Renal cryosurgery: experimental evaluation of treatment parameters

Cryosurgery represents a minimally invasive alternative for the management of small or equivocal lesions of the kidney. We evaluated the relationship between ultrasonographic appearance and intrarenal temperatures and the effect of renal artery occlusion on the efficacy of the freezing process in a canine model.

Ten animals were treated with intraparenchymal cryoablative therapy with (n = 5) or without (n = 5) renal artery occlusion using a rapid freeze technique. Intrarenal temperatures were measured 1.0 cm away from the cryoprobe at various times during the freezing process. The distance from the cryoprobe to the ice ball as monitored by ultrasonography was also determined. The contralateral kidney was removed to facilitate studies of renal function and all animals were killed on day 28 for autopsy and histopathologic examination.

A target temperature of less than -20 degrees C was achieved 3.1 mm behind the ice ball in all animals tested. The ice ball stabilized at a radius of 16 mm with prolonged treatment, suggesting that multiple probes will be required to treat renal lesions greater than 2.5 cm in diameter. Renal artery occlusion did not significantly alter the freezing process and provided no practical advantage. Renal function remained stable (final serum creatinine level 1.5 mg/dL or less) in all but 1 animal in which an obstructive stricture of the ureteropelvic junction developed. Effective tissue ablation was confirmed at the treatment site in all instances.

Renal cryoablative therapy is a nephron-sparing modality that can be delivered in a safe, efficacious, and reproducible manner. The treatment parameters defined in this study should allow for intelligent patient selection and rational administration of renal cryotherapy.