Kidney Radiofrequency Ablation for Small Renal Tumors: Oncologic Efficacy

Abstract

Background and Purpose:

The introduction of radiofrequency ablation (RFA) into other fields of surgery has fueled the interest to study its application in small renal masses (SRM). Some controversies remain, however, regarding its oncologic efficacy. We review technical factors and tissue characteristics that influence treatment success, discuss the evaluation of treatment success by post-treatment imaging and histopathology, and highlight intermediate-term oncologic outcomes of recent, larger RFA series.

Materials and Methods:

A search of the MEDLINE database regarding the treatment of SRM by RFA was performed from 2003 through August 2009. For the purpose of describing technical factors and tissue characteristics that influence treatment success and the evaluation of treatment success by imaging and histopathology, articles were selected when they provided detailed descriptions of one or more of these items. For the analysis of oncologic outcomes, the selection was limited to series in which a minimum of 20 patients were treated and that provided effectiveness based on follow-up imaging.

Results:

Technical evolutions and correct patient/tumor selection have led to increasingly higher success rates being achieved by RFA. Even though tumor skipping has been described in preclinical studies and early clinical studies, this does not seem to influence final success. Indeed, a 8.6% re-treatment rate has to be taken into account. Accepting this, the final ablative success rate is 93.8% at intermediate-term follow-up. Complications after RFA are less frequent and more often minor compared with surgical series.

Conclusions:

The present analysis reveals that RFA achieves a high intermediate-term ablative success rate when accepting a 8.6% reablation rate. Complication rates are low and mostly minor. Those facts render RFA an attractive minimally invasive treatment for SRM, especially in the growing elderly patient population with multiple comorbidities. Long-term follow-up data are expected to confirm the role of RFA in the management of SRM.

Introduction

T he increased use of modern imaging techniques has led to a marked diagnostic increase of asymptomatic small renal masses (SRM) with no evidence of metastatic disease. The greatest incidence of these tumors occurs in patients who are older than 70 years in whom multiple comorbidities may increase the risks of surgery.¹ SRMs have been characterized by slow growth and metastatic potential that mostly arises beyond 3 cm. Aggressive characteristics, however, have been described in more than one third of SRMs; therefore, the true natural history remains largely unpredictable.²

Radical nephrectomy (RN) has been abandoned as the gold standard treatment for SRMs. Nephron-sparing surgery (NSS) has taken over, providing equal cancer control and improved renal function preservation.³

These facts have helped minimally invasive thermoablative therapies (MITT) make their entrance into the field of urology. MITTs may theoretically avoid the invasiveness of surgical extirpation and at the same time avoid warm ischemia time with secondary loss of nephrons. Furthermore, the fear of leaving a potentially life-threatening renal-cell carcinoma (RCC) untreated when opting for active surveillance could theoretically be countered using MITT.⁴

The introduction of radiofrequency ablation (RFA) into other fields of surgery has fueled the interest of the urologic community to study its application in SRMs. RFA is arguably the least invasive treatment because it is easily applicable through the percutaneous approach.

Some controversies remain, however, regarding its oncologic efficacy. Areas of viable tumor tissue within the ablation zone have been described (tumor skipping). Re-treatment rates of up to 30% have been published.⁴ While intermediate-term results seem to be promising when accepting the need for reablation for residual tumor, long-term oncologic outcomes are still awaited.

We aim to review the technical factors and tissue characteristics that influence treatment success, discuss the evaluation of treatment success by post-treatment imaging and histopathology, and highlight intermediate-term oncologic outcomes of recent, larger RFA series. This review may help to clarify some of the remaining controversies. It also provides a focused view on all aspects that determine the oncologic outcome of this novel and promising MITT.

