Giant renal oncocytoma masquerading as infiltrating renal cell carcinoma: case report and literature review

Renal oncocytomas (RO) are tumours containing a population of cells with highly differentiated eosinophilic granular cytoplasm, extremely rich in mitochondria. It is estimated they account for about 3 to 7% of all solid renocortical tumours that were previously regarded as renal cell carcinoma. Based on their clinical behaviour and distinct pathologic features they are now regarded as benign renal tumours, often less than 5cm in diameter. We present a case of giant renal oncocytoma in a patient with synchronous bladder tumour, with pre-operative clinical, urographic and ultrasound features of locally advanced renal cell carcinoma (RCC). Findings at surgery included huge right renal tumour with infiltration to the duodenum; hepatic colic flexure; gall bladder; liver capsule and the greater omentum with small indurations at the base of the bladder. There was no tumour extension to the renal vein, no peritoneal seedling, no nodal metastasis and no ascites. Radical nephrectomy was carried out with good prognosis and without recurrence 52months post nephrectomy. This presentation, besides highlighting the possible giant nature of RO, also illustrates the malignant potential of RO to infiltrate contiguous structures and mimics infiltrating RCC. In view of the difficulties at establishing pre-operative diagnosis in this disease and because nephron-sparing surgery is curative, especially for the well-circumscribed tumours, RO should be considered in the management of patients with features of infiltrating RCC. A review of literature is also presented.