Bilateral Multifocal Renal Oncocytoma
Y. Mark Hong; Jeffrey B. Marotte, MD; Harcharan S. Gill, MD
Infect Urol 16(4):103-105, 2003. © 2003 Cliggott Publishing, Division of SCP Communications
Abstract and Introduction
The rarity of bilateral multifocal renal oncocytoma can pose a diagnostic challenge. Conservative surgical management (enucleation or partial nephrectomy) is the current standard of care.
Renal oncocytomas account for approximately 5% of all primary renal neoplasms. Bilateral oncocytomas represent 5% of all renal oncocytomas, while multifocal bilateral oncocytomas represent only 1.4%. The standard of care continues to be conservative surgical management, with enucleation of this benign tumor or partial nephrectomy rather than radical nephrectomy.
A renal oncocytoma is an epithelial tumor thought to arise from proximal tubular or intercalated cells of collecting ducts. The tumor consists of large eosinophilic cells with small round nuclei. Most authorities consider renal oncocytomas benign.
Most oncocytomas are unilateral and are not rare. Bilateral oncocytomas, however, are unusual, and bilateral multifocal oncocytomas are very rare. We present a case of bilateral multifocal renal oncocytomas and review the management of these tumors.
A 60-year-old woman presented with vague lower abdominal discomfort. The patient had a history of hypercholesterolemia but no family history of renal cancer. She was a lifetime nonsmoker. She reported no hematuria, weight loss, or back pain. Findings from the physical examination were unremarkable, with normotensive blood pressure and no abdominal tenderness or palpable masses. Lab oratory data included a serum creatinine level of 1 mg/dL, a hemoglobin level of 12.8 g/dL, and normal urinalysis results.
Abdominal ultrasonography revealed an incidental left renal mass, which prompted further evaluation with CT. An abdominal CT scan demonstrated bilateral renal masses, with an 8 × 8-cm mass in the left lower pole and a 1.5-cm mass in the right upper pole, as well as a 3.7-cm mass in the right lower midmedial area (Figure 1). The CT appearance was consistent with either renal cell carcinoma or oncocytoma. The workup for metastasis yielded negative results.
The patient subsequently underwent a left partial nephrectomy. At surgical exploration, the left renal mass, which was firm, smooth, and well-circumscribed, was found to be in the interpolar region involving the collecting system. Pathologic evaluation of a frozen section of the mass revealed oncocytoma with negative surgical margins. The final diagnosis, based on pathologic examination, concurred. The patient made an uneventful recovery from this surgery.
Four months later, the patient underwent an elective right partial nephrectomy with excision of a well-circumscribed, reddish brown, upper pole anterior lesion and a soft, brown, lower pole posterior lesion. The final pathologic diagnosis confirmed that both lesions were renal oncocytomas (Figure 2). The patient's creatinine level increased to a high of 2 mg/dL before stabilizing at about 1.8 mg/dL. She was discharged to home on postoperative day 4.
While Zippel mentioned the first case of renal oncocytoma in 1942, the 1976 report by Klein and Valensi of 13 cases gained oncocytomas widespread attention in the literature. Since then, several studies and case reports have been published on renal oncocytomas. The incidence of renal oncocytoma has generally been reported as approximately 5% of primary renal neoplasms.[3-6] A recent series of 138 tumor specimens showed a renal oncocyto ma incidence of 10%; this percentage increased to 18% when only renal lesions 4 cm or smaller were considered. Mean tumor diameters have ranged from 4.4 to 8.1 cm, with 68% of tumors 4 cm or smaller in the same series.
Bilateral oncocytomas are rare, with a 5% incidence among renal oncocytomas.[5,6] Bilateral multifocal renal oncocytomas are even more rare, with a reported incidence of 1.4% and fewer than 20 other cases reported in the literature to date.[7-11]
Bilateral multifocal oncocytomas continue to pose a diagnostic challenge. It has been well established that a CT scan cannot distinguish between renal oncocytoma and renal cell carcinoma despite certain distinguishing features of oncocytoma, such as central stellate scars. Diagnostic difficulty is confounded by the fact that renal carcinoma has been reported to coexist with renal oncocytoma in 7.2% to 32% of cases.[6,13,14]
There is still insufficient evidence of the malignant potential of renal oncocytoma. Previously reported cases of malignancy may have been chromophobe renal cell carcinoma instead of renal oncocytoma. Therefore, treatment is best approached conservatively, with enucleation or nephron-sparing surgery being the first surgical option. While cases in which CT-guided or open biopsy without surgical tumor removal was used have been reported, no long-term follow-up has been reported for observation only. In cases of coexistent renal cell carcinoma or end-stage renal disease, bilateral radical nephrectomy has been performed.
Our patient underwent staged partial nephrectomies with preservation of adequate renal function. While there has not been sufficient postnephrectomy follow-up time in which to observe the patient, others have reported near 100% cure without tumor progression at up to 200 months of follow-up,[5,6] further typifying the benign nature of renal oncocytoma.
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Editorial Comment: Need for Sparing Surgery
This article draws attention to a somewhat rare clinical situation. Because oncocytomas have such low metastatic potential, urologists should be alert to the condition in an effort to spare functional renal tissue whenever possible. As the article illustrates, clinicians cannot rely on preoperative radiographic technology to make a definitive diagnosis.
Marc S. Cohen,
Hong, Jeffrey B.
Marotte, MD, Harcharan S. Gill, MD, Stanford University School
of Medicine, Stanford, Calif