Single 15-Min Protocol Yields the Same Cryoablation Size and Margin as the Conventional 10–8–10-Min Protocol: Results of Kidney and Liver Swine Experiment

Introduction: The objective was to determine the ablation size of a single 15-min freeze and compare it with the conventional 10-min freeze–8-min thaw–10-min freeze protocol. Secondary objectives were to determine the ablation margin and to ascertain whether islands of viable tissue remain within the ablation zone. Materials and Methods: Five adult swine under general anesthesia were used. After surgical abdominal exposure, two ablations were performed in liver and two in kidney. One ablation utilized the 15-min and the second the 10–8–10-min protocol. At maximum ice-ball, tissue ink was infused via an angiographic catheter in hepatic or renal artery to stain the non-frozen tissue. Animals were euthanized and organs examined macro- and microscopically. Results: Three histological regions were observed: (A) a viable/stained region representing the tissue outside the ice-ball, (B) a central necrotic area representing the ablated region within the ice-ball and (C) an unstained but viable margin representing the non-lethal margin within ice-ball. Ablation size did not vary with protocol but did for tissue type. Renal ablation was approximately 5 × 4 cm with both protocols, whereas liver ablation was approximately 6.7 × 4.4 cm. Ablation margin was measured at 1 mm irrespective of ablation protocol or tissue. No islands of viable tissue were identified within the ablation zone. Discussion: Fifteen-minute cryoablation yielded an ablation size and margin identical to that of the conventional 10–8–10-min protocol. Within the ablated region, cell death was uniform. The only difference was a larger cryoablation zone in hepatic tissue compared to renal tissue, likely attributable to differences in blood perfusion.