Relationship between the shape and size of radiofrequency induced thermal lesions and hepatic vascularization

Aims and background: The aim of this study was to evaluate the relationship between hepatic vascularisation and the final size and shape of radiofrequ ency (RF) induced thermal lesions. Methods: Series of four RF thermal lesions were created in explanted calf l ivers and in pig livers maintaining the following experimental conditions t hroughout the procedure: normal hepatic perfusion, occlusion of the hepatic artery, occlusion of the portal vein, occlusion of both hepatic artery and portal vein (Pringle maneuver) and subtotal occlusion of the hepatic veins . A 14G expandable needle electrode was used to make the thermal lesions. E ach lesion was created applying predetermined temperatures ranging between 95 and 115 degrees C and an exposure time of 20 minutes. Results: Occlusion of the hepatic artery during the RF procedure resulted i n moderate and not significant increases in thermal lesion diameter compare d with those obtained in normally perfused liver (3.0 +/- 0.4 cm vs 3.0 +/- 0.2 cm), while occlusion of the portal vein resulted in larger lesion diam eters (3.5 +/- 0.3 cm), In both these cases the diameters of the thermal le sions were smaller than those obtained in explanted calf liver (4.0 +/- 0.3 cm) and their shape showed peripheral irregularities. Thermal lesions larg er than those seen in normally perfused liver and equaling those observed i n explanted calf liver were created both during the Pringle maneuver (4.0 0.2 cm) and after subtotal occlusion of the hepatic veins (4.0 +/- 0.3 cm) , In both these cases the thermal lesions were regular in shape. Conclusions: Occlusion of the blood flow during the RF procedure avoids hea t loss by convection, resulting in the creation of larger thermal lesions t han those obtained in normally vascularized liver using the same electrode, temperatures and exposure time. This technique could therefore be employed in humans to destroy large hepatic tumor nodules.