Histologic differences between cryothermic and hyperthermic therapies

Minimally invasive cryothermic and hyperthermic therapies are being increasingly used to destroy dysfunctional and neoplastic tissues in several organ systems. This report morphologically compares the acute tissue responses that follow cryothermic and microwave therapy in porcine kidneys. Three cryothermic and hyperthermic groups of treated kidneys were pooled from other studies for evaluation (six groups; six kidneys/group): 1) in vitro treated non-perfused, 2) in situ treated with 2-hour post in vivo perfusion, and 3) in situ treated with 3-day (cryothermic) or 7-day (hyperthermic) post in vivo perfusion. The cryolesions showed uniform central coagulative-type necrosis and interstitial hemorrhage. The hyperthermic lesions showed central thermal fixation and a rim of coagulative necrosis. The cryothermic and hyperthermic lesions both had a similar narrow transition zone of partial cell injury. The cryothermic lesions developed a wound healing response that advanced into the central lesion. In contrast, the heat-treated tissues lacked a prominent wound healing response and appeared to resist breakdown/repair by the body. Thus, the tissue effects of and responses to cryothermic and heat injury appear to be different.