Precise characterization of renal parenchymal response to single and multiple cryoablation probes.

PURPOSE: We characterized the size and shape of the ablated area, and the surrounding indeterminate zone associated with renal cryolesions produced by single and multiple cryoablation probe configurations in a porcine model.
MATERIALS AND METHODS: Laparoscopic cryoablation, consisting of 2, 10-minute double freeze cycles followed by a 3-minute active thaw, was performed in 18 pigs. Three groups of 6 pigs each were studied, including a single IceRod, 3 rods arranged in a triangular configuration 2 cm apart from each other and 4 rods arranged in a quadratic configuration 2 cm from each other. Cryoablated kidneys were harvested after 14 days for histopathological evaluation.
RESULTS: The mean diameter of the area of complete ablation produced by a 1, 3 and 4 rod configuration 1 cm from the tip of the rod was 2.0, 4.4 and 4.9 cm, respectively. Cryolesions were elliptical with 1 cryoablation probe and in the 3 and 4 rod configurations they conformed to triangular and quadratic cross-sectional shapes, respectively. In the zone, ablation a single small focus of peri-arteriolar renal cell viability was noted less than 1 mm from the edge of the cryolesion in 1 of the 18 cryolesions. Otherwise no viable renal cells were detected.
CONCLUSIONS: Multirod configurations can be used with templates to space cryoablation probes 2 cm apart from each other with reliable and complete ablation overlap between the rods. However, around larger blood vessels the ice ball must be extended to a larger margin to ensure complete tissue ablation.