Percutaneous ultrasound-guided radiofrequency ablation for kidney tumors in patients with surgical risk

Authors


Maciej Salagierski, md, ul. Żeromskiego 113, 90-549 Łódź, Poland. Email: msalagierski@yahoo.com

Abstract

Objective: The aim of this study was to describe our experience with percutaneous ultrasound-guided radiofrequency ablation of kidney tumors.

Methods: From July 2002 to August 2005, 45 radiofrequency ablations (RFA) in 42 selected patients with kidney tumor were performed. The patients had either contraindications to surgery procedures or had a solitary kidney. The average tumor size was 37.5 mm (range, 18–59 mm) with the mean age of 68 years (range, 28–83 years). RFA were performed based on radiographic findings. Needle biopsy was made only twice. Monopolar Cool-tip Tyco or bipolar Celon Olympus radiofrequency devices were used. The procedure was performed under conscious sedation with local anesthesia. Treatment efficacy was assessed by computed tomography and by Doppler ultrasound. The absence of contrast enhancement on computed tomography was considered to be a successful treatment.

Results: The average follow up was 14 months (range, 3–36 months). In 42 tumors (93%), total absence of contrast enhancement was obtained after the initial RFA and in three tumors (7%) after the second ablation session. There were no complications following 41 procedures, including all ablations in small (<35 mm) renal masses. In four procedures, minor complications were observed. All patients are alive. There has been no need for chronic hemodialysis and, until now, we have not observed any local recurrences with the exception of one metastasis to an ipsilateral adrenal gland.

Conclusions: RFA of kidney tumors is a promising alternative treatment which could be considered for patients who are not suitable for surgery.

Introduction

Renal cell cancer is the most frequent renal tumor and represents more than 90% of solid malignant masses detected in kidneys.1 Recently, due to the widespread use of imaging techniques it has become possible to detect very small and localized renal tumors at a very early clinical stage; for example, multi-detector computed tomography (CT) is capable of detecting lesions of approximately 5 mm.2 It has been shown that kidney tumors below 3 cm in diameter are generally not associated with metastasis and in the 10-year survival rate for these lesions the effect of nephron sparing surgery (NSS) is comparable to radical nephrectomy.3,4 Therefore, there is a rising need to search for minimally invasive therapies capable of destroying tumors without damaging renal function. Up to now, various forms of non-invasive kidney tumors treatment using different kinds of energy such as high-frequency focused ultrasound (HIFU), laser thermoablation, microwave therapy, cryoablation and radiofrequency ablation (RFA) have been introduced and developed.5,6 RFA employs the thermal effect of high-frequency current flow; when 300–500 kHz flows through tumoral tissue, the conduction of the radiofrequency current by the cellular fluid causes molecular friction and production of heat. This heat energy leads to tissue necrosis due to denaturation, desiccation and coagulation.7 RFA, which has so far had the most frequent application in coagulation of liver metastasis and inoperable lungs tumors,8,9 seems to be a successful method in treating kidney malignancies.10,11 It is a new kind of minimally invasive therapy used for treatment of relatively small (i.e. <3–4 cm), frequently exophytic tumors confined to an organ. RFA was performed in our department when there were contraindications to surgery or general anesthesia as well as in patients with a solitary kidney for whom NSS was critical in order to avoid renal replacement therapy. Our aim is to present our preliminary experience with a relevant number of patients who underwent RFA in kidney.

