Hepatic inflammatory pseudotumor (inflammatory myofibroblastic tumor — IMT) is a rare benign lesion composed of myofibroblasts and chronic inflammatory cell infiltration. It closely mimics malignancy (especially cholangiocarcinoma and metastasis) on imaging, and diagnosis is usually made by biopsy. Two main etiological subgroups exist: (1) idiopathic/infectious type — after biliary infection or portoenterostomy, (2) IgG4-related type — may be associated with autoimmune pancreatitis. ALK (anaplastic lymphoma kinase) gene rearrangement is detected in some cases. Complete resection is curative, steroid therapy is effective in IgG4-related type.
Age Range
30-70
Peak Age
50
Gender
Male predominant
Prevalence
Rare
Inflammatory pseudotumor consists of clonal or reactive proliferation of myofibroblasts with dense infiltration of plasma cells, lymphocytes, and histiocytes. Two fundamental mechanisms are proposed in pathogenesis: (1) Infectious/reactive pathway — bacterial infection from portal venous system (especially E. coli, Klebsiella) triggers hepatic inflammatory response, myofibroblast activation and fibrosis develop. (2) Neoplastic/immunological pathway — ALK gene rearrangement drives myofibroblast proliferation (true neoplasm); IgG4-positive plasma cell infiltration reflects hepatic involvement of systemic IgG4-related disease. Delayed enhancement reflects the dense fibrous tissue component in the tumor — contrast accumulates late and washes out late in fibrous stroma.
A hepatic mass showing peripheral enhancement in arterial phase progressing to homogeneous fill-in on delayed phase, without capsular retraction, is the signature finding of inflammatory pseudotumor. This pattern is similar to cholangiocarcinoma, but cholangiocarcinoma shows capsular retraction, biliary dilatation, and usually incomplete delayed fill-in.
Solitary hypodense mass, usually well-defined. Size may range from 1-25 cm (average 5-7 cm). Calcification is rare but may be seen in chronic cases. Biliary dilatation may accompany (if centrally located).
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A solitary hypodense mass measuring approximately ___ cm is seen in the liver.
Peripheral rim enhancement in arterial phase — the more vascularized inflammatory tissue at the lesion periphery enhances, central fibrous core does not yet enhance.
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Peripheral rim enhancement is seen at the lesion margin in arterial phase with the central area not enhancing.
Progressive homogeneous enhancement on delayed phase (3-5 min) — late contrast accumulation in fibrous tissue. This delayed fill-in is the most characteristic CT finding of inflammatory pseudotumor.
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Progressive homogeneous enhancement on delayed phase suggests a fibrous component-dominant lesion (inflammatory pseudotumor or cholangiocarcinoma).
Heterogeneous signal on T2: fibrous dominant areas hypointense, active inflammation and edema areas hyperintense. The fibrous/inflammatory ratio determines T2 appearance. Peripheral hyperintense halo (active inflammation zone) may be seen.
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The lesion shows heterogeneous signal on T2 with coexisting hypointense (fibrous) and hyperintense (inflammatory) components.
Variable diffusion restriction — depending on inflammatory cell density. Diffusion restriction may be observed in areas of dense inflammation (low ADC). Diffusion restriction is less prominent in fibrous dominant areas.
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Variable diffusion restriction is observed in the lesion on diffusion-weighted imaging.
Hypoechoic mass, well-defined or ill-defined margins. Perilesional hyperechoic halo (inflammatory reaction) may be seen. US findings are non-specific and cannot exclude malignancy.
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A hypoechoic mass is seen in the liver, and contrast-enhanced CT or MRI is recommended for further characterization.
Criteria
Reactive inflammatory proliferation developing after biliary infection, portoenterostomy, or pylephlebitis. Polyclonal plasma cell infiltration.
Distinct Features
Fever and inflammatory markers (CRP, leukocytosis) may accompany. May shrink with antibiotic therapy. Located adjacent to portal vein branches (portal infection pathway). ALK negative. Spontaneous regression may occur.
Criteria
Elevated serum IgG4 + tissue IgG4-positive plasma cell infiltration (>10/HPF). Hepatic involvement of systemic IgG4-related disease.
Distinct Features
May be associated with autoimmune pancreatitis, sclerosing cholangitis, retroperitoneal fibrosis. Dramatic response to steroid therapy (significant size reduction). Serum IgG4 is diagnostic guide.
Criteria
ALK gene rearrangement positive — true neoplasm (clonal myofibroblast proliferation). More common in children and young adults.
Distinct Features
May be locally aggressive and malignant transformation (inflammatory fibrosarcoma) has been reported in rare cases. ALK inhibitors (crizotinib) may be effective in treatment. Recurrence risk is higher — complete resection is recommended.
Distinguishing Feature
Capsular retraction is typical in cholangiocarcinoma (fibrous core of tumor pulls surrounding parenchyma). Capsular retraction is absent in inflammatory pseudotumor. Peripheral biliary dilatation and vascular invasion are more common in cholangiocarcinoma. CA 19-9 may be elevated in cholangiocarcinoma, remains normal in inflammatory pseudotumor. On delayed phase, usually incomplete fill-in in cholangiocarcinoma, complete homogeneous fill-in in inflammatory pseudotumor.
Distinguishing Feature
Abscess shows central fluid collection (CT density 0-20 HU), double target sign (inner wall enhancement + peripheral edema halo). Inflammatory pseudotumor is a solid mass without central fluid. Abscess is clinically accompanied by septic picture (high fever, leukocytosis, positive blood culture).
Distinguishing Feature
Hepatic lymphoma usually shows homogeneous hypointense mass with minimal or no enhancement. Inflammatory pseudotumor shows prominent delayed phase enhancement. Lymphoma is accompanied by B symptoms (fever, night sweats, weight loss) and lymphadenopathy. LDH elevation is more typical in lymphoma.
Urgency
routineManagement
medicalBiopsy
NeededFollow-up
3-monthInflammatory pseudotumor is a benign lesion but malignancy (especially cholangiocarcinoma) cannot be excluded by imaging — biopsy is almost always necessary. In IgG4-related type, serum IgG4 level should be measured and if elevated, steroid therapy should be attempted (dramatic response expected — significant shrinkage in 2-4 weeks). In infectious type, regression may be seen with antibiotic therapy. In ALK-positive type, complete surgical resection is curative. 3-month CT/MRI follow-up is recommended to assess treatment response. If no steroid response or continued growth, malignancy has not been excluded — surgical resection or repeat biopsy required.
Definitive diagnosis of inflammatory pseudotumor usually requires biopsy because imaging cannot exclude malignancy. If IgG4-related disease is identified, steroid therapy can be applied. Spontaneous regression or decrease in size with treatment may be observed on follow-up imaging.