Early experience with percutaneous radiofrequency ablation of small solid renal masses

Irreversible Electroporation: Defining the MRI Appearance of the Ablation Zone With Histopathologic Correlation in a Porcine Liver Model

OBJECTIVE

The purpose of this study is to evaluate the MRI appearance of the irreversible electroporation zone in porcine liver, with histopathologic correlation.

MATERIALS AND METHODS

Nine irreversible electroporation ablations were percutaneously created in two Yorkshire pigs. Irreversible electroporation was performed with a bipolar 16-gauge electrode with 3-cm exposure tip and fixed 8-mm interpolar distance. Gadoxetate disodium-enhanced 3-T MRI was performed 50 hours after irreversible electroporation. Livers were harvested immediately after MRI for histopathologic analysis. Ablation zone size was measured on each pulse sequence and correlated with pathologic ablation zone size. Qualitative MRI features of the ablation zone were assessed, and contrast-to-noise ratios (CNRs) were calculated. Statistical analysis included Pearson correlation and t tests.

RESULTS

Histopathologically, three distinct layers were present in the irreversible electroporation ablation zone: an inner layer of coagulative necrosis (hyperintense at T1- and T2-weighted imaging and nonenhancing), a middle layer of congestion and hemorrhage (hypointense at T1-weighted imaging, hyperintense at T2-weighted imaging and DWI, and progressively enhancing but hypointense at the hepatobiliary phase), and a peripheral layer of inflammation (hyperintense at the arterial phase but isointense at all other sequences). The hepatobiliary phase ablation zone size showed the highest correlation with the pathologic ablation zone size (r = 0.973). This correlation was significant (p < 0.001). T2-weighted imaging had the highest lesion-to-normal tissue CNR.

CONCLUSION

The irreversible electroporation ablation zone contains three distinct histopathologic zones, each with unique MRI features. T2-weighted imaging had the highest CNR, and the hepatobiliary phase had the strongest correlation with ablation zone size.

Percutaneous radiofrequency ablation: minimally invasive therapy for renal tumors

Currently, up to 60% of renal tumors are detected incidentally by abdominal imaging. Most of these tumors are small and localized to the kidney. Owing to the shift to lower stage at diagnosis, radical nephrectomy has fallen out of favor and has been replaced by nephron-sparing surgery. Currently, partial nephrectomy is the treatment of choice for patients with small renal tumors. As the trend towards less invasive therapy continues, laparoscopic and percutaneous ablation techniques have gained popularity for the treatment of renal tumors in patients who are high-risk surgical candidates, or have a solitary kidney, limited renal function or multifocal disease. Percutaneous radiofrequency ablation is a safe, minimally invasive treatment option for those patients.

Thermal ablation

Image-guided tumor ablation refers to a group of treatment modalities that have emerged during the past 2 decades as important tools in the treatment of a wide range of tumors throughout the body. Although most widely recognized in the treatment of hepatic and renal malignancies, the role of thermal ablation has expanded to include lesions of the lung, breast, prostate, bone, as well as other organs and its clinical applications continue to increase. In the following article, we discuss the major thermal ablation modalities, their respective strengths and weaknesses, potential complications and how to avoid them, as well as possible future applications.

MR imaging-guided interventions in the genitourinary tract: an evolving concept

MR imaging-guided interventions are well established in routine patient care in many parts of the world. There are many approaches, depending on magnet design and clinical need, based on MR imaging providing excellent inherent tissue contrast without ionizing radiation risk for patients. MR imaging-guided minimally invasive therapeutic procedures have advantages over conventional surgical procedures. In the genitourinary tract, MR imaging guidance has a role in tumor detection, localization, and staging and can provide accurate image guidance for minimally invasive procedures. The advent of molecular and metabolic imaging and use of higher strength magnets likely will improve diagnostic accuracy and allow targeted therapy to maximize disease control and minimize side effects.

Treatment of renal tumors by percutaneous ultrasound-guided radiofrequency ablation using a multitined electrode: effectiveness and complications

BACKGROUND

Radiofrequency ablation (RFA) is a minimally aggressive, therapeutic alternative for renal tumors. It can be an alternative to nephrectomy in patients with previous nephrectomy, bilateral tumors, von Hippel-Lindau disease, or small renal carcinomas and in those with contraindications for surgery.