Methods

From July 2002 to August 2005, 45 RFA procedures in 42 selected patients with kidney tumor were performed. The average tumor size was 37. 5 mm (range, 18–59 mm) with the mean age of 68 years (range, 28–83 years). Four patients were over 80 years old. Most of the diagnosed kidney tumor candidates had contraindications to surgery, some of the patients with a solitary kidney did not accept nephrectomy and chronic hemodialysis. In our group, 14 patients had a solitary kidney, three had two tumors in one of the kidneys and one had cancer recurrence in the only kidney remaining after surgical NSS 6 years prior. Kidney tumors were localized out of the renal sinus, frequently in a lower pole near the exterior renal surface (Table 1). RFA was performed based on radiographic findings. In every case, the contrast enhancement of renal tumors of more than 20 Hounsfield units (HU) were described with CT. Needle biopsies were taken only twice when there was a suspicion of angiomyolipoma. Monopolar Cool-tip Tyco (Tyco-Valleylab, Boulder, CO, USA; 17-G, 20 cm in length with 20-mm active probe) or bipolar Celon Olympus (Medical and Industrial Equipment, Southend-on-Sea, Essex, UK; 18-G, 20 cm in length with 20-mm active probe) RFA devices under ultrasound (US) guidance (convex 3, 5 MHz) were used. Only two procedures were executed with bipolar RFA. RFA was performed under conscious sedation (i.v. fentanyl and midazolam) with local anesthesia (20 mL, 1% lidocaine along the needle tract). It consisted of one or two punctures of a single, straight RFA probe depending on tumor size. We made an US-guided puncture trying to obtain a 5–7-mm safe rim of normal renal parenchyma in order to avoid skip areas and to preserve oncological safety. For tumors less than 30 mm, one puncture of a RFA probe was enough to burn neoplastic tissue. For tumors over 30 mm, we placed two straight probes within 1 cm of each other before starting ablation. Afterwards, RFA by means of the first and then the second probe was performed. The ablation was stopped after reaching a temperature 70°C in the center of the tumor and the procedure was finished with tract ablation in order to prevent hemorrhage. The average RFA time was between 10 and 15 min, depending on the size of the tumor. It was considered to be enough to induce tissue necrosis.5,7 The coagulated tumor was left in situ and was not examined histopathologically. All patients received antibiotics for 5 days, and 60% of patients received a pain killer (paracetamol) the day of intervention as necessary. Treatment efficacy was assessed by a 16-detector CT in three-dimensional (3D) presentation and by Doppler US (to assess blood flow in preserved normal parenchyma) 3, 6, 12, 24 and 36 months following RFA. Absence of contrast enhancement on CT was considered to be a successful treatment (Figs 1–4). Renal function was evaluated with serum creatinine and urea levels.

Table 1.  Characterization of patients and tumors undergoing radiofrequency ablation (RFA)
No. patients42
No. tumors45
Repeated RFA 3
No. monopolar/bipolar43/2
Mean age (range)  68 (28–83)
Mean tumor size (range), mm37.5 (18–59)
Mean follow-up (range), months  14 (3–36)
Tumor location: exophytic/parenchymal39/6
Tumor location: lower/upper/mid-kidney pole21/16/8
Solitary kidney14
Synchronous kidney tumors 3
Angiomyolipoma 2
Complications (minor) 4
Complications (major)None
Figure 1.

Enhanced multi-detector computed tomography (MDCT) before radiofrequency ablation (RFA) procedure. Marked enhancement of solid renal tumor.

Figure 2.

Enhanced MDCT before RFA procedure. Marked enhancement of solid renal tumor.

Figure 3.

Enhanced MDCT after RFA procedure. Complete disappearance of tumor’s enhancement with good preservation of normal renal parenchyma.

Figure 4.

Enhanced MDCT after RFA procedure. Complete disappearance of tumor’s enhancement with good preservation of normal renal parenchyma.

Results

The average follow up was 14 months (range, 3–36 months; Table 1). Total absence of contrast enhancement was obtained after the initial RFA in 42 tumors (93%), and after the second ablation session in three tumors (7%). The RFA was repeated, in the three cases where incomplete tumor destruction was revealed on CT. Three patients had two small lesions in the same kidney and had RFA treatment for both tumors during the same procedure. There were no relevant complications following 41 procedures, including all RFA in small (<35 mm) exophytic renal masses. Three tumors which needed repetition of RFA were more than 34 mm (mean size, 47 mm). Tumors less than 34 mm showed no enhancement on CT after the initial RFA. In four interventions complications included: two patients had temporarily increased creatinine and urea levels in serum with fever up to 38.5°C; one patient had anuria, hyperkaliemia and uremia which demanded temporary hemodialysis; and one had neuralgia diagnosed later as shingles. There were no hemorrhage or bowel complications in any of the cases. All patients are currently alive. There has been no need for definitive renal replacement therapy in any of the cases with a solitary kidney and we have currently not observed any local recurrences, with the exception of one metastasis to an ipsilateral adrenal gland. The gland was removed, the kidney with the coagulated tumor was assessed during the procedure and its tissue was examined histopathologically; no vital cancer cells were detected.

Discussion

Thanks to the development of new technologies, renal tumor management has become less aggressive. New, minimally invasive treatment options make it possible to completely destroy cancer mass without affecting kidney function or damaging adjacent tissues. RFA can be executed percutaneously under US, CT and magnetic resonance imaging (MRI) guidance or intraoperatively (laparoscopically or by open surgical procedure). The intraoperative approach can be used if it is not possible to effectuate ablation percutaneously because of difficulties in reaching the lesion or because of large tumor size. For effective ablation, the temperature within the neoplastic mass should exceed 70°C.5,7 We stopped RFA procedures after reaching this temperature. Tract coagulation during percutaneous RFA is not done routinely. In the biggest recent study of a hundred renal tumors, tracts were cauterized when the risk of hemorrhage was elevated.12,13 We performed tract ablation in every case, not only to prevent hemorrhage but also to avoid cancer cell dissemination.

