EBV-positive inflammatory follicular dendritic cell sarcoma with extensive epithelioid granulomas: 2 splenic case reports and literature review

Epstein-Barr virus-positive inflammatory follicular dendritic cell sarcoma (EBV + IFDCS) is a rare indolent malignancy of neoplastic follicular dendritic cell (FDC) proliferations in a background of lymphoplasmacytic infiltrates. The broad spectrum of morphology and inconstant immunophenotype compound the difficulty in diagnosis. Herein we report 2 splenic cases of EBV + IFDCS mimicking granulomatous inflammation morphologically and with discrepant immunophenotypes, incurring misdiagnosis. Two male patients, aging 59 and 62 respectively, with splenic mass found incidentally on radiological examination. Splenectomy was performed. Pathologic examination showed similar histologic features: extensive epithelioid granulomas of various size dispersed in a heavy background of lymphoplasmacytic cells, within them, mildly atypical spindle to oval cells were distributed subtly or arranged in loose fascicles, with indistinct cell borders, delicate nuclear membranes, vesicular chromatin and small distinct nucleoli. Immunohistochemistry showed the atypical cells were negative for FDC markers(CD21, CD23, CD35, D2-40, CXCL13 and clusterin) but positive for smooth muscle actin(SMA) in case 1, while case 2 showed diffuse SMA and focal CD35 positivity. EBV-encoded RNA(EBER) in situ hybridization labeled the atypical cells in both cases. Hence, the diagnosis of granulomatous variant of EBV + IFDCS was concluded. Follow-up data showed no recurrence or metastasis. Granulomatous variant of EBV + IFDCS mimics inflammatory lesions morphologically. Identification of EBV associated FDC-like cell proliferation helps make the distinction. The immunophenotype of lacking FDC markers expression but showing SMA positivity suggests a proliferation of fibroblastic cell lineage other than FDC.