OBJECTIVE

To assess the effectiveness of the treatment of renal tumors by RFA in the short and medium term and to identify the possible complications and the factors that determine therapeutic success.

DESIGN, SETTING, AND PARTICIPANTS

A retrospective review of patients with renal tumors treated with RFA between May 2005 and December 2008 was performed in a tertiary academic hospital. Patients were selected among those with previous nephrectomy, bilateral neoplasms, von Hippel-Lindau disease, surgical risk, comorbidity, advanced age, or patient's refusal to surgery. Tumors with evidence of extrarenal extension were excluded. Patients were followed up for 10-50 mo using computed tomography and magnetic resonance imaging.

INTERVENTION

Ultrasound-guided RFA was performed on 65 tumors (range: 1.2-5.3 cm) of 58 patients using multitined electrodes.

MEASUREMENTS

Incomplete ablation rate, therapeutic success rate, and complications rate.

RESULTS AND LIMITATIONS

Therapeutic success was achieved in 59 of 65 tumors (91%): 53 in a single session, 5 in two sessions, and 1 in three sessions. A significant relationship was observed between size and growth pattern of the tumor and both therapeutic success and incomplete ablation rates. Therapeutic success in tumors >5 cm was 60%. Complications were detected in 10 patients (13%); 5% were considered major complications. Limitations include the lack of pathologic studies to confirm a complete ablation and the lack of a control group to compare with the results of those who underwent nephrectomy.

CONCLUSIONS

RFA is safe and effective in renal tumors. Corticomedullary lesions and tumors >3 cm have greater possibility of incomplete ablation. In tumors >5 cm, RFA has a significant failure rate.

Biopsy of renal masses: when and why

Percutaneous image-guided biopsy of renal masses is a safe and accurate procedure. Although once reserved for the diagnosis of unresectable renal cell carcinoma, metastases, lymphoma, and infection, today percutaneous image-guided biopsy has an expanded role. There is increasing awareness that a substantial proportion of small, solid renal masses are benign neoplasms. Although imaging can be used to diagnose most of them, some are incorrectly believed to represent renal cell carcinoma and unnecessary surgery may be performed. Based largely on advances in cytological techniques, percutaneous biopsy can be now be used to diagnose benign neoplasms and thus prevent them from being treated unnecessarily. Concurrent advances in percutaneous ablation have also promoted its use. As a result, there are 8 established indications for percutaneous biopsy, and reason to believe that the number of indications will expand further in the future.

Cryoablation or radiofrequency ablation of the small renal mass : a meta-analysis

BACKGROUND

The incidence of renal cell carcinoma is rising because of incidental detection of small renal masses (SRMs). Although surgical resection remains the standard of care, cryoablation and radiofrequency ablation (RFA) have emerged as minimally invasive treatment alternatives. The authors of this report performed a comparative meta-analysis evaluating cryoablation and RFA as primary treatment for SRMs.

METHODS

A search of the MEDLINE database was performed reviewing the world literature for clinically localized renal masses treated by cryoablation or RFA.

RESULTS

Forty-seven studies representing 1375 kidney lesions treated by cryoablation or RFA were analyzed. No differences were detected between ablation modalities with regard to mean patient age (P = .17), tumor size (P = .12), or duration of follow-up (P = .53). Pretreatment biopsy was performed more often for cryoablated lesions (82.3%) than for RFA (62.2%; P < .0001). Unknown pathology occurred at a significantly higher rate for SRMs that underwent RFA (40.4%) versus cryoablation (24.5%; P < .0001). Repeat ablation was performed more often after RFA (8.5% vs 1.3%; P < .0001), and the rates of local tumor progression were significantly higher for RFA (12.9% vs 5.2%; P < .0001) compared with cryoablation. The higher incidence of local tumor progression was found to be correlated significantly with treatment by RFA on univariate analysis (P = .001) and on multivariate regression analysis (P = .003). Metastasis was reported less frequently for cryoablation (1.0%) versus RFA (2.5%; P = .06). Cryoablation usually was performed laparoscopically (65%), whereas 94% of lesions that were treated with RFA were approached percutaneously.

CONCLUSIONS

Ablation of SRMs is a viable strategy based on short-term oncologic outcomes. Although extended oncologic efficacy remains to be established for ablation modalities, the current data suggest that cryoablation results in fewer retreatments and improved local tumor control, and it may be associated with a lower risk of metastatic progression compared with RFA.