Materials and Methods

Data sources

A search of the MEDLINE database was performed from 2003 through August 2009 to review the world literature regarding the treatment of renal masses by RFA. The PubMed database was searched using the following “free text” combinations: “Minimally invasive technique AND renal tumor” that generated 162 articles and “radiofrequency AND renal tumor” with 440 articles retrieved. Further free text searches were performed by separately adding to the combination radiofrequency and renal tumor the following key words: “technique,” “imaging,” “recurrence,” and “survival.” Abstracts reported in journal supplements were excluded.

Study selection and data analysis

Published articles were selected when they provided detailed descriptions of technical factors and tissue characteristics that influenced treatment success, and the evaluation of treatment success by post-treatment imaging and histopathology. For the analysis of oncologic outcomes, the selection was limited to series with a minimum of 20 patients or 35 tumors that were treated by RFA and that based effectiveness on follow-up imaging. Studies that provided results from the same center were screened and the most appropriate (highest case numbers, longest follow-up) were included in the analysis. This selection was applied to exclude series with a limited number of tumors treated representing the early learning curve of a center starting RFA treatment of SRM, thus selecting more representative studies to allow a better assessment of the effectiveness of the technique.

We did not limit the selection to series that only included pre-RFA renal biopsies, because many series do not provide this in detail. The percentage of biopsy-proven RCC was collected for each separate study, however. Post-treatment biopsies were not an exhaustive factor in the selection of appropriate studies, because this factor is very infrequently used as a determiner of success in the available literature.

The number and mean age of patients, number and mean diameter of tumors, mean follow-up duration, success and final success ratio were extracted or calculated from the published series. For all these variables, we determined the weighted mean (weighted for study size). Successful treatment was defined as the absence or decrease in contrast captation on follow-up CT or MRI after one session. The final success ratio comprises the percentage of patients who do not show contrast captation on imaging after one or more sessions.

Results

Technical factors and tissue characteristics that influence treatment success

The goal of RFA is to destroy tissue by heat. During the procedure, a needle is placed within the tumor, and alternating current is sent through the needle. The ions in the tissue that surround the uninsulated needle tip attempt to follow this alternation and become agitated. As a result, frictional heating occurs within the tissue. Thus, it is the tissue itself and not the needle that delivers the heat for destruction.⁵

Starting at temperatures of 42°C, tissues are affected by thermal injury.⁶ At temperatures of 60°C, immediate cell death occurs through protein denaturation.⁷ In addition to the direct cytotoxic effect of heat, vascular damage occurs because of microvascular cell swelling and disruption, intravascular thrombosis, and neutrophil adherence to venular endothelium. This results in a decrease in microvascular perfusion during RFA and vascular shutdown after RFA. After the initial treatment, progression of marginal vessel injury may lead to additional tissue necrosis.⁵

With temperatures that are higher than 105°C, cellular fluids start to boil and produce gas bubbles. Even higher temperatures cause tissue charring. Both these phenomena cause a rise in impedance that prevents the alternating current to reach tissue beyond the char or gas bubbles. This has a direct influence on the size of the ablation zone.⁵

In pursuit of treating larger lesions more effectively, RFA has evolved tremendously since the first ablations. The technique underwent an evolution toward the use of high-power generators, impedance based generators, thinner electrodes, saline-perfused electrodes, and internally cooled electrodes, resulting in larger ablation zones and more effective ablations.^8

–11 The discussion of different needles and generators is not within the scope of this review.

Ablative success depends not only on the technical aspects of energy delivery, but also on tissue factors.¹² Ahmed and associates¹³ showed that lesion size and maximal temperature reached during RFA are significantly influenced by the conductivity and blood flow of surrounding tissue. They described a “heat sink” phenomenon in kidney RFA: Smaller lesion diameters and lower temperatures were achieved when blood flow was present in the vicinity of the tumour. Similarly, Gervais and colleagues¹⁴ suggested that the overlying fat on exophytic tumors has an insulating effect, resulting in higher ablation temperatures and success, in contrast to the endophytic lesions that are adjacent to the renal sinus, where the renal vessels might act as a heat sink. Klingler and coworkers¹⁵ also noticed that highly vascularised tumors had a higher risk for failure.

