Ablation of liver tissue: a comparison between microwave, cryotherapy and radiofrequency

Introduction The majority of primary and secondary liver tumours are inoperable. „In situ‟ thermal destruction techniques such as radiofrequency, microwave ablation and cryotherapy have been employed to treat these inoperable tumours. Despite recent advances in these technologies, large and peri-vascular tumours still suffer from a relatively high recurrence rate post ablation. This is thought to be due to the loss of thermal energy to surrounding vasculature, known as the heat sink effect. The aim of this project was to investigate the effect of surrounding vasculature on ablation morphology and success and compare the three most popular ablation modalities. Methods Standard sized ablations were created in rat liver at various distances from the hilum with all three methods. At various time points, tissue samples were retrieved and underwent histological (H&E) and immuno-cytochemical (Hsp70 and Caspase 3) staining in order to assess lesion evolution and the effects of surrounding vasculature on ablation completeness. Results All rats survived. The greatest amount of activity was seen in the transition zone. H&E and immuno-cytochemical analyses of lesion evolution discovered previously unreported cellular changes, particularly in the transition zone. Cryotherapy ablation seemed to be the most irregular and unpredictable of the three. Radiofrequency ablation was uniform but showed evidence of extra-lesional apoptosis and perivascular cell survival in addition to Hsp 70 activity in the transition zone that was affected by surrounding vasculature. Microwave ablation seemed to be influenced least by surrounding vasculature and formed the most uniform lesion with very little extra-lesional collateral damage. Conclusion The success of ablation is dependent upon the adjacent blood vessels and microwave ablation seemed to form the most predictable burn and be least affected by surrounding vasculature compared to radiofrequency. Cryotherapy should not be used as first line treatment to treat unresectable liver tumours. In addition the exact role of HSP 70 on the fate of cells in the transition zone, and the subsequent final ablation size and morphology is yet to be determined. Larger ablations in larger animal models may help answer some of these questions.