IgG4-related cholangitis (IgG4-SC) is the biliary manifestation of IgG4-related disease spectrum. It frequently coexists with autoimmune pancreatitis (AIP) in 60-80% of cases. It is characterized by diffuse or segmental bile duct wall thickening and poses the most important differential diagnostic challenge with cholangiocarcinoma. Plasma IgG4 levels are elevated (>135 mg/dL) and dramatic response to steroid therapy is pathognomonic. Four types of bile duct involvement are defined: Type 1 (distal CBD only), Type 2 (distal CBD + intrahepatic), Type 3 (hilar + distal CBD + intrahepatic), Type 4 (hilar only). HISORt criteria are used for diagnosis. If untreated, it may progress to secondary biliary cirrhosis.
Age Range
40-80
Peak Age
60
Gender
Male predominant
Prevalence
Rare
IgG4-related cholangitis is a chronic fibro-inflammatory condition characterized by dense infiltration of IgG4-positive plasma cells in the bile duct wall. Pathologically, it shows three cardinal features: (1) dense lymphoplasmacytic infiltration (IgG4+/IgG+ ratio >40%), (2) storiform (wicker-basket pattern) fibrosis, and (3) obliterative phlebitis. This inflammatory process causes concentric thickening of the bile duct wall — reflected in imaging as uniform or segmental wall thickening with homogeneous contrast enhancement. Periportal and periductal fibrosis narrows the duct lumen creating upstream biliary dilatation. However, unlike PSC, the duct wall is smooth and symmetric — irregular contour and beaded appearance are not expected in IgG4-SC. With steroid therapy, the inflammatory infiltrate regresses and duct thickening dramatically decreases — this therapeutic response has both diagnostic and prognostic significance.
Marked regression of bile duct wall thickening, periductal edema, and biliary dilatation after 2-4 weeks of steroid therapy — pathognomonic therapeutic response for IgG4-related cholangitis. Pre- and post-treatment MR comparison is the strongest evidence in diagnostic uncertainty. Cholangiocarcinoma does not respond to steroid therapy.
Smooth, concentric, symmetric bile duct wall thickening with prominent homogeneous enhancement on portal venous phase. Thickening may be diffuse (along the entire extrahepatic duct) or segmental. Wall thickness is typically 2-5 mm. Unlike the irregular, asymmetric thickening of cholangiocarcinoma, IgG4-SC maintains smooth inner and outer contours. Upstream biliary dilatation is seen proximally. When AIP coexists, diffuse pancreatic enlargement ('sausage pancreas') and peripancreatic capsule-like rim are notable.
Report Sentence
Smooth concentric wall thickening and homogeneous enhancement of the extrahepatic bile duct are noted, consistent with IgG4-related cholangitis.
Hyperintense periductal halo around bile ducts on T2-weighted images — reflecting inflammatory edema and lymphoplasmacytic infiltration. Thickened duct wall shows intermediate-to-high T2 signal. Symmetric involvement may be seen in both intrahepatic and extrahepatic ducts. MRCP demonstrates ductal narrowing and upstream dilatation — unlike PSC, duct wall thickening continues between strictures in IgG4-SC, whereas in PSC thin-walled segments intervene ('beaded' appearance).
Report Sentence
Hyperintense periductal halo and wall thickening around bile ducts on T2-weighted series are noted; IgG4-related cholangitis should be primarily considered.
MRCP shows segmental strictures of bile ducts but the 'beaded' appearance characteristic of PSC is absent. In IgG4-SC, duct segments between strictures are also narrowed due to thickened wall — in PSC, segments between strictures appear normal or dilated. Distal CBD is the most commonly affected region (70%), hilar involvement is less frequent. In the presence of AIP, pancreatic duct narrowing (>1/3 length) may also be seen. Long-segment (>12 mm) smooth stricture favors IgG4-SC, while short-segment irregular stricture favors cholangiocarcinoma.
Report Sentence
Segmental bile duct strictures are seen on MRCP without the beaded appearance characteristic of PSC; consistent with IgG4-related cholangitis.
Persistent or increasing contrast enhancement of thickened bile duct wall on delayed phase (3-5 minutes) — reflecting slow contrast accumulation in fibrotic tissue. Wall enhancement is mild in early arterial phase, progressively increasing in portal venous and delayed phases. This delayed enhancement pattern is similar to the desmoplastic reaction of cholangiocarcinoma, but wall thickening in IgG4-SC is more homogeneous and symmetric. Periductal soft tissue thickening and haziness of surrounding fat planes may be seen.
