SOLITARY FIBROUS TUMOR OF THE KIDNEY

A 28-year-old woman was admitted to the hospital with a 4-year history of abdominal pain. Other symptoms, including hematuria, were not present. Physical examination revealed a left abdominal mass. Computerized tomography revealed enlargement of the left kidney, with an irregular hypodense and heterogeneous area, which had displaced adjacent organs. Radical nephrectomy was performed. The kidney measured 16 3 12.5 3 6 cm. On cut section a 15 3 11 cm. firm, greyish-white tumor had replaced almost the entire kidney (fig. 1). Microscopically, the tumor was well circumscribed and involved the renal capsule but not the renal pelvis. In most histological fields the mass showed parallel bundles of collagen and bland spindle-shaped cells with fusiform or ovoid nuclei and scanty cytoplasm (fig. 2, A). In other areas storiform or stream patterns with or without myxoid changes were noted (fig. 2, B). Mitoses were virtually absent. Immunohistochemical stains were strongly positive for CD34 and vimentin and negative for S-100 protein, keratin, desmin, smooth muscle actin and epithelial membrane antigen. At