Splenic Inflammatory Pseudotumor



Splenic Inflammatory Pseudotumor


Roberto N. Miranda, MD










CT of abdomen shows a normal-sized spleen image with a 2.5 cm in diameter inflammatory pseudotumor image. Lesion was 1 cm 16 months before, when it was found during staging for renal cell carcinoma.






Splenic inflammatory pseudotumor shows a well-circumscribed fleshy mass with focal hemorrhage surrounded by congested splenic parenchyma.


TERMINOLOGY


Abbreviations



  • Splenic inflammatory pseudotumor (IPT)


Definitions



  • Reactive lesion of spleen composed of inflammatory cells and spindled cells with or without sclerosis


  • Etiology of splenic IPT is unknown


  • Classification is controversial since other entities have been classified as IPT; in particular



    • Inflammatory pseudotumor-like follicular dendritic cell tumor (IPT-FDCT)



      • True neoplasm that involves mainly liver and spleen


    • ALK(+) inflammatory myofibroblastic tumor (IMT)



      • Most often involves soft tissues of children and young adults


    • IPT-FDCT and ALK(+) IMT are now excluded from the category of IPT


ETIOLOGY/PATHOGENESIS


Infectious Agents



  • Etiology of splenic IPT is unknown


  • Most likely a number of causes may ultimately result in splenic IPT



    • Infectious causes are likely



      • Variable association reported with Streptococcus, Legionella, and Epstein-Barr virus


    • Vascular events may be involved


    • Autoimmunity has been hypothesized to play a role


  • Regardless of initiating event, exuberant tissue repair is probably involved in pathogenesis


  • Splenic IPT appears to be pathobiologically similar to IPT of lymph nodes


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Uncommon; ˜ 3% of splenic masses


    • Rare when compared with IPT at other sites of body


  • Age



    • Range: 19-87 years; median: 53 years


    • Rare in children


  • Gender



    • Slight female predominance; M:F ratio = 1:1.3


Site



  • Typically involves spleen as single lesion



    • Rare cases can be multicentric


Presentation



  • Affected patients are immunocompetent


  • Fever and weight loss in about half of patients


  • Asymptomatic in 50% of cases


  • Epigastric or left flank pain, usually associated with larger lesions



    • Splenomegaly may be noted in some cases


  • Occasional IPT are associated with malignancies, e.g., colon or renal cell carcinoma


Laboratory Tests



  • Usually unremarkable



    • Occasionally patients have mild leukocytosis, (< 15 x 109/L), anemia, and hypergammaglobulinemia


Treatment



  • Due to rarity and nonspecific CT or MR imaging, these lesions are not diagnosed preoperatively



    • Diagnosis first established after splenectomy



      • Splenectomy is effective treatment


  • Symptoms and laboratory abnormalities disappear after splenectomy



Prognosis



  • Excellent prognosis; no deaths attributable to splenic IPT


  • Tumors are cured by splenectomy, and there are no reported recurrences of similar lesions elsewhere


IMAGE FINDINGS


CT Findings



  • Discrete, single splenic mass


  • Associated with splenomegaly when tumors are larger


  • Lymphadenopathy is unusual


MACROSCOPIC FEATURES


General Features



  • Spleen weight



    • Mean: 331 g (range: 140-1,030 g)



      • Splenomegaly > 250 g in 50% of cases


  • Well-circumscribed, nonencapsulated single mass



    • Cut surface is white-tan, gray, or yellow; soft to firm lesions


    • Rarely multinodular


    • Mean size: 10 cm (range: 1-22 cm)


MICROSCOPIC PATHOLOGY


Histologic Features



  • Lesions are usually well circumscribed



    • Lesions may be partially encapsulated


    • Islands of white or red pulp may be trapped at periphery of lesion


  • 3 growth patterns are recognized; may occur simultaneously



    • Cellular spindle cell, composed of short fascicles



      • Most common


      • Can be focally storiform; rare mitoses identified


      • Bland spindle cells with oval vesicular nuclei and small nucleoli


    • Hypocellular fibrous pattern, similar to scar tissue


    • Myxoid and vascularized, similar to granulation tissue


  • Abundant mixed inflammatory infiltrate of plasma cells, lymphocytes, and histiocytes



    • Variable proportions of inflammatory cells in different areas of same lesions



      • Marked variability from case to case


    • Lymphocytes are usually small with occasional immunoblasts


    • Mature plasma cells, with occasional Russell bodies


  • Other features



    • Focal, central necrosis usually associated with neutrophilic infiltrate



      • Histiocytes and eosinophils are less frequent


    • Hemorrhage and hemosiderin deposition


  • Compressed and congested splenic parenchyma around tumor; otherwise unremarkable spleen


ANCILLARY TESTS


Immunohistochemistry



  • Spindle cells



    • Vimentin(+) and CD68([+], focal)


