Splenic inflammatory pseudotumor (IPT) is a rare benign lesion of the spleen composed of reactive inflammatory cell infiltration and fibrous tissue proliferation. It may fall within the same spectrum as inflammatory myofibroblastic tumor (IMT), though true neoplastic potential remains debated. Histopathologically, it is characterized by a heterogeneous inflammatory infiltrate containing plasma cells, lymphocytes, histiocytes, and spindle-shaped myofibroblasts. The lesion typically ranges from 2-10 cm in size and usually presents as a solitary, well-circumscribed mass. Clinical presentation is nonspecific — fever, abdominal pain, weight loss, and elevated erythrocyte sedimentation rate are common. Etiology is incompletely understood; Epstein-Barr virus (EBV), mycobacterium, and autoimmune mechanisms have been implicated. On imaging, the heterogeneous enhancement pattern and variable signal characteristics make differentiation from malignant lesions (lymphoma, angiosarcoma) challenging, and definitive diagnosis typically requires histopathological examination after splenectomy. ALK (anaplastic lymphoma kinase) positivity is an important marker favoring inflammatory myofibroblastic tumor.
Age Range
20-70
Peak Age
50
Gender
Equal
Prevalence
Rare
Splenic inflammatory pseudotumor is a process characterized by myofibroblastic proliferation and dense inflammatory cell infiltration in response to chronic inflammatory stimulation. Histologically, three main patterns are recognized: (1) myofibroblast-dominant spindle cell pattern (compact fibrous stroma), (2) plasma cell-dominant pattern (vascularized loose stroma), and (3) sclerosing-hyalinized pattern (dense collagen deposition). This histological heterogeneity forms the basis for the variable enhancement pattern on imaging: myofibroblast-rich areas show earlier enhancement due to greater vascularity, while fibrous and hyaline areas demonstrate delayed enhancement — creating a heterogeneous enhancement pattern. Dense plasma cell infiltration increases cellular density, producing variable signal on T2-weighted MRI: the cellular-inflammatory component shows moderate T2 hyperintensity, while the fibrous component creates T2 hypointensity. On DWI, increased cellular density causes diffusion restriction — a finding that carries potential overlap with malignant lesions (especially lymphoma). In EBV-associated cases, viral transformation of B lymphocytes and triggering of polyclonal lymphoproliferative response can result in more prominent lymphocytic infiltration and a more homogeneous imaging pattern. Over time, dystrophic calcification may develop within the fibrous component, detected on CT as punctate or coarse calcifications.
The mixed signal pattern on T2-weighted MRI created by the coexistence of inflammatory and fibrous components is the most characteristic imaging finding of IPT. The inflammatory component shows T2 hyperintensity due to high water content, while the fibrous component creates hypointensity with short T2 relaxation time — this dual pattern is not seen in most other splenic lesions.
On unenhanced CT, a well-defined, homogeneous or mildly heterogeneous hypodense mass is seen relative to splenic parenchyma. Density typically ranges between 30-45 HU — higher than purely cystic lesions but lower than solid splenic tissue. The lesion margins are usually smooth and sharp; mild lobulated contour may be present in some cases. More homogeneous density is observed in fibrous component-dominant lesions, while mild heterogeneity may be seen in mixed inflammatory-fibrous composition. Rarely, dystrophic calcifications and internal necrotic/cystic areas may also be detected. Reactive edema in the surrounding splenic parenchyma may be present.
Report Sentence
A well-defined, mildly heterogeneous hypodense solid mass is seen in the spleen on unenhanced CT.
The lesion demonstrates heterogeneous enhancement in the arterial phase. Peripheral or nodular enhancement foci typically correspond to vascularized inflammatory tissue areas. The lesion center usually shows less enhancement — reflecting central fibrous or hyaline tissue. The enhancement pattern may mimic lymphoma or metastatic lesions. The normal heterogeneous zebra pattern enhancement of the spleen in arterial phase can complicate lesion evaluation; therefore, portal venous and delayed phase assessment is critical. A peripheral enhancement rim may be observed at the lesion borders, reflecting a fibrous capsule or peripheral vascularized zone.
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The splenic mass demonstrates heterogeneous enhancement in the arterial phase with peripheral enhancement foci.
On delayed phase (3-5 minutes), the lesion shows progressive enhancement — contrast retention becomes particularly prominent in fibrous component-dominant areas. The lesion may become more homogeneous compared to early phases as the expanded extracellular space of fibrous tissue accumulates contrast agent. This delayed enhancement pattern is characteristic of fibrous tissue and helpful in differentiation from lymphoma (typically homogeneous, early and persistent enhancement). Persistent central hypodensity suggests necrosis or hyalinized tissue. Rim enhancement at the lesion periphery may become more prominent on delayed phase.
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The splenic lesion demonstrates progressive enhancement and contrast retention on delayed phase, consistent with fibrous component.
On T2-weighted MRI, the lesion shows mixed signal intensity — this is the most characteristic MR finding of IPT. The inflammatory component (plasma cells, lymphocytes, loose stroma) demonstrates moderate-high T2 signal, while the fibrous component (collagen, hyaline) shows markedly low T2 signal. This mixture creates a heterogeneous hypointense-hyperintense mixed pattern relative to splenic parenchyma. In fibrous-dominant lesions, T2 hypointensity is more prominent, and this 'dark lesion' pattern suggests fibromatous lesions or sclerosing processes. Mild T2 signal increase from reactive edema may be seen in the surrounding splenic parenchyma. Necrotic or cystic degeneration areas can be recognized as distinct areas of high T2 signal.
