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Splenic inflammatory pseudotumor (IPT) is an uncommon lesion with an inflammatory morphologic aspect that often poses a diagnostic challenge. The etiology of IPT can be infectious, autoimmune, reactive, or neoplastic. Splenic Epstein-Barr virus (EBV)-associated IPTs form a subset of splenic IPTs in which there is a spindle cell component infected by EBV. The best characterized and most frequent subgroup of splenic EBV-associated IPT is IPT-like follicular dendritic cell tumor. This review also focusses on EBV-associated splenic IPTs without follicular dendritic cell marker expression. These lesions are less well characterized, making the differential diagnosis with other splenic lesions even more difficult. Recently, increased numbers of immunoglobulin G4-positive plasma cells and the presence of numerous granulomas have been reported in EBV-associated IPTs, and this can add to the difficulties in recognizing the neoplastic nature of these lesions. Herein, we also review the epidemiology, clinical features, histologic morphology, immunohistochemistry, electron microscopy, and pathogenesis of EBV-associated IPTs.

Follicular dendritic cell sarcoma is a rare tumor that typically arises within lymph nodes but can also occur extranodally. It is important to have a high index of suspicion, so follicular dendritic cell sarcoma is included in the differential diagnosis of a spindle cell neoplasm in the appropriate clinical and morphologic settings. When included in the differential diagnosis, immunohistochemistry is generally sufficient to substantiate the diagnosis of follicular dendritic cell sarcoma. In this review, we discuss the clinicopathologic features of follicular dendritic cell sarcoma, recent molecular and cytogenetic findings, prognosis, and current approaches to treatment.

Follicular dendritic cell sarcoma is an uncommon neoplastic proliferation of spindled to ovoid cells with morphologic and immunophenotypic features similar to normal follicular dendritic cells. While most follicular dendritic cell sarcomas arise from lymph nodes, at least one-third occur in extranodal sites. A broad differential diagnosis can be developed--as this tumor has morphologic features similar to other tumors, hence creating a diagnostic pitfall--but its immunophenotypic profile is quite specific and is diagnostically crucial. Herein, we review the pathogenesis; histologic morphology; and immunohistochemical, electron microscopy, and clinical features, including treatment and prognosis, of follicular dendritic cell sarcomas. We will briefly describe the role of molecular studies including utility of BRAF mutations in diagnosing this tumor.

Extranodal follicular dendritic cell sarcoma is a rare tumor of follicular dendritic cells that can occur in a wide variety of sites. Although fairly well characterized histologically, with a distinct immunophenotype, it remains under-recognized, with as many as one third of cases initially misdiagnosed. This is often due to a failure to consider the entity. Patients with this tumor may have a worse prognosis than originally described. Prompted by a recent case at our institution, we briefly review the clinical features, etiology, histologic, and cytologic appearance of the tumor, as well as the ancillary studies useful in resolving diagnostic issues, primarily in an attempt to increase recognition of this rare neoplasm.