Mitochondria with tubulovesicular cristae in renal oncocytomas

Renal oncocytoma and chromophobe renal cell carcinoma (CRCC) are closely related tumors. They are considered the extremes of a spectrum with several variants. Ultrastructural examination of the mitochondria is a helpful procedure in the diagnosis of these neoplasms. Renal oncocytomas show mitochondria with piled lamellar cristae, and CRCC exhibited mitochondria with tubulovesicular cristae. In a series of 23 histologically diagnosed renal oncocytomas examined by electron microscopy, the authors found 5 tumors exhibiting more cells with mitochondria showing tubulovesicular cristae. The authors believe these 5 cases present a submicroscopic appearance intermediate between renal oncocytoma and CRCC, although with benign clinical behavior.