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Because several features of renal oncocytoma overlap those of other renal neoplasms including chromophobe renal cell carcinoma (cRCC), a subtype of renal cell carcinoma, strict diagnostic criteria for differentiating between them have not been clearly defined. Between 1974 and 2001, nephrectomy was performed in 796 cases diagnosed as renal epithelial neoplasms at our department. The pathological diagnosis was cRCC in 15 of them, renal oncocytoma in eight of them. We performed a retrospective study to determine the utility of peanuts agglutinin (PNA), dolichos biflorus agglutinin (DBA), leu M1 (LM1), colloidal iron staining and CD68 staining, in addition to the conservative HE method, to define the histological criteria for the diagnosis of these tumors. PNA staining, DBA staining, and LM1 staining were similarly positive, and there were no significant differences between renal oncocytoma and cRCC. By contrast, using CD68 staining, the cRCCs had a high positive rate of 80% (12/15), but only one of the eight cases (12.5%) was positive. A high proportion of cRCCs stained positive with the macrophage marker CD68 antibody, suggesting that immunohistostaining for CD68 is helpful in making the differential diagnosis between cRCC and renal oncocytoma.

We report a case of renal oncocytoma associated with acquired cystic disease of kidney (ACDK). A right renal mass was incidentally found on an annual ultrasonography of the kidneys in a 56-year-old female patient who had been on maintenance hemodialysis for 6 years. Computerized tomography (CT) showed a right hypervascular renal mass, suggesting a renal cell carcinoma associated with ACDK. Right radical nephrectomy was performed. The post-operative pathological diagnosis was renal oncocytoma. Renal oncocytoma in ACDK is very rare, and the pathological characteristics of oncocytoma are discussed.

A case of renal oncocytoma found incidentally by routine medical checkups is reported. An asymptomatic 70-year-old male was found to have a right renal mass by abdominal ultrasonography. Selective renal arteriography supported the diagnosis of renal oncocytoma with a typical appearance of "spoke-wheel" pattern. Right radical nephrectomy was performed. However, in consideration of the possibility of renal cell carcinoma. The diagnosis of renal oncocytoma was finally confirmed pathologically. The present case represents the 58th renal oncocytomas reported in Japan as of December 1992.

Two cases of renal oncocytoma are reviewed. A 67-year-old man and a 21-year-old man with a right renal mass were incidentally revealed by echography. Selective renal angiogram showed no spoke-wheel configuration of vessels in either case. Both cases were pathologically diagnosed as oncocytomas, constructed of large eosinophilic cells with granular cytoplasm and small regular nuclei. The electron micrograph showed cytoplasm packed abundantly with mitochondria. The two patients are in good condition 2.5 and 1.5 years after diagnosis.

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.

A case of a renal oncocytoma associated with tuberous sclerosis in a 31-year-old woman is reported. She displayed many characteristic skin features of tuberous sclerosis but no central nervous symptoms. Although she complained of dysmenorrhea and hypermenorrhea, she had no complaints related to the kidney. A left renal tumor was discovered incidentally during preoperative examination for gynecologic disease and left nephrectomy was performed. Histologically, the tumor was shown to be a typical renal oncocytoma. This is supposed to be the first case of renal oncocytoma associated with tuberous sclerosis in Japan.

We report a case of renal oncocytoma and review 158 cases in the literature. The patient was a 75-year-old woman whose chief complaint was epigastric discomfort without any urological symptoms. The right renal tumor was incidentally discovered by ultrasonography. Its angiographic patterns such as spoke-wheel appearance and homogeneous nephrogram were "characteristic" of renal oncocytoma. We diagnosed it as oncocytoma by microscopical and ultrastructural observation.