Effects of Perfusion on Radiofrequency Ablation in Swine Kidneys

Abstract

PURPOSE:To evaluate the effect of vascular occlusion on the size of radiofrequency (RF) ablation lesions and to evaluate embolization as an occlusion method. MATERIALS AND METHODS:The kidneys of six swine were surgically exposed. Fifteen RF ablation lesions were created in nine kidneys by using a 2-cm-tip single-needle ablation probe in varying conditions: Seven lesions were created with normal blood flow and eight were created with blood flow obstructed by means of vascular clamping (n = 5) or renal artery embolization (n = 3). The temperature, applied voltage, current, and impedance were recorded during RF ablation. Tissuecooling curves acquired for 2 minutes immediately after the ablation were compared by using regression analysis. Lesions were bisected, and their maximum diameters were measured and compared by using analysis of variance. RESULTS:The mean diameter of ablation lesions created when blood flow was obstructed was 60% greater than that of lesions created when blood flow was normal (1.38 cm ± 0.05 [standard error of mean] vs 0.86 cm ± 0.07, P < .001). The two methods of flow obstruction yielded lesions of similar mean sizes: 1.40 cm ± 0.06 with vascular clamping and 1.33 cm ± 0.07 with embolization. The temperature at the probe tip when lesions were ablated with normal blood flow decreased more rapidly than did the temperature when lesions were ablated after flow obstruction (P < .001), but no significant differences in tissue-cooling curves between the two flow obstruction methods were observed. CONCLUSION:Obstruction of renal blood flow before and during RF ablation resulted in larger thermal lesions with potentially less variation in size compared with the lesions created with normal nonobstructed blood flow. Selective arterial embolization of the kidney vessels may be a useful adjunct to RF ablation of kidney tumors. Radiofrequency (RF) ablation is a relatively new minimally invasive image-guided tumor treatment. Although RF ablation has been used principally for the treatment of nonresectable liver tumors, in selected clinical settings it may represent an alternative to parenchyma-sparing surgery for the treatment of small renal malignancies with diameters of less than or equal to 3 cm (13-17).The combination of selective renal artery embolization and RF ablation may increase the volume of the thermal lesion and thus could be useful in the treatment of tumors larger than 3 cm in diameter. Selective embolization results in decreased blood flow, which leads to a reduced amount of convective cooling and thus an increased extent of tissue heating. By performing selective arterial embolization, one may also decrease the possibility of hemorrhagic complications after RF ablation, which may be a greater risk with larger tumors.We are aware of only one study of the effect of transcatheter vascular occlusion on RF ablation lesion size in the kidney. In that study, which was performed by Aschoff et al (18), the temporary balloon obstruction of renal blood flow in swine resulted in larger RF abl...

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