Effect of vessel size on creation of hepatic radiofrequency lesions in Pigs: Assessment of the "heat sink" effect

OBJECTIVE. The effect of vessels and their size on radiofrequency lesion creation in the liver was evaluated with respect to potential for vascular injury and perfusion-mediated "heat sink" effect. SUBJECTS AND METHODS. Radiofrequency lesions targeted to tissue adjacent to a variety of vessels were created in vivo in the liver of 10 Yorkshire pigs. Postablation contrast-enhanced CT and then histopathologic analysis of the vessels and lesions were performed after sacrifice of the pigs. Degree of vascular injury and viability of perivascular hepatocytes were recorded and tabulated according to vessel size for both CT and histologic data sets. RESULTS. At CT, 42 (95%) of 44 veins greater than 3 mm remained patent, and four (20%) of 20 veins less than 3 mm were occluded. Heat sink effect, indicated by invagination of enhancing tissue between vessel and radiofrequency lesion, was observed in 32 (73%) of 44 veins greater than 3 mm. and in zero of 20 veins less than 3 turn. On histopathology, 111 (100%) of 111 vessels less than 3 rum showed at least partial vessel wall injury, characterized by endothelial cell necrosis and luminal thrombus. In 24 vessels greater than 3 mm, the extent of vessel wall injury decreased with increasing vessel diameter. Viable perivascular tissue indicative of heat sink effect was identified in 12 of 24 veins greater than 3 mm, increasing to seven of seven veins greater than 5 mm. None of 96 vessels less than 2 nun and three of 111 vessels less than 3 mm showed any heat sink effect. CONCLUSION. There appears to be a-narrow transition zone for hepatic vessels at 2-4 nun, beyond which the heat sink effect was seen consistently and substantial vascular injury was rare.