EBV-positive inflammatory follicular dendritic cell sarcoma of fibroblastic reticular cell phenotype arising in intrapancreatic accessory spleen.

Epstein-Barr Virus (EBV)-positive inflammatory follicular dendritic cell sarcoma (EBV-IFDCS) is a rare tumor of low malignant potential. Abundant lymphocytes and plasma cells often infiltrate into this tumor tissue with lymphoid follicles and sarcoid-like granulomas, so that the differential diagnosis of this tumor includes inflammatory lesions such as IgG4-related disease, morphologically. This tumor typically arises in the spleen or liver, and shows follicular dendritic cell (FDC)-like immunophenotype. Here we presented a case of EBV-IFDCS arising in intrapancreatic accessory spleen, which was preoperatively considered as a pancreatic tumor. Immunohistochemistry revealed its fibroblastic reticular cell-like phenotype, namely alpha SMA, l-caldesmon, tenascin C, and transglutaminase II positivity, while FDC marker expression such as CD21 and clusterin was focal. Positivity for EBV-encoded small RNA in situ hybridization (EBER ISH) distinguished it from inflammatory lesions or conventional FDC sarcoma. The differential diagnosis of EBV-IFDCS is broad, ranging from non-neoplastic lesions to sarcoma, particularly when it arises in unusual sites. Therefore, careful gross and microscopic examination and adequate immunohistochemistry application including EBER ISH are important to diagnose it properly.