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.