Renal thermal ablative therapy

Energy targeting is greatly enhanced through imaging modalities, which greatly assist needle placement or energy delivery to the optimal location for maximal effectiveness. When vital structures obscure access to the renal lesion, laparoscopic mobilization of these structures with direct visualization of the tumor can increase the likelihood of ablation success and minimize complication risk. Ablative therapies are attractive because of their minimal impact on patient quality of life in addition to their morbidity and cost. Although they show promise of efficacy, they must be evaluated with long-term follow-up before they are considered the standard of oncologic care. Renal masses can be treated with a laparoscopic or percutaneous approach depending on tumor location, size, and the available technology and experience of the center.

Radiofrequency ablation of renal tumors

Development of cross-sectional imaging has led to a significant increase in diagnosis of small renal tumors. Nephron-sparing surgery has proven to be effective in the management of these small tumors. Could radiofrequency ablation be as effective in the management of these patients, after showing promising results in a selected group of patients? In this article we discuss the principles of radiofrequency ablation and present results in a selected group of patients. We also outline future perspectives of this noninvasive technique.

MR imaging-guided interventions in the genitourinary tract: an evolving concept

MR imaging-guided interventions are well established in routine patient care in many parts of the world. There are many approaches, depending on magnet design and clinical need, based on MR imaging providing excellent inherent tissue contrast without ionizing radiation risk for patients. MR imaging-guided minimally invasive therapeutic procedures have advantages over conventional surgical procedures. In the genitourinary tract, MR imaging guidance has a role in tumor detection, localization, and staging and can provide accurate image guidance for minimally invasive procedures. The advent of molecular and metabolic imaging and use of higher strength magnets likely will improve diagnostic accuracy and allow targeted therapy to maximize disease control and minimize side effects.

Imaging appearances following thermal ablation

Radiofrequency ablation (RFA) has an increasingly important role in the management of a number of solid tumours. Treatments usually take place at specialist centres that draw patients from a wide geographical area, but follow-up imaging is often undertaken at the referring institution. This review aims to describe and illustrate the range of normal and abnormal post-ablative appearances encountered in the most commonly treated organs, i.e. liver, lung, and kidney, to equip radiologists with the necessary knowledge for confident interpretation of post-ablation imaging in this diverse patient group.

Intermediate comparison of partial nephrectomy and radiofrequency ablation for clinical T1a renal tumours

OBJECTIVE

To compare the intermediate-term outcomes of patients with clinical T1a renal tumours who were treated with nephron-sparing surgery by partial nephrectomy (PN), the preferred approach for small (cT1a) renal tumours, or radiofrequency ablation (RFA), recently offered to selected patients as an alternative, less morbid technique.

PATIENTS AND METHODS

We identified patients with stage T1a renal masses who had > or = 2 years of follow-up; those with bilateral synchronous or metachronous tumours, metastatic disease at presentation, or a family history of renal cell carcinoma were excluded. From July 1996 to January 2004 110 PNs were identified in our database; 37 patients who fulfilled the inclusion criteria had either open (30) or laparoscopic PN (seven) and 40 had either percutaneous (26) or laparoscopic (14) RFA.

RESULTS

The mean (range) follow-up for the RFA and PN groups was 30 (18-42) and 47 (24-93) months, respectively; the respective mean tumour size was 2.41 and 2.43 cm. There was one incomplete ablation and two local recurrences in the RFA group, and two recurrences in the PN group (one local and one in the contralateral kidney). There were no disease-specific deaths. The overall actuarial disease-free probability for the PN and RFA groups, respectively, was 95.8% and 93.4% (P = 0.67).

CONCLUSIONS

This initial 3-year actuarial analysis showed that RFA for cT1a renal tumours has comparable oncological outcomes to PN; however, longer term data are still needed.

Laparoscopic Management of Renal Tumors

Laparoscopy has become commonplace in the management of genitourinary malignancies and, in some institutions, has largely replaced open surgery as the primary treatment method for renal tumors. Outside of laparoscopic radical nephrectomy, other modalities, such as nephron-sparing partial nephrectomy and energy-based ablative procedures, have been extended to laparoscopy. In this article, we present our experience and review the literature regarding the utility of laparoscopy in the management of renal tumors.

