Discussion

Recently, the indications for RF ablation of malignancy have been rapidly enlarged because of its feasibility and utility. Several studies have reported the treatment of renal malignancies by RF ablation [8-11,17-19].According to those papers, the complete ablation rate is as high as 79% to 100% [17-19]. Complete ablation was reported even in an exophytic RCC 5 cm in diameter [19]. On the other hand, in RCCs of parenchymal localization adjacent to the renal sinus, complete ablation was sometimes difficult if the tumor diameter was smaller than 3 cm [19]. Our results showed the same tendency. Our success rate was 94%, although one parenchymal tumor could not be completely ablated, despite repeated ablations. Near the renal sinus, the central portion of the kidney contains large vessels that serve as a heat sink because of the constant inflow of blood at body temperature. However, when we ablate an exophytic tumor, the temperature conditions are different. With respect to tissue characteristics, the kidney is surrounded by fat that serves as a heat insulator. Higher ablation temperatures can be achieved and maintained in tumors that are surrounded at least in part by fat. As a result, exophytic tumors seem to be more easily treatable. Gervais et al. reported that when one is assessing a tumor for possible ablation, one can select exophytic tumors up to 5 cm in size with a high certainty that the procedure will be successful [19]. On the other hand, among tumors larger than 3 cm, those with a central component near large vessels were less likely to be treated with technical success than those without such a component. Thus, tumor location seems to be the most important factor for successful ablation of malignant renal tumors. However, even if a tumor is exophytic but located near the bowel, we must pay attention to prevent bowel perforation by burning.

We planned RF ablation with axial images from preoperative CT scans. RF ablation was then performed under CT fluoroscopic guidance. Overlapping ablations were performed by repositioning the needle to ablate the entire tumor, and we usually repositioned a needle less than 1 cm from the track of the needle positioned immediately before. By careful ablation under CT fluoroscopic guidance, we could obtain good results. However, we once performed an incomplete ablation of the caudal part of the tumor in the first ablation in one tumor. This was probably due to the underestimation of the caudal extension of the tumor by interpretation of only axial CT scan images. Sagittal, and coronal preoperative reconstruction images will reduce this kind of mistake.

We had two patients with VHL. Such patients often present with RCC at a young age and develop multiple and bilateral RCC tumors that result in multiple resections, total nephrectomy, and finally the need for dialysis [17,18,22]. RF ablation enables maximal maintenance of residual renal function and delays the start of dialysis. RF ablation may become the first choice for treatment of RCC in patients with VHL. Like patients with VHL, patients with a solitary kidney can obtain great benefit by RF ablation treatment when they suffer from RCC. They also need maximal maintenance of residual renal function after treatment.

Reported complications of percutaneous RF ablation include nausea, pain, hematuria, and hematoma [17,19]. Although a case of ureteral stenosis causing renal dysfunction after RF ablation was reported [19], no other severe complications have been reported in the previous studies. There were no severe complications among the patients in our study. Among five patients in our series with a solitary kidney, no renal dysfunction was observed after RF ablation. RF ablation is a safe and feasible treatment for RCC.

Percutaneous RF ablation should be compared with partial nephrectomy, i.e., nephron-sparing surgery. Uzoo et al. [20] described the complication rates and outcomes of nephron-sparing surgical procedures in a review of reports of these procedures. The survival data for nephron-sparing surgical procedures are similar to those for radical nephrectomy. The rate of major complications ranged from 4% to 30% in nine series, with a cumulative total of 155 (13.7%) complications in 1129 procedures. The reported results of RF ablation, including our study, are favorable compared with the results of partial nephrectomy.

In conclusion, RF ablation for RCC is a minimally invasive and effective treatment. It will be able to replace partial nephrectomy for the treatment of RCC in patients who are at high risk during anesthesia and surgery, those with a solitary kidney, and those with VHL.

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