked upstream dilatation. Although a duct-penetrating sign was suspected, it could not be confidently demonstrated. The duct-penetrating sign, defined as visualization of the main pancreatic duct coursing through the inflamed pancreatic parenchyma without abrupt interruption, is considered highly suggestive of AIP [ 2 ]. This finding helps differentiate AIP from pancreatic cancer, in which the duct is more commonly abruptly obstructed or amputated at the level of the lesion [ 2 ]. However, this sign should not be interpreted in isolation and must always be correlated with other imaging and clinical findings [ 3 ]. Type 1 AIP is part of the spectrum of IgG4-related disease, which explains its frequent association with extrapancreatic organ involvement [ 1 ]. Biliary involvement is among the most common associated manifestations and represents an important diagnostic clue [ 3 ]. In our case, MRI and MRCP demonstrated smooth stenotic involvement of the distal common bile duct and common hepatic duct, associated with circumferential wall thickening and upstream intrahepatic bile duct dilatation . Imaging typically shows circumferential, smooth, and symmetrical thickening of the bile duct walls with delayed enhancement and relative preservation of the lumen [ 1 ]. This appearance differs from malignant biliary strictures or primary sclerosing cholangitis, which more often demonstrate irregular and asymmetric wall thickening, thereby supporting the diagnosis of IgG4-related sclerosing cholangitis in the appropriate clinical context [ 3 ]. The focal form of AIP remains the most challenging presentation because it may appear as a localized pancreatic mass [ 2 ]. In this setting, differentiation from pancreatic ductal adenocarcinoma is particularly difficult [ 2 ]. Although imaging features such as the duct-penetrating sign, delayed enhancement pattern, and diffusion-weighted imaging findings may favor AIP, they cannot definitively exclude malignancy [ [3] , [4] , [5] ]. Given the high prevalence and poor prognosis of pancreatic cancer, this diagnosis must always be considered when evaluating a focal pancreatic lesion, and a cautious, systematic diagnostic approach is mandatory [ 2 ]. In our patient, the initial CT examination performed elsewhere suggested acute interstitial edematous pancreatitis. However, subsequent MRI and MRCP findings were more suggestive of autoimmune pancreatitis than of routine acute pancreatitis. The diagnosis was supported by diffuse sausage-like pancreatic enlargement, smooth long-segment narrowing of the main pancreatic duct, associated biliary strictures, a capsule-like rim, and the absence of pancreatic necrosis or extensive peripancreatic fluid collections. These imaging findings, together with elevated serum IgG4 levels, strongly supported the diagnosis of type 1 AIP associated with IgG4-related cholangitis. The diagnostic value of the imaging findings was further strengthened by the coexistence of autoimmune pancreatitis and IgG4-related cholangitis, confirmed by elevated serum IgG4 levels. This association represents a characteristic manifestation of type 1 AIP and highlights the importance of integrating serological data with imaging features to support the diagnosis. The presence of biliary involvement together with positive IgG4 serology further reinforces the systemic nature of the disease and constitutes a strong argument against pancreatic malignancy, emphasizing the relevance and originality of this case.

Autoimmune pancreatitis (AIP) is a rare fibro-inflammatory form of chronic pancreatitis, in which the focal presentation may closely mimic pancreatic cancer on both clinical and imaging grounds. Since its recognition as a distinct entity, AIP has gained increasing attention due to its strong association with IgG4-related disease, particularly in type 1 AIP, which frequently presents with extrapancreatic organ involvement. Imaging plays a pivotal role in the diagnostic pathway, allowing recognition of characteristic features and guiding appropriate management while avoiding unnecessary surgical interventions. In this context, we report a case of autoimmune pancreatitis associated with IgG4-related cholangitis, confirmed by positive IgG4 serology, highlighting the complementary value of imaging and biological findings in establishing a confident diagnosis.