Percutaneous RFA seems to be a safe and efficient treatment option in small renal masses. Our results were also encouraging and coherent with data from other recent studies12–16 (Table 2). We had no major complication. We observed only one cancer progression (metastasis to an ipsilateral adrenal gland). Others authors12,13,17 reported rare complications after RFA procedures such as hemorrhage, ureteral injuries and uretero–pelvic junction obstruction, which were not observed in our group. Hospital stay and costs are often reduced because of a quick recovery. Our patients were discharged from hospital on the next day after the procedure. RFA can even be performed in outpatient clinics. Moreover, in case of incomplete tumor destruction (presence of contrast enhancement after initial RFA), it may be safely repeated (three patients in our group). Varkarakis et al. suggested that contrast enhancement after RFA may be due to inflammation or hemorrhage rather than presence of viable tumor.18 RFA could constitute an interesting therapeutic option for selected patients with contraindications to open surgery and for those who do not accept chronic hemodialysis. Being a non-invasive procedure, RFA provides a possibility of preserving renal function in patients with a solitary kidney, bilateral neoplastic disease, tumor recurrence in the contralateral kidney and in hereditary cancers with multiple kidney tumors in von Hippel–Lindau disease.19,20 There exists a possible application of RFA in metastatic renal cancer. This oncological entity is poorly responsive to radio and chemotherapy.21 For these patients, percutaneous RFA could constitute an important therapeutic option and could probably increase a survival rate.

Table 2.  Recent clinical series of percutaneous RFA of kidney tumors
AuthorsNo. of tumorsTumor size meanComplicationsComplete ablation
Gervais et al. 20051003.2 cmHemorrhage (two major, three minor, one inflammatory), track mass, two transient lumbar plexus pain, two ureteral injuries, one skin burns 
<3 cm100%
3–5 cm92%
>5 cm25%
Veltri et al. 2004 182.6 cmPain, minimal hemorrhage 83%
Ukimura et al. 2004  93.8 cmOne temporary hematuria, one perirenal hemorrhage 78%
Su et al. 2003 352.2 cmOne burn injury to the liver, one died (history of severe pulmonary compromise), eight hematomas 94%

Ultrasound guidance is sufficient for precise needle placement in RFA, but unfortunately it is difficult to follow the developing thermal lesion because of tissue vaporization which restricts visibility. That is why in bigger tumors, to have a better control of RFA and to obtain the overlapping effect, we placed two probes into the tumor mass before starting the procedure. (It is thought that a single probe causes spherical necrosis in approximately 0.8–1.6 cm in diameter and the overlapping effect is seen when the probes are within 1.5 cm of each other7,22). At present, the only imaging modality to observe the lesion in real-time remains MRI; RFA causes a predictable loss of T1 signal.19 However, the access to perform RFA under MRI guidance remains limited. Particularly difficult to ablate are tumors more than 5 cm which are situated close to the renal sinus.23 There are serious doubts regarding its efficiency, which concerns its oncological safety. It is critical to achieve the satisfactory margins around the cancer mass. It is thought that the safe margins are 5 mm beyond the tumor.5 Without perfect devices to follow the ablation process, it is difficult to obtain precise margins. There is no perfect tool for detecting local renal recurrences. The absence of contrast enhancement on CT does not exclude the presence of viable cancer cells. The first RFA of renal tumor was described by Zlotta et al. and was made prior to nephrectomy.24 Histopathology did not show presence of cancer cells in the ablated tumor. On the other hand, Michaels and Rendon performed nephrectomy following RFA and showed absence of total tumor necrosis and presence of neoplastic cells after ablation procedure.25,26 The efficacy of different therapeutic approaches in kidney cancer management has been recently compared in animal studies. There was no significant difference between the results of RFA, cryoablation and nephrectomy in small rabbit kidney tumors of less than 1 cm. All these treatment modalities were efficient.27 Moreover, there was no impact of RFA on renal function and blood pressure after ablation of small tumors.28 Another study compared monopolar and bipolar RFA in porcine kidney tumors. Bipolar RFA seemed to be more effective and caused larger destruction than monopolar RFA.29 In our study, we had too little experience to compare both techniques. Only two RFA were performed using a bipolar system (Table 1).

Conclusions

Radiofrequency ablation gives a chance for patients who are not suitable for surgery to recover from kidney malignancies. Complications are not frequent. Procedure is well tolerated, safe and can be successfully repeated in case of incomplete tumor destruction. Furthermore, hospitalization time is very short compared to traditional interventions. It is a good treatment modality which could be proposed to select patients, especially older ones with small renal masses of less than 4 cm. Another interesting application of RFA concerns thermal destruction of benign renal tumors such as angiomyolipoma. However, the long-term oncological efficacy of RFA should still be established.

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