Figure 1c. Clear cell type RCC with no evidence of residual or recurrent RCC seen after RF ablation. (a) Nephrographic phase CT scan shows a solid mass in the right kidney. RF ablation was performed. (b) Excretory phase CT scan obtained 5 months after ablation shows a round mass with soft-tissue attenuation representing the ablated tumor. A curvilinear hyperattenuating area, or "halo" (arrowheads), is seen in the perinephric fat adjacent to the tumor. (c) On an excretory phase CT scan obtained 9 months after ablation, the mass is unenhanced, with fat replacement at the interface between the ablated tumor and the normal kidney (arrow) due to shrinkage of the tumor. Arrowheads indicate the curvilinear hyperattenuating area (cf b). Analysis of attenuation on both unenhanced CT scans and arterial phase and excretory phase CT scans showed no evidence of tumoral contrast enhancement.