Ablative techniques for the management of kidney cancer

For lesions smaller than 4 cm, nephron-sparing surgery has been shown to be oncologically equivalent to radical nephrectomy, albeit with the advantage of preservation of overall renal function. As such, partial nephrectomy became the first-line treatment option for localized, small renal masses. Minimally invasive options associated with limited morbidity--such as probe-ablative procedures--are, however, being investigated in selected patients for whom invasive, nephron-sparing surgery (whether laparoscopic or open) is undesirable. The main probe-ablative techniques being investigated as alternatives to partial nephrectomy are cryoablation, radiofrequency ablation, and high-intensity focused ultrasound. Advances in imaging, ablative system technologies, and early evidence that in situ tumor ablation can yield comparable results to those achieved with tumor resection in selected cases, have sparked significant interest in these minimally invasive techniques.

Bimodal electric tissue ablation (BETA) — in-vivo evaluation of the effect of applying direct current before and during radiofrequency ablation of porcine liver

AIM

To examine the effect of applying increasing amounts of direct current (DC) before and during alternating current radiofrequency ablation of porcine liver.

MATERIALS AND METHODS

Using a Radiotherapeutics RF3000 generator, a 9 V AC/DC transformer and a 16 G plain aluminium tube as an electrode, a control group of 24 porcine hepatic radiofrequency ablation zones was compared with 24 zones created using a bimodal electric tissue ablation (BETA) technique in three pigs. All ablations were terminated when tissue impedance rose to greater than 999 Omega or radiofrequency energy input fell below 5 W on three successive measurements taken at 1 min intervals. BETA ablations were performed in two phases: an initial phase of variable duration DC followed by a second phase during which standard radiofrequency ablation was applied simultaneously with DC. During this second phase, radiofrequency power input was regulated by the feedback circuitry of the RF3000 generator according to changes in tissue impedance. The diameters (mm) of each ablation zone were measured by two observers in two planes perpendicular to the plane of needle insertion. The mean short axis diameter of each ablation zone was subjected to statistical analysis.

RESULTS

With increased duration of prior application of DC, there was a progressive increase in the diameter of the ablation zone (p<0.001). This effect increased sharply up to 300 s of pre-treatment after which a further increase in diameter occurred, but at a much lesser rate. A maximum ablation zone diameter of 32 mm was produced (control diameters 10-13 mm).

CONCLUSION

Applying a 9 V DC to porcine liver in vivo, and continuing this DC application during subsequent radiofrequency ablation, results in larger ablation zone diameters compared with radiofrequency ablation alone.

Nonablative radiofrequency for facial and neck rejuvenation. A faster, safer, and less painful procedure based on concentrating the heat in key areas: the ThermaLift concept

Nonablative radiofrequency was the first method of noninvasive tissue contraction. It is a safe and effective method, although the results are modest when compared with plastic surgery. Patients like the fact that it requires no down time, it is performed with topical anesthesia, and it can be combined with numerous other modalities of skin rejuvenation. Technique and results are discussed.

Experiences in US-Guided Percutaneous Radiofrequency Ablation of 44 Renal Tumors in 31 Patients: Analysis of Predictors for Complications and Technical Success

PURPOSE

Preliminary clinical studies have shown the feasibility, safety, and efficacy of radiofrequency thermal ablation (RFA) of renal tumors, but only a few have analyzed the prognostic factors for technical success and there are no long-term results. Our objective was to statistically evaluate our mid-term results of percutaneous US-guided RFA in order to define predictors for complications and technical success.

METHODS

We selected for treatment 44 tumors in 31 patients (24 with renal cell carcinoma, 7 with hereditary tumors, 15 with a solitary kidney), up to 5 cm in diameter.

RESULTS

Eight adverse events occurred; 3 (6.8%) were major complications, successfully treated with interventional radiology procedures in 2 cases. Exophytic extension of the tumor was protective against complications (p = 0.040). Technical success was obtained in 38 lesions after one RFA session and in 39 (89%) after one more session, when possible. At the end of treatment, central extension was the only negative predictor for technical success (p = 0.007), while neither size >3 cm (p = 0.091) nor other prognostic factors were statistically significant.

CONCLUSION

US-guided percutaneous RFA can be proposed for non-central renal tumors up to 5 cm, also in patients without surgical contraindications, thanks to a low incidence of complications and a high success rate. Randomized controlled trials versus surgery are now needed to investigate long-term comparative results.