    • ˜ 70% of cases are positive for smooth muscle actin (focal) and desmin(-)



      • Smooth muscle actin(+) cells are considered myofibroblasts


    • Occasionally positive for S100 protein (focal) and Factor XIII


    • CD8(-), CD21(-), CD23(-), and CD30(-)


    • HMB-45(-), ALK-1(-), HHV8(-), and cytokeratin(-)


    • Epstein-Barr virus(+) in small subset of cases



      • Infected cells are spindle cells, some of which can focally express smooth muscle actin


  • Lymphocytes and plasma cells



    • Mixture of T and B cells; usually with predominance of CD3(+) cells


    • B cells and plasma cells are polytypic



Cytogenetics



  • Normal karyotype


Molecular Genetics



  • No evidence of monoclonal immunoglobulin (Ig) or T-cell receptor gene rearrangements


  • No known oncogene abnormalities


DIFFERENTIAL DIAGNOSIS


Inflammatory Pseudotumor-like Follicular Dendritic Cell Tumor (IPT-FDCT)



  • Female predominance


  • Considered variant of follicular dendritic cell sarcoma


  • More aggressive clinically, contrary to splenic IPT



    • Recurrences are common


    • Recurrent tumors show pleomorphic large cells usually not detected in primary tumors


  • Immunohistochemistry helpful as FDC can be



    • CD21(+), CD23(+), Factor XIII(+)


  • Commonly EBV(+)



    • Monoclonal EBV when assessing EBV DNA terminal repeat regions


  • IPT-FDCT of spleen is pathobiologically similar to liver IPT


Inflammatory Myofibroblastic Tumor (IMT)



  • Affects soft tissues of children and young adults


  • Ill-defined mass grossly


  • Myofibroblasts positive for smooth muscle actin (100%) and cytokeratin (15-30%)



    • Negative for follicular dendritic cell markers and H-caldesmon


  • Scattered large atypical cells, sometimes ganglion-like cells with prominent nucleoli


  • Harbors balanced translocations involving anaplastic lymphoma kinase (ALK) gene at 2p23



    • Anaplastic lymphoma kinase (ALK) is expressed in ˜ 50% of cases


    • ALK is not expressed in splenic IPT


  • Has locally aggressive clinical behavior with recurrences


  • Rare reports of IMT in spleen, but those reported have been ALK(-)


Follicular Dendritic Cell Sarcoma (FDCS)



  • Formerly designated as follicular dendritic cell tumor


  • Affects primarily lymph nodes but can involve spleen and other sites



    • Intraabdominal cases are often clinically aggressive


  • More aggressive than IPT-FDCT, with recurrences and distal metastasis


  • No gender predilection, except in splenic or hepatic forms where there is female predominance


  • FDCS can show range of histologic features



    • Composed of spindled or epithelioid cells


    • Bland or pleomorphic cytologic features


    • May display scattered inflammatory cells


  • Immunohistochemistry helpful as FDCS can be



    • CD21(+), CD23(+), CD35(+), CNA.42(+)


    • Clusterin(+), fascin(+), and EGFR(+)


  • Rare or no association with EBV


Inflammatory Pseudotumor (IPT) Involving Other Sites



  • Usually present with systemic findings; sometimes asymptomatic


  • IPT has been diagnosed in various anatomic sites



    • Respiratory tract, lungs, orbit, spinal meninges, digestive tract, heart, and lymph nodes


  • Encompasses lesions where myofibroblasts are detected but are not main component



    • Variable mix of small and activated lymphocytes


    • Polytypic plasma cells, histiocytes, and sclerosis


  • Fibrotic process in lymph node extends along capsule or trabeculae and then throughout parenchyma


  • EBV small encoded RNA (EBER)(+) in 20% of nodal IPT; in scattered lymphocytes



    • Spindle cells are negative for EBER


Sclerosing Angiomatoid Nodular Transformation (SANT)



  • Involves splenic red pulp


  • Recently described entity with overlapping features with splenic IPT



    • Some researchers consider that SANT is subset or end stage of splenic IPT


  • Single mass composed of multiple small nodules


  • Nodules display dense network of capillaries as well as remnants of sinuses



    • Endothelial cells positive for CD34 and CD31; usually negative for CD8


    • EBER(-); EBV latent membrane protein type 1(-)


    • Negative for follicular dendritic cell markers CD21, CD35, and CNA.42


  • Collagenous fibrosis with scattered spindle cells may occur around and in center of lesion



    • Spindle cells around nodules react as myofibroblasts and are smooth muscle actin(+)


  • Angiomatoid nodules occasionally show dense inflammatory infiltration



    • Polytypic plasma cells, small lymphocytes, and histiocytes are not unusual


  • Hyalinization of arterial walls and organizing thrombosis in veins


Splenic Hamartoma

Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Splenic Inflammatory Pseudotumor

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