Unusual eosinophilic variant of chromophobe cell renal carcinoma--an ultrastructural diagnosis

A case of eosinophilic variant of chromophobe cell renal carcinoma (EVCCRC), an uncommon variety of renal cell carcinoma, occurred in a 72 year old male. The most problematic differential diagnosis was renal oncocytoma, as the two entities share overlapping features on histology, yet differ completely in biological behavior. EVCCRC is a potentially malignant neoplasm whereas renal oncocytoma is totally benign. Staining with Hale's Colloidal Iron using modified Mowry's technique showed granular cytoplasmic positivity. The diagnosis was confirmed by ultrastructural examination of the tumor which revealed unique features of EVCCRC like presence of numerous cytoplasmic microvesicles along with mitochondria displaying tubulo-vesicular cristae. This case delineates the role of electron microscopic examination as the sole means to differentiate EVCCRC from renal oncocytomas.