[Renal hemangiopericytoma: report of a case].

A 34-year-old house wife presented with a right renal mass detected by work-up for epigastralgia. The mass located in the right renal sinus was round and approximately 3 cm in diameter. Although the tumor was well enhanced with contrast medium on CT scan, it was hypovascular on the early arterial phase of renal angiography. Translumbar radical nephrectomy was performed on suspicion of the right renal cell carcinoma. The tumor was solid and hard and, the cut surface of the tumor was homogenously colored pale pink. Microscopically it was hemangiopericytoma arising in the renal sinus, composed of well-developed pericytes and capillaries with so-called staghorn configuration, with invasion of hilar renal vein. Immunohistochemically, the hemangiopericytes were strongly positive for CD34, but negative for factor VIII associated antibodies. To our knowledge, the present patient is the 6th case in the Japanese literature and the first case with incidentally detected renal hemangiopericytoma.