Approach and image guidance

Approach

RFA for kidney lesions is performed both by a percutaneous and laparoscopic approach. The laparoscopic approach has the advantage of direct visualization of the tumor and needle positioning, resulting in higher success rates after first treatment. Complication rates, however, are higher in laparoscopically treated patients. A percutaneous approach allows for easier reablation than a laparoscopic approach, resulting in comparable final success rates after sometimes multiple ablations.¹⁶ Therefore, the percutaneous approach is still favored.

One of the possible advantages of percutaneous RFA is the feasibility of treating kidney tumors with patients under local anesthesia with conscious sedation, making it a true minimally invasive technique that is suited for frail patients with comorbidities. RFA in patients who are under general anesthesia, however, generates better results than in those under local anesthesia, probably because of absent patient movement and better controlled breathing, which allows for more accurate needle placement.¹⁷

Image guidance

This can be performed by ultrasonography (US), CT, or MRI. Because of blurring of the US image when gas bubbles appear during RFA, this imaging modality seems to be least favored.¹⁸ Contrast-enhanced CT guidance is a valid option, because it improves real-time tumor margin identification and targeting.¹⁷ Contrast administration is necessary, however, which might preferably be avoided in patients with renal insufficiency or contrast allergy. In addition, contrast administration can only be performed once per procedure, because the contrast clearance may need several hours. It follows that residual tumor cannot be detected immediately, limiting the possibility of targeted repeated ablation cycles in the same session.

Theoretically, the most suited image guidance at this time is MRI. It provides near real-time monitoring of the ablation procedure, and residual tumor tissue can be detected during the treatment because of its persisting isointense or hyperintense signal.¹⁸ Unfortunately, not all RFA equipment is designed to be used in the MRI magnetic field, and for practical reasons, an “open” MRI scan is needed, both limiting the use of MRI-guided RFA.

Pretreatment renal mass biopsy

The most recent literature shows that biopsy of renal masses can provide an accurate differentiation between malignant and benign tissue in >90% of the cases. The rate of inconclusive biopsies ranges from 3% to around 20%. Significant bleeding is a rare event, and tumor seeding has an estimated risk of <0.01%. Fine-needle aspiration cytology is not diagnostic in 12% to 19% of cases according to recent literature, and it may be advisable to use fine-needle biopsy.¹⁹

In conclusion, renal mass biopsy before RFA is an essential prerequisite to interpret the oncologic outcome of the procedure.

Post-treatment histopathology

Microscopically, cell death mediated by RFA cannot be compared to commonly occurring cell death. The high temperatures in the ablation zone cause immediate tissue coagulation. The cellular structure and content undergo an instantaneous heat fixation effect.²⁰ Staining of the ablated tumor with hematoxylin and eosin (H&E) shows typical histopathologic findings such as loss of pycnotic nuclei, cytoplasmic vacuolization and dissolution, nuclear elongation, and blood vessel dilation and blurring. Most interestingly however, renal tissue architecture remains preserved after RFA. This explains why conventional staining of ablated tissue may show seemingly untreated tissue and introduce false-positive interpretations of post-treatment biopsies.^21,22

Not only does RFA directly cause cellular death during treatment, but there is also a delayed effect of the ablation. Tan and associates²³ suggested that the tissue effects of RFA progress in two stages. Initial direct thermal ablation yields acute cell death, followed by a subacute and chronic phase that lasts 14 to 21 days and is caused by microvascular thrombosis, which results in further tissue infarction and coagulative necrosis. At the end of the chronic phase, a sharp demarcation between ablated and healthy tissue can be observed.²³ Several weeks after RFA, four zones can be distinguished microscopically from inside to outside: Complete necrosis, inflammatory infiltrate, hemorrhage, and fibrosis and regeneration.²⁴ Hsu and colleagues²⁵ showed that a tumor that was treated with RFA shows near complete resorption of coagulative necrosis after about 3 months.

