Diagnosis

Diagnosis

Renal Oncocytoma

Discussion

The gross photo demonstrates a well-circumscribed, red-brown mass with a central stellate scar within the renal cortex. Oncocytoma is a benign renal neoplasm composed of nests or solid sheets of mitochondria-rich eosinophilic cells, which impart a "mahogany brown" color to the tumor macroscopically. These tumors demonstrate a central scar in approximately 50% of cases, particularly larger examples.

The main tumor in the gross differential diagnosis of oncocytoma is renal cell carcinoma (RCC). Conventional clear cell RCC typically has a golden yellow color with areas of hemorrhage and/or necrosis. Chromophobe RCCs are tan-brown and may have areas of hemorrhage and/or necrosis. Papillary RCCs are brownish in color (due to hemosiderin deposition and not mitochondria-rich cells) and may be very soft and friable. Sarcomatoid transformation in RCC will appear as gray-white, firm, or fleshy foci with hemorrhage and/or necrosis. Some helpful macroscopic clues in this differential diagnosis include the lack of a central scar in RCC and the lack of necrosis in oncocytoma, although hemorrhage may be seen in both. 

References

Susan C. Lester, Manual of Surgical Pathology, 3rd Edition. W.B. Saunders, 2010.

WHO Classification of Tumours Editorial Board. Urinary and Male Genital Tumours. Lyon (France): International Agency for Research on Cancer; 2022. WHO Classification of Tumours Series, 5th Edition; Volume 8.
 

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