The effects of intentional cryoablation and radio frequency ablation of renal tissue involving the collecting system in a porcine model.
PURPOSE: Ablative techniques for the treatment of urological malignancy are gaining acceptance and they are likely to become more widely used in clinical practice. Indications and limitations of the technologies are still evolving. In a porcine model we evaluated the safety and efficacy of cryotherapy and radio frequency ablation (RFA) of cortical and deep renal tissue. MATERIALS AND METHODS: In 11 swine argon gas based cryoablation or RFA of renal tissue adjacent to the collecting system was performed using a laparoscopic or percutaneous approach. Lesions created in renal units 30 days or 2 hours prior to harvest were termed chronic or acute. Using single or multiple 17 gauge cryoneedles or 3.0 mm cryoprobes and 2 freeze-thaw cycles (10-minute freeze and 5-minute thaw) 13 acute and 10 chronic cryolesions were made. Using a single 16 gauge umbrella-shaped RFA probe and 2 heating cycles to maximum impedance 13 acute and 4 chronic RFA lesions were made. Gross and microscopic tissue analysis was performed to assess lesion size and renal parenchymal, collecting system and arterial effects. Acute cryolesion size estimation by laparoscopic or transcutaneous ultrasound (US) was compared with pathological lesion size. RESULTS: Acute cryolesions on hematoxylin and eosin staining demonstrated uniform coagulative necrosis of renal parenchyma and chronic cryolesions demonstrated uniform necrosis with fibrous scar formation. Interlobar artery (adjacent to renal pyramid) preservation occurred in 7 of 13 acute and 5 of 9 chronic cryolesions. Urothelial architecture was preserved in 8 of 13 acute and 7 of 9 chronic cryolesions. Acute and chronic RFA lesions demonstrated indeterminate necrosis on hematoxylin and eosin staining, although triphenyl tetrazolium chloride staining of gross specimens confirmed necrosis most definitively in renal cortex. Interlobar artery preservation occurred in 6 of 13 acute and 3 of 4 chronic RFA lesions. Urothelial architecture was preserved in 1 of 13 acute and 2 of 4 chronic RFA lesions. Acute cryolesion dimensions measured by laparoscopic US equaled or underestimated lesion size measured grossly in all 6 cases. Lesion dimensions measured by transcutaneous US equaled or underestimated true lesion size in 3 of 6 cases. In 3 of 6 lesions transcutaneous US overestimated true lesion size by 20%, 76% and 260%, respectively. CONCLUSIONS: Renal cortical tissue can be effectively destroyed by cryoablation or RFA. However, treatment of deep parenchymal lesions with either modality may result in incomplete ablation. Cryosurgery but not RFA spares the collecting system in an acute setting. However, healing or regrowth of the urothelium may occur with time after RFA. Laparoscopic US is more accurate for cryolesion monitoring than transcutaneous US.