As stated, it is difficult to unequivocally determine cell death in ablated tissue with H&E staining. Nicotinamide adenine dinucleotide (NADH) diaphorase staining is based on cellular viability rather than on histologic characteristics and is therefore superior to H&E staining in assessing viable cells after RFA.^26
–28 In tumors that are resected immediately after RFA, NADH staining still showed vital tumor cells in the ablation zone (tumor skipping).^12,15 The late effects of RFA, however, did not take place yet in these immediately resected specimens. This is illustrated by the fact that in one study, although tumor skipping (NADH-positive stains) has been described in a quarter of RCCs on immediate postablation biopsies, none of the studied patients experienced tumor recurrence after >2 years of follow-up.²⁹ Others have shown that inactivation of NADH diaphorase staining has been shown to take up to 2 hours after initial RFA treatment.³⁰ Therefore, the value of assessing ablation success using NADH diaphorase staining on tissues acquired immediately after RFA treatment is questionable.

NADH vital staining might, however, be useful in the assessment of longer-term follow-up biopsies of the ablation zone. Shah and coworkers²⁷ demonstrated that in late biopsies (>2 months postablation), H&E staining was shown to be unreliable (high false-positive rate) when correlated with NADH staining. The clinical significance of residual NADH-positive cells in follow-up biopsy, however, remains uncertain. In correlation to this subject, a recent study showed that the presence of a positive section margin after partial nephrectomy did not increase the long-term risk of local recurrence, metastatic progression, and cancer-specific survival.³¹ In 2007, Kwon and colleagues³² published similar results. Their study, however, showed that the significance of a positive section margin is correlated with the malignant potential of the initial tumor. The prognosis of tumors with a low malignant potential does not appear to be influenced by a positive section margin.

Postoperative follow-up imaging

Success of RFA is defined by the absence of contrast enhancement on postoperative cross-sectional imaging. Residual disease is defined as contrast enhancement on the first postoperative contrast-enhanced imaging, while recurrent disease is defined as reappearance of contrast enhancement after previous negative postoperative imaging.

Matin and associates³³ noted in a multicenter series that ±90% of radiologic recurrences were detected within the first 12 months after ablation. Therefore, they proposed a follow-up regimen of three to four imaging studies in the first 12 months after RFA at 1, 3, possibly 6, and 12 months after the treatment. On the other hand, Klingler and coworkers¹⁵ stated that the first postablation imaging should not be done within 3 months of treatment, because scar formation and reabsorption may lead to misinterpretation of the results.

Indeed, Matsumoto and associates³⁴ noted that lesions treated by RFA have unique radiographic features on contrast-enhanced CT imaging: Treated endophytic tumors developed a low density, nonenhancing, wedge-shaped defect that persisted during follow-up. Treated exophytic lesions were characterized by absence of contrast enhancement and sometimes minimal shrinkage with a preserved configuration compared with pretreatment imaging. Percutaneously treated lesions developed a peritumoral scar or halo that demarcated ablated and nonablated tissue. Persistent tumor was marked by contrast enhancement within the ablation margins of the original mass.

Recently, Davenport and colleagues³⁵ published similar findings on follow-up imaging after RFA. They confirmed the presence of a perilesional halo as a common feature post-RFA. An initial volume increase with subsequent decrease in lesion size was noted in small (<3 cm) lesions, a finding not seen in lesions larger than 3 cm. Schirmang and coworkers³⁶ also stated that a perilesional halo is a benign finding and is not to be mistaken for residual or recurrent tumor. Both Gervais and colleagues³⁷ and Wile and associates³⁸ pointed out that the presence of contrast-enhanced crescents or nodules within or next to the ablation site on follow-up contrast-enhanced CT or MRI suggest residual tumor.

