[Inflammatory pseudotumor-like follicular dendritic cell tumor of spleen]

To study the clinicopathologic features of inflammatory pseudotumor-like follicular dendritic cell tumor of spleen.

One case of inflammatory pseudotumor-like follicular dendritic cell tumor of spleen was examined macroscopically and microscopically. Immunohistochemical study for CD21, CD23, CD35, clusterin, S-100 protein, vimentin, smooth muscle actin, CD1a, CD68, ALK protein, CD30, CD31, CD34, CD3 and CD20 was performed on formalin-fixed, paraffin-embedded sections by standard EnVision method. In-situ hybridization for Epstein-Barr virus (EBV)-encoded RNA was also carried out.

Macroscopically, inflammatory pseudotumor-like follicular dendritic cell tumor was large in size, tan-colored, soft to rubbery in consistance and associated with central hemorrhage and necrosis. Histological examination showed scattered follicular dendritic cells admixed with abundant lymphocytes and plasma cells in the background, simulating inflammatory pseudotumor. On high-power magnification, the follicular dendritic cells possessed a moderate amount of pale to lightly eosinophilic cytoplasm, with indistinct cell borders. The nuclei were ovoid or spindly, with vesicular or stippled chromatin and small distinct, often centrally located, nucleoli. Some of the tumor cells showed nuclear pleomorphism and contained irregular foldings of nuclear membrane, coarse chromatin and prominent eosinophilic nucleoli. Mitotic figures were rarely identified. Immunohistochemical study showed that the tumor cells were positive for vimentin, clusterin, smooth muscle actin and CD68. They were weakly and focally positive for CD35 and S-100 protein, but negative for CD21, CD23, CD1a, ALK protein, CD30, CD31 and CD34. Most of the background lymphocytes were of T-lineage (CD3-positive) ,some were CD20 (B-cell marker)-positive. EBV RNA was demonstrated in the tumor cells by in-situ hybridization analysis.

Inflammatory pseudotumor-like follicular dendritic cell tumor is a rarely encountered low-grade malignancy with distinctive morphologic pattern. It is associated with EBV infection.