Efficiency Analysis of Bipolar and Multipolar Radiofrequency Ablation in an In Vivo Porcine Kidney Model Using Three-Dimensional Reconstruction of Histologic Section Series

Background and Purpose: Radiofrequency ablation (RFA) was established for minimally invasive treatment of small kidney tumors in multimorbid patients. Bipolar and multipolar RFA may allow the treatment of larger tumors. Safe tumor coagulation depends on total energy supplied and proper electrode placing. To investigate the influence of energy on ablation size and shape in intact kidneys, we used cooled bipolar and multipolar RFA in an in vivo pig model. Materials and Methods: Twenty-five male pigs were treated with percutaneous bipolar (one electrode) or multipolar (two electrodes) RFA with various energy transfer under laparoscopic visual control. The animals were sacrificed 4 to 5 hours after RFA. Volume and shape of the coagulation zone was analyzed by three-dimensional reconstruction of hematoxylin and eosin and diaminobenzidine stained paraffin serial sections. Heat-induced cellular activation was addressed by immunohistologic detection of apoptosis marker proteins heat shock protein 70 (Hsp70) and caspase-3 (Casp3). Results: Multipolar RFA led to significant larger tissue ablation than bipolar RFA. Increasing energy, however, did not result in significant enlargement of the coagulation volume. Shape control was better in bipolar RFA. Hsp70 and activated Casp3 immunoreactivity were increased close to the central coagulation zone and occasionally in the caliceal system. Conclusions: RFA causes minimal tissue damage beyond the primary coagulation zone, indicating that RFA is a safe, minimally invasive method for treatment of renal tumors. The ablation of larger volumes necessitates further improvement of multipolar RFA. These findings may be of general interest, because treatment failure correlates with mass size in monopolar RFA and cryoablative techniques as well.