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Minimally Invasive Treatments in Renal Cell Carcinoma

Cryoablation is the most studied and clinically used modality for ablation of kidney tissue. The cryoprobes are placed directly into the tumor; circulating liquid nitrogen (–196°C) or argon gas (–186°C) rapidly freeze the tissue which causes crystal formation in the microvasculature, extracellular spaces and within the cells. Progressive failure of the microvasculature results in endothelial cell damage, edema and platelet aggregation with thrombosis and vascular occlusion. Thirteen weeks following ablation, fibrous collagen bundles replace the region of coagulation necrosis (6). Although elements of tissue destruction are achieved with both the freeze and the thaw process, continued investigation remains to be performed to determine the optimal cycle of therapy (number of freezes, length of freezes, type of thaw: active/passive; (7, 8)). Renal artery occlusion does not significantly alter the freezing process and provided no significant advantage in an animal model (9). Threshold temperature for achieving reliable cell death of normal and cancerous renal cells is near –20°C (10). The margin of cell death beyond the probe is an important consideration in deciding the depth of probe deployment. To achieve the tumoricidal –20°C temperature within the entire extent of the tumor, the ice ball has to be extended about 1 cm beyond the border area of the tumor (11). The developing ice edge must be constantly monitored during freezing due to the destructive nature of the ice ball and the inability to rapidly arrest its progression. During open or laparoscopic application, real-time ultrasound is the most common monitoring modality. The evolving renal ice ball is visualized as a hyperechogenic, crescendic advancing edge with posterior acoustic shadowing. The ultraREVIEW Scandinavian Journal of Surgery 93: 137–144, 2004