Weight and coworkers³⁹ suggested a poor correlation between follow-up imaging and histopathology in RFA treated lesions. They showed a discerning amount of false-positive and false-negative imaging results when compared with a lesion biopsy after treatment. In a retrospective analysis, 6-month postablation biopsy reduced the success rate to 64.8% compared with 85% with imaging alone. Their study, however, was mainly flawed by the fact that they did not use NADH diaphorase staining to evaluate viability of tissue. Javadi and colleagues⁴⁰ also published false-negative and false-positive imaging results when correlated to postablation biopsies. Similarly, Park and associates⁴¹ described a false positive imaging result with no residual RCC in the subsequent resection specimen.

For the first year of post-therapy follow-up, contrast-enhanced imaging studies should be performed at 3, 6, and 12 months, because most incomplete ablations and recurrences occur within the first year. Imaging should not be performed within the first 3 months, because a halo sign can be misinterpreted as incomplete ablation.^34
–36 The jury is still out on whether a postablation biopsy should be implemented in routine follow-up in the absence of contrast enhancement within the ablated tumor. Considering all of the above, the clinical significance of skip lesions or viable cells on a follow-up biopsy with negative postoperative imaging are at least uncertain. Further research is needed to elucidate the natural history of viable tumor cells at follow-up biopsy. On the other hand, most authors agree that contrast enhancement within the ablated tumor necessitates further assessment with renal biopsy and re-treatment with RFA or salvage surgery when appropriate.

Intermediate-term oncologic outcomes

Systematic review of the literature

From the literature review, 11 studies that represented 755 patients and 868 tumors that were treated by RFA were selected and further analyzed for the above-mentioned variables. In 6 of the 11 studies, representing 375/755 (49.7%) patients, biopsy results were available and showed a 85% incidence of biopsy-proven RCC. The mean patient age was 69.3 years, which underlines the selection of patients who were elderly and mostly unfit for major surgery. The mean tumor diameter in the whole study group was 27.9 mm, which is well within the accepted limits of 3 cm for successful ablation. The mean duration of reported follow-up after RFA was 19.3 months.

The type of RFA system used varied between studies and even within studies. It is therefore impossible to assess the superiority of any specific system over another. What can be observed is that there were no clear differences in final success rates between the Tyco-Valleylab device (n = 104, mean lesion diameter 27 mm, mean follow-up 13.8 months, reablation rate 6.7%, mean final success 92.8%) and the RITA Medical Systems device (n = 84, mean lesion diameter 27 mm, mean follow-up 19.6 months, reablation rate 4.8%, mean final success 100%) in the only two studies in which 100% of the included patients had biopsy-proven RCC.^17,42 The approach was mainly percutaneous, with only 2/11 of the series partly consisting of open or laparoscopic cases. Mean follow-up ranged from 9 to 27.6 months, mean success after first ablation ranged from 67% to 100%, and mean final success (allowing one or two reablations) ranged from 89.7% to 100%. A summary of the included RFA studies is listed in Table 1.^{17,36,43

–50} Table 2 provides an overview of the patient and tumor characteristics and outcomes for the studies that were included.

Table 1.