Report Sentence
Progressive increasing contrast enhancement of thickened bile duct wall on delayed phase is noted, consistent with fibrotic/inflammatory process.
Bile duct wall thickening (>1.5 mm) with proximal biliary dilatation on US. Thickened wall appears hypoechoic — with smooth and concentric characteristics. Gallbladder wall may also be thickened as part of IgG4-related disease. If diffuse hypoechogenicity and enlargement of pancreatic head due to AIP is seen, it strongly supports the diagnosis. CBD diameter exceeds 6 mm with accompanying intrahepatic duct dilatation.
Report Sentence
Hypoechoic wall thickening of extrahepatic bile duct with proximal biliary dilatation is noted.
Diffusion restriction of thickened bile duct wall on DWI — bright signal at high b-value, low value on ADC map. Associated with active inflammation period and useful for evaluating treatment response. Diffusion restriction decreases or disappears after steroid therapy. Diffusion restriction is also seen in cholangiocarcinoma but thickening in IgG4-SC is longer segment and more homogeneous.
Report Sentence
Diffusion restriction of thickened bile duct wall is noted, consistent with active inflammatory process.
Linear FDG uptake along bile ducts on PET-CT — reflecting inflammatory activity. Uptake is more diffuse and linear compared to focal intense FDG uptake of cholangiocarcinoma. If AIP coexists, diffuse FDG uptake in pancreas is also seen. Decrease in FDG uptake after treatment is used for response assessment. SUVmax is generally lower than cholangiocarcinoma but differentiation may be difficult especially in the presence of focal uptake.
Report Sentence
Linear FDG uptake along bile ducts is noted on PET-CT, reflecting inflammatory activity consistent with IgG4-related cholangitis.
Criteria
Distal common bile duct involvement only — type most frequently associated with AIP
Distinct Features
Pancreatic segment CBD narrowing, AIP findings in pancreatic head frequently accompany
Criteria
Distal CBD + intrahepatic duct involvement — diffuse stricture pattern mimicking PSC
Distinct Features
Intrahepatic strictures may be difficult to distinguish from PSC; IgG4 level and steroid response critical
Criteria
Combined involvement of hilar, distal CBD, and intrahepatic ducts — most diffuse type
Distinct Features
Diffuse involvement may be confused with PSC overlap; biliary biopsy may be needed
Criteria
Isolated hilar bile duct involvement — type most commonly confused with Klatskin tumor (hilar cholangiocarcinoma)
Distinct Features
Preoperative biopsy and IgG4 immunostaining critical; unnecessary Whipple surgery must be avoided
Distinguishing Feature
Cholangiocarcinoma shows irregular asymmetric mass/thickening and does not respond to steroids; IgG4-SC shows smooth symmetric thickening and regresses with steroids
Distinguishing Feature
PSC shows beaded appearance + irregular multisegmental strictures; IgG4-SC shows long-segment smooth strictures with thickened duct wall between strictures
Distinguishing Feature
Distal cholangiocarcinoma tends to form focal mass and may show vascular invasion; IgG4-SC Type 1 shows diffuse distal thickening without vascular invasion
Distinguishing Feature
Acute cholangitis presents acutely with fever/leukocytosis and obstructive cause (stone, stent) is identified; IgG4-SC has chronic course with elevated serum IgG4
Distinguishing Feature
Benign biliary stricture typically shows localized narrowing post-surgery/trauma; IgG4-SC shows multifocal or diffuse involvement with elevated IgG4
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
3-monthIgG4-related cholangitis responds dramatically to steroid therapy (prednisolone 0.6 mg/kg/day, 2-4 weeks). However, initiating treatment without confirming diagnosis may mask cholangiocarcinoma — biliary biopsy and IgG4 immunostaining are important. Untreated cases may develop secondary biliary cirrhosis. Relapse rate is 30-50% and rituximab may be used as second-line therapy. Serum IgG4 level is used for monitoring treatment response.
IgG4-related cholangitis is critically important as a cholangiocarcinoma mimicker. Serum IgG4 levels and other organ involvement (autoimmune pancreatitis, retroperitoneal fibrosis) aid diagnosis. Dramatic response to steroid therapy is diagnostic and prevents unnecessary surgery.