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

The aim of this study was to evaluate the relationship between hepatic vascularisation and the final size and shape of radiofrequency (RF) induced thermal lesions.

Series of four RF thermal lesions were created in explanted calf livers and in pig livers maintaining the following experimental conditions throughout 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. Each lesion was created applying predetermined temperatures ranging between 95 and 115 degrees C and an exposure time of 20 minutes.

Occlusion of the hepatic artery during the RF procedure resulted in moderate and not significant increases in thermal lesion diameter compared 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 diameters (3.5 +/- 0.3 cm). In both these cases the diameters of the thermal lesions were smaller than those obtained in explanted calf liver (4.0 +/- 0.3 cm) and their shape showed peripheral irregularities. Thermal lesions larger than those seen in normally perfused liver and equaling those observed in 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.

Occlusion of the blood flow during the RF procedure avoids heat loss by convection, resulting in the creation of larger thermal lesions than 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.