Results of the Literature Study of Radiofrequency Ablation

Study	N patients/N tumors	Biopsy-proven RCC (%)	Type of RFA system used	Mean age (years)	Mean diameter (mm)	Approach	Mean follow-up (months)	Mean success after 1 session %	Final success %	2nd–3rd session N patients (%)
Salagierski 2006⁴³	42/45	NA	Tyco-Valleylab (Radionics) (n = 43)	68	37.5	PC	14	93.3	100	3 (7.1)
			Celon Olympic (n = 2)
Hegarty, 2006⁴⁴	72/81	NA	RITA Medical Systems (n = 81)	66.6	25.1	PC	12	91.4	93.8	2 (2.8)
Breen, 2007⁴⁵	97/105	NA	Tyco-Valleylab (Radionics) (n = 58)	71.7	32	PC	16.7	79.0	90.5	11 (11.3) – 1 (1.0)
			RITA Medical Systems (n = 47)
Veltri, 2009⁴⁶	68/87	NA	RITA Medical Systems (n = 70)	64.9	29	PC	24.4	86.2	89.7	3 (4.4)
			Boston Scientific (n = 17)
Schirmang, 2009³⁶	101/106	NA	NA	74	26	PC	25	94	92	4 (2.6)
Farrell, 2003⁴⁷	20/35	5.7	Tyco-Valleylab (Radionics) (n = 23, lesions >2 cm)	64	17	PC/open	9	100.0	100	0
			RITA Medical Systems (n = 12, lesions <2 cm))
Varkarakis, 2005⁴⁸	46/56	48.2	RITA Medical Systems (n = 31)	63.9	22	PC	27.5	83.9	96.4	6 (13.0)
			Boston Scientific (n = 25)
Carey, 2007⁴⁹	36/37	83.8	RITA Medical Systems (n = 21)	70.7	NA	PC/lap	11.3	94.6	97.3	1 (2.8)
			Tyco-Valleylab (Radionics) (n = 16)
Gervais, 2005⁵⁰	85/100	90.9	Tyco-Valleylab (Radionics) (n = 92)	70	32	PC	27.6	67.0	90.9	21 (24.7) – 2 (2.4)
			RITA Medical Systems (n = 8)
Zagoria, 2007⁴²	104/125	100	Tyco-Valleylab (Radionics) (n = 125)	70.4	27	PC	13.8	87.2	92.8	7 (6.7)
Gupta, 2009¹⁷	84/91	100	RITA Medical Systems (n = 91)	NA	27	PC	19.6	95.6	100	4 (4.8)

The box marks studies with only biopsy-proven renal-call carcinoma.

RCC = renal-cell carcinoma; RFA = radiofrequency ablation; PC = percutaneous; NA = not available; lap = laparoscopic.

Table 2.

Patient/Tumor Characteristics and Outcomes

	RFA
N patients	755
N tumors	868
Incidence of biopsy-proven RCC (%)	85.0^a
Mean patient age (y)	69.3^b
Mean tumor diameter (mm)	27.9^b
Mean duration of follow-up (mos)	19.3
Mean success after first ablation (%)	86.9
Mean final success (%)	93.8
Mean rate of repeated ablation (%)	8.6

All means were weighted for study size.

Data not available for 5/11 studies.

Data not available for 1/11 study.

RFA = radiofrequency ablation; RCC = renal-cell carcinoma.

When evaluating the results of the literature review, one should take into account that part of the tumors included in 9/11 series were benign. Studies describing the outcomes of RFA in an RCC-only population are scarce and are marked by the box in Table 1. Interestingly, the results of these RCC-only series did not differ from those that also included benign lesions. The analysis of the percentage of successful treatments as defined in Methods revealed a 86.9% success after one RFA session. The final success (after one or more sessions) of RFA was 93.8%. These results demonstrate that RFA is able to achieve adequate local tumor control regardless of histology.

Clinical predictors of success

Currently, about 95% of the reported renal RFA treatments have been performed using the percutaneous approach.⁵¹ A retrospective study that evaluated US-guided percutaneous RFA for renal tumors showed that tumor size was smaller in successfully treated tumors (P = 0.004) and that central growth was a negative predictive factor for technical success of RFA (P = 0.009).⁴⁶ Using multivariate analysis, Gervais and coworkers⁵⁰ found that small tumor size (P = 0.0001) and noncentral location (P = 0.0049) proved to be independent predictors of complete tissue necrosis after one RFA ablation session. Small tumors (<3cm) were completely ablated with 100% success, whereas the larger tumors (3–5 cm and >5 cm) were ablated with 92% and 25% rates of success, respectively. Large and/or central tumors are more likely to necessitate multiple or repeated ablations to achieve complete necrosis.

