Dynamic intrahepatic flow and cellular alterations during radiofrequency ablation of liver tissue in mice

PURPOSE: The purpose of this study was to identify microvascular and other associated changes that occur in the liver during focal heating with monopo lar radiofrequency (RF). MATERIALS AND METHODS: Intravital video microscopy was performed on exterio rized transilluminated livers of 15 live mice during RF-induced heating of liver parenchyma. Microvascular flow parameters, flow reversibility, microb ubble formation, phagocytic activity, and endothelial permeability were rec orded throughout a range of tip temperatures (40 degreesC-95 degreesC). RESULTS: During RF application, five discrete zones extended outward from t he electrode surface: (i) tissue coagulation, (ii) cellular edema/necrosis, (iii) sinusoidal stasis, (iv) parenchymal shunting, and (v) normal liver t issue. Reversal of stasis in sinusoids and small (< 25 mum) vessels occurre d at tip temperatures below 50 degreesC. This zone of stasis corresponded t o the hyperemic zone on histologic analysis. Although alterations in permea bility and phagocytic activity were first identified at 43 degreesC, tip te mperatures higher than 55 degreesC always produced local endothelial leakin ess to carbon microparticles at the periphery and always inhibited phagocyt ic activity. At tip temperatures higher than 95 degreesC, microbubble forma tion occurred with bubbles ultimately tracking through necrotic tissue into patent sinusoids. Larger peripheral vessels (> 30 mum) limited extension o f coagulation. CONCLUSION: Although coagulation occurs at tip temperatures higher than 50 degreesC, RF heating induced reversible microvascular stasis at temperature s lower than 50'C. Increased sinusoidal endothelial permeability occurs at near-coagulative temperatures. Therefore, targeted endovascular micropartic le delivery through this leaky endothelium may provide an additional and co mplimentary adjunct for RF ablation therapy.