A Rare Case of Primary Follicular Dendritic Cell Sarcoma of the Kidney.

The objective of this case report is to describe a rare case of primary follicular dendritic cell sarcoma (FDCS) of the kidney. FDCS is a rare soft tissue malignancy that most often presents intranodally with lymphadenopathy of the neck, mediastinum, and axilla. One-third of cases present extranodally and most commonly affect the liver, lung, and tonsils. To date, there have been few reports of retroperitoneal FDCS and, to the best of our knowledge, only two other reported cases with primary renal involvement. We present a 56-year-old female with end-stage renal disease on hemodialysis who presented to the hospital with a hypertensive emergency. Computed tomography (CT) of the abdomen was obtained revealing a left-sided renal mass and she subsequently underwent left radical nephrectomy. The pathologic features of the mass revealed oval to spindle cells with eosinophilic cytoplasm, dispersed vesicular chromatin, and small nucleoli found arranged in fascicles, whorls, and storiform patterns with occasional multinucleate forms. The neoplastic cells were immunoreactive to vimentin and expressed cell markers for CD23, CD35, and CD68. These features confirmed a final pathologic diagnosis of primary FDCS of the kidney. To our knowledge, this is the third case of primary renal FDCS reported in the literature. Extranodal FDCS is rare but does occur and needs to be on the differential diagnosis if pathologic features point to its diagnosis.