Figure 1.

A. Characteristic gross appearance of renal oncocytoma - well circumscribed, mahogany brown tumor with a central scar. Histology: B. Typical oncocytoma composed of nests and acini of polygonal to round oncocytes with abundant densely granular eosinophilic cytoplasm and round nuclei embedded in loose myxoid or hyalinized stroma surrounded by a delicate reticulin framework (classic organoid pattern). C. Closely packed cystically dilated tubules seen in the tubulocystic pattern. D. Mixed pattern. E. Solid pattern with compactly arranged nests or sheets of oncocytes posed the biggest diagnostic challenge, especially in cases with its predominance. F. Typical oncocytes with abundant granular eosinophilic cytoplasm and round nuclei with smooth contours and small nucleoli.