Renal oncocytomas are both rare and benign. They can present with various symptoms, usually urological in nature. They are more prevalent in adults than in children, with a mean age of presentation within the 6th decade of life and peak incidence usually occursin the 7th decade of life (5). They are often discovered incidentally during clinical workups for non-urological issues in 56–91% cases (6). In symptomatic patients, hematuria, abdominal pain and a palpable mass are common in these patients (5, 6). They usually demonstrate as a unilateral solitary lesion. A small number of these tumors are bilateral or multifocal, 4–5% and 13% respectively (6).
Utilization of radiological imaging modalities including Ultrasonography, CT Scan and Magnetic resonance imaging (MRI), facilitate in the detection and diagnosis of these renal lesion (7).US picks up on these tumors and can show a well- demarcated mass with similar echogenicity to that of the rest of the kidney tissue(8). Grossly, on computed tomography oncocytomas are characteristically well-circumcised homogeneietyous mass with a sharp centrally located stellate scar, yet it is not pathognomonic. It is only appreciated in 33% of renal oncocytomas (7). Renal cell carcinoma may present with a central scar and other radiological features consistent with those of oncocytomas (8). A T1 signal for this tumor on MRI tends to be hypointense in comparison to the renal cortex, while it is often hyperintense on T2 weighted imaging(9). Radiological features are therefore suggestive of oncocytoma but cannot be definitively diagnostic, and sepcimens need to be sent for histological sampling.
Renal biopsies have a diagnostic accuracy rate of up to 80% (10). It cannot be relied upon fully because of limitations, such as the difficulty in distinguishing resembling variants of RCC (especially chromophobe subtype ), or the fear of missing out collision RCC or coexistent RCC at another affected site in within the kidney (10).
The neoplastic cells in this tumor are thought to originate from the renal intercalating cells of the collecting tubules. Macroscopically they are mahogany brown, contrary to RCCs which have a pale surface. Histopathologically renal oncocymoas consist of large differentiated pure oncocytes, an eosinophilic cytoplasm, which is granular due to the presence of abundant non-functional mitochondria. The nuclei in them are usually large and centrally located. Variation can also occur, i.e cellular atypia within the minority of specimens which possibly represents degeneration (10). Immunohistochemistry could be of help in the diagnosis. The International Society of Urological Pathology advocates the use of immunohistochemistry, in cases where the tumor appears to be borderline with malignant ones. Cytokeratin 7 is commonly used although it is positive only occasionally. CD117 stains are found to be positive and vimentin is negative in oncocytomas. These two stains work oppsitley in RCC, with Vimentin being positive and CD117 stains being negative. Cyclin D1, kidney-specific cadherin, S100A1 and E-cadherin can also be used to help identify and differentiate between oncocytomas and malignant tumors (11).
Generally, oncocytomas range between 0.6-14cms (12).The largest one identified to date was 27 cms in size as was reported by Demos et al(15). Literature search has revealed very few case reports on oncocymos with size greater than 14cm (12, 13).
Since there are no distinct presumptive findings for renal oncocytoma from a radiological point of view as well as clinical history, definitive diagnosis is usually reached after surgical removal (13). Radical nephrectomy is the mainstay treatment when there is uncertainty in distinguishing malignant versus benign tumor, size of oncocytoma is greater than 4cm or presence of concomitant RCC (14) . On the other hand, surveillance or partial nephrectomy should be applied for tumors of less than 4cm in size (5).
Learning points
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Educate surgeons for rare tumors presentation and management.
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Importance in differentiating between benign oncocytomas and RCC
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Importance of timely management of Oncocytoma