[A case of renal oncocytoma].

A case of renal oncocytoma is reported. A 56-year-old woman was admitted with the complaint of an abdominal mass. Right transabdominal nephrectomy was performed on January 23, 1984. The resected kidney weighed 262 g and contained a well-demarcated 5 X 5 X 4 cm tumor in the middle portion. The cross section of the tumor was tan-brown. Light microscopic examination disclosed that the greater part of the tumor was composed of cells with abundant, and finely granular eosinophilic cytoplasm and with moderate nuclear pleomorphism. Electron microscopic examination confirmed that the cytoplasm had numerous mitochondria and few other organelles. According to these findings, the tumor was diagnosed as renal oncocytoma. Furthermore, it is noteworthy that in this case there were tubular arrangement of the cells resembling proximal renal tubules in a focal area and a group of cells with considerable nuclear atypia and hyperchromatism in another area. The patient has been well without any local recurrence or distant metastasis ten months after the operation. In addition, fourteen cases of renal oncocytoma in Japan, including the present case, are reviewed.