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The splenic lesion demonstrates mixed signal intensity on T2W MRI with coexisting hyperintense inflammatory and hypointense fibrous components.
The lesion shows marked diffusion restriction on DWI — hyperintense signal at high b-values (b=800-1000) with low signal on ADC maps. Diffusion restriction reflects the high cellularity of the lesion. ADC values typically range between 0.8-1.2 × 10⁻³ mm²/s — higher than lymphoma (typically 0.5-0.8 × 10⁻³ mm²/s) but lower than benign cystic lesions. Heterogeneous appearance on ADC maps is typical due to mixed histological composition: inflammatory-cellular areas show lower ADC, while fibrous areas show higher ADC. This ADC heterogeneity may help differentiate IPT from lymphoma which typically shows homogeneously low ADC.
Report Sentence
The splenic lesion shows diffusion restriction on DWI with heterogeneous low signal on ADC maps.
On B-mode ultrasonography, a hypoechoic or mixed echogenicity, well-circumscribed solid mass is seen relative to splenic parenchyma. Echogenicity varies depending on histological composition: inflammatory component-dominant lesions appear more hypoechoic, while fibrous component-dominant lesions appear more isoechoic or mildly hyperechoic. Internal echo distribution is generally heterogeneous. Lesion margins are usually smooth and well-defined; a halo sign may be seen in some cases. Posterior acoustic enhancement is not observed (solid lesion). Internal cystic/necrotic areas may be detected as anechoic foci in large lesions.
Report Sentence
A well-circumscribed, heterogeneous hypoechoic solid mass is seen in the spleen on B-mode US.
Color Doppler ultrasonography shows variable internal vascularity within the lesion. In inflammatory component-dominant lesions, internal vascularity may be increased — low-resistance arterial flow is detected. In fibrous-dominant lesions, vascularity is more decreased, and peripheral vascularity predominates. Spectral Doppler shows a resistive index (RI) generally between 0.5-0.7 — these low-moderate resistance values reflect inflammatory neovascularization. Increased flow in the peripheral halo region may be detected in some cases.
Report Sentence
The splenic lesion demonstrates variable internal vascularity on Doppler ultrasound with low-moderate resistance arterial flow.
Criteria
Histologically dominated by spindle myofibroblast proliferation, scattered inflammatory cells within compact fibrous stroma. ALK positivity more frequent in this type. More common in younger patients.
Distinct Features
More homogeneous appearance on imaging, marked T2 hypointensity (dominant fibrous component), more prominent delayed enhancement. More uniform hypodense appearance on CT.
Criteria
Histologically dense plasma cell infiltration, loose vascularized stroma. EBV association more frequent in this type. Seen in middle-aged and older patients.
Distinct Features
More prominent T2 hyperintensity on imaging, more prominent arterial phase enhancement, more homogeneous diffusion restriction on DWI. Lower ADC values.
Criteria
Dense collagen deposition and hyalinized stroma dominant, inflammatory cells sparse. Generally in older patients — 'burned-out' inflammation phase.
Distinct Features
Marked T2 hypointensity, minimal or delayed enhancement, calcification more frequent on CT. More echogenic on US. Minimal diffusion restriction on DWI.
Criteria
EBV-encoded RNA (EBER) positivity confirmed by in-situ hybridization. More frequent in immunosuppressed patients. Carries lymphoproliferative spectrum risk.
Distinct Features
More homogeneous pattern, may be bilateral/multiple, lymphadenopathy may accompany — strongly mimics lymphoma. FDG uptake may be increased on PET-CT.
Distinguishing Feature
Lymphoma typically shows homogeneous low T2 signal and homogeneously low ADC; IPT demonstrates mixed T2 signal and heterogeneous ADC. Delayed enhancement is less prominent in lymphoma.
Distinguishing Feature
Angiosarcoma typically shows more aggressive appearance, irregular margins, hemorrhagic components, and rapid progression. IPT is a well-circumscribed, stable lesion with delayed enhancement.
Distinguishing Feature
Metastasis typically presents as multiple lesions with known primary malignancy. IPT is typically solitary. Metastasis shows rim enhancement with central necrosis, while IPT demonstrates progressive delayed fill-in.
Distinguishing Feature
Hamartoma shows homogeneous T2 hyperintensity and homogeneous enhancement. IPT demonstrates mixed T2 signal and heterogeneous enhancement. Inflammatory markers are not elevated in hamartoma.
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
specialist-referralSplenic IPT is generally benign but cannot be reliably distinguished from malignant lesions on imaging. Definitive diagnosis typically requires histopathological examination after splenectomy. In ALK-positive cases, low malignant potential and local recurrence risk (5-10%) exist. Complete surgical resection is curative. Steroid-responsive cases have been reported — particularly in IgG4-related cases, steroids may be tried before surgery. In EBV-associated cases, long-term follow-up is recommended for lymphoproliferative disease monitoring.
Splenic IPT is a benign lesion but is difficult to distinguish from malignant lesions preoperatively. Splenectomy is usually required for both diagnosis and treatment. Recurrence is rare after complete resection.