Splenic IPT consists of with bland spindle cells with a mixture of lymphocytes, histiocytes, plasma cells. The spindle cell proliferation is obscured by the sclerosis and have characteristics of myofibroblasts.
Lymphocytes, plasma cells, eosinophils and neutrophils are evident. The spindle cells may be positive for EBV in splenic IMTs.
The stroma can be quite sclerotic, more sclerotic than inflammatory pseudotumors or inflammatory myofibroblastic tumors found in other sites.
The hyalinized and sclerotic stroma here is quite pronounced.
The occurrence inflammatory pseudotumor (IPT) in the spleen is extremely rare with only sporadic case reports and small case series. In contrast to those occurring in other sites, those in the spleen and liver are often associated with Epstein–Barr virus (Neuhauser, Lewis, Rosenbaum).
Some authors use the term inflammatory myofibroblastic tumors (IMT) for all entities previously described as inflammatory pseudotumor and plasma cell granulomas. However, some experts prefer to reserve IMT for tumors demonstrating the ALK translocation and employ IPT for those lesions with identical histology but lack the ALK translocation. As such, the studies performed on splenic inflammatory pseudotumor thus far have not shown the ALK translocation, but rather, an association with EBV. Thus, the term splenic inflammatory pseudotumor is often used instead of splenic inflammatory myofibroblastic tumor.
The finding of EBV in splenic IMT can be variable, however. Neuhauser et al (2001) found that out of 12 cases of splenic IMT, 6 were EBER positive. In contrast, Kutok et al (2001) studied 13 cases of IMT (9 involving the lymph node and 4 involving the spleen) and found that only one lymph node IMT was focally positive for EBER. All 13 cases were negative for the ALK translocation and HHV8.
Grossly, the tumor is firm, white and circumscribed. Histologically, there is a proliferation of spindle cells admixed with a prominent infiltrate of lymphocytes, plasma cells, scattered eosinophils and neutrophils. Compared to other sites, splenic inflammatory pseudotumor tends to have a more sclerotic stroma (Fletcher). The spindle cells are usually reactive for SMA and vimentin and focally reactive for CD68 (Neuhauser, Kutok). Some have found markers for follicular dendritic cells in the spindle cell component, while others have shown the lack of these markers.
In a study of 12 splenic IMTs, the majority (9 cases) presented with abdominal pain and fever (Neuhauser). On imaging, most cases demonstrate solitary relatively large well-circumscribed splenic masses.
Excision is generally curative.
Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 1307-8.
Kutok JL, Pinkus GS, Dorfman DM, Fletcher CD. Inflammatory pseudotumor of lymph node and spleen: an entity biologically distinct from inflammatory myofibroblastic tumor. Hum Pathol. 2001 Dec;32(12):1382-7.
Lewis JT et al. Inflammatory pseudotumor of the spleen associated with a clonal Epstein-Barr virus genome. Case report and review of the literature. Am J Clin Pathol. 2003 Jul;120(1):56-61.
Neuhauser TS, et al. Splenic inflammatory myofibroblastic tumor (inflammatory pseudotumor): a clinicopathologic and immunophenotypic study of 12 cases. Arch Pathol Lab Med. 2001 Mar;125(3):379-85.
Rosenbaum L, Fekrazad MH, Rabinowitz I, Vasef MA. Epstein-Barr virus-associated inflammatory pseudotumor of the spleen: report of two cases and review of the literature. J Hematop. 2009 Mar 31. [Epub ahead of print]