Zagoria and associates⁴² reported that CT-guided percutaneous RFA can accurately destroy RCCs smaller than 3.7 cm. RFA of larger RCCs will result in an increased risk of residual and recurrent RCC. Of the 125 treated RCCs, 116 (93%) were completely ablated (109 in one session, 7 after a second session). RFA achieved complete ablation in all 95 RCCs smaller than 3.7 cm and in 21 (70%) of the 30 larger tumors. In nine cases, there was evidence of residual RCC on follow-up scans. The final success rate after RFA determined in the current analysis (93.8%) in which 85.0% of the tumors were biopsy proven RCC is similar to the reported final success rate in the Zagoria and associates⁴² series (92.8%) in which all treated tumors were biopsy-proven RCC.

Varkarakis and coworkers⁴⁸ evaluated percutaneous CT-guided RFA for small renal tumors (<4 cm) at a 2-year mean follow-up. They found a success rate of 100% for noncentral tumors (39 of 39) and 82% (14 of 17) for central tumors (P < 0.05). The reason for this is probably the heat sink effect. The mean size of central tumors was significantly larger than that of noncentral tumors (2.6 cm vs 2.1 cm; P < 0.05).

Complications

A recent meta-analysis by Hui and colleagues¹⁶ including 46 series (28 percutaneous, 18 surgical) revealed that when ablating renal tumors, the percutaneous route was equally effective but safer than the open or laparoscopic approach. The major complication rate in the percutaneous treatment group was significantly lower than that in the surgical treatment group (3% vs 7%; P < 0.05). Johnson and associates⁵² analyzed complications of RFA in a multi-institutional review. The RFA group of 133 cases reported a total of 11 complications (8.3%) of which 8 (6%) were minor and 3 (2.2%) major. There was one death (aspiration pneumonia) that was not directly attributable to the RFA procedure. The most common complication in the review of Johnson and associates⁵² was pain or paresthesia at the probe insertion site. Of the 30 complications, 25 (83.3%) were directly attributable to the ablative procedure.

Complications can be attributed to the approach (percutaneous or laparoscopic) as well as to the ablation alone. Zagoria and colleagues⁴² analyzed the correlation between complications and side, location and growth of the tumor, and patient sex. They could not find any statistically significant association with increased likelihood of complications. A major concern with minimally invasive ablative treatments, especially for central tumors, is the risk for injury to the collecting system and surrounding vital structures.⁴⁴ Collecting system and bowel injuries after RFA can be avoided by better patient selection based on patient and tumor characteristics.⁵³ Medially-located tumors are more at risk of ureteral thermal injury.⁴⁶ Bowel-related complications after RFA are uncommon and can be avoided by applying hydrodissection for renal tumors that are close to the bowel.³⁷

Conclusions

Although there have been concerns about the oncologic efficacy of RFA in the management of SRM, the present analysis reveals that RFA has a high intermediate-term ablative success rate when accepting a reablation rate of 8% to 10 % and taking into account the selection of tumors that are largely below the 3-cm diameter threshold. Complications after RFA are less frequent and more often minor compared with surgical series. This is especially attractive in the growing elderly patient population with multiple comorbidities.

Crucial in deciding on ablative modalities is careful patient selection, taking into account both patient and tumor characteristics. A renal mass biopsy before treatment is mandatory, because it allows for accurate differentiation between benign and malignant lesions and it is important for result reporting. The jury is still out regarding the need for a routine follow-up biopsy in the case of absent contrast-enhancement in the ablation zone. Contrast enhancement within the ablated tumor necessitates further assessment with renal biopsy and re-treatment with RFA or salvage surgery when appropriate.

Special care should be taken to avoid ureteral damage in medially located lower pole tumors, and to avoid bowel injury in anteriorly located tumors. Long-term follow-up data are expected to confirm the role of RFA in the management of SRM.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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