Imaging Associated with Percutaneous and Intraoperative Management of Renal Tumors

As new minimally invasive treatment options for small renal tumors such as laparoscopic partial nephrectomy (LPN), radiofrequency ablation (RFA), and cryoablation(CA) have been developed, the reliance upon imaging technologies, both intraoperatively and postoperatively, has expanded greatly. CT, MRI, and ultrasonography (US)have proven themselves extremely useful in this regard, but their utility requires a thorough understanding of each modality's limitations, proper intraoperative use, and expected postoperative findings. This article discusses intraoperative use of US for LPN,RFA, and CA. The expected postoperative MRI and CT findings after CA and RFA also are covered, highlighting the different radiographic evolutionary patterns encountered after use of these technologies. Because the success of these new treatments for small re-nal tumors (especially RFA and CA) depends not only on the technology itself but also on the advantages and limitations of the associated radiographic techniques, urologists of the 21st century must be facile at interpreting and manipulating these imaging modalities to appropriately care for their renal tumor patients.

Percutaneous radiofrequency ablation of renal tumors: Midterm results in 16 patients

PURPOSE

To evaluate the outcome of 16 patients after percutaneous radiofrequency ablation of renal tumors.

MATERIALS AND METHODS

Sixteen patients (nine women, seven men; mean age, 61+/-9 years) with 24 unresectable renal tumors (mean volume, 4.3+/-4.3 cm3) underwent CT-guided (n=20) or MR imaging-guided (n=4) percutaneous radiofrequency ablation using an expandable electrode (Starburst XL, RITA Medical Systems, Mountain View, CA) with a 150-W generator. The initial follow-up imaging was performed within 1-30 days after RF ablation, then at 3-6 month intervals using either CT or MRI. Residual tumor volume and coagulation necrosis was assessed, and statistical correlation tests were obtained to determine the strength of the relationship between necrosis volume and number of ablations.

RESULTS

Overall, 97 overlapping RF ablations were performed (mean, 3.5+/-1.5 ablations per tumor) during 24 sessions. Five or more RF ablations per tumor created significant larger necrosis volumes than 1-2 (p=.034) or 3-4 ablations (p=.020). A complete ablation was achieved in 20/24 tumors (primary technical success, 83%; mean volume of coagulation necrosis: 10.2+/-7.2 cm3). Three of four residual tumors were retreated and showed complete necrosis thereafter. Three major complications (one percuatneous urinary fistula and two ureteral strictures) were observed after RF ablation. No further clinically relevant complications were observed and renal function remained stable. During a mean follow-up of 11.2 months (range, 0.2-31.5), 15/16 patients (94%) were alive. Only one patient had evidence of local recurrent tumor.

CONCLUSION

The midterm results of percutaneous RF ablation for renal tumors are promising and show that RF ablation is well-suited to preserve renal function.

Review of minimally invasive renal therapies: Needle-based and extracorporeal

Management of the small renal mass (< or = 3 cm) is a topic of significant debate among urologists worldwide. With the advent of needle-based therapies and, less frequently, reports of extracorporeal approaches, along with ongoing refinements in each technology, patients with such masses may have the option of being treated in a truly minimally invasive, or even noninvasive, manner. Herein we review the body of available clinical literature on these modalities with respect to patient selection, success and complication rates, follow-up information, energy delivery devices, and current probe configurations.

Renal Masses in the Adult Patient: The Role of Percutaneous Biopsy

Although percutaneous renal mass biopsy with cross-sectional imaging guidance has long been considered to be safe and accurate, there have been recent advances in imaging, interventional, and cytologic techniques that have increased the role of percutaneous biopsy in the diagnosis of renal masses. Today, biopsy plays a fundamental role in the care of patients with a renal mass. Biopsy results are used to confirm the diagnosis of renal cancers, metastases, and infections, and there is increasing evidence to suggest that biopsy can help subtype and grade many primary renal cancers. Because a considerable fraction of small solid renal masses are benign and do not need treatment, there is an increasing need to diagnose them. Biopsy after a full imaging work-up can help prevent unnecessary and potentially morbid surgical and ablation procedures in a substantial number of patients. Although more data are needed to understand the overall accuracy of biopsy for the diagnosis of benign lesions, many can be diagnosed with the aid of biopsy findings. This article reviews reported experience with percutaneous renal mass biopsy, discusses the technical factors that contribute to results, and details seven specific clinical settings that should prompt the clinician to consider percutaneous biopsy when encountering a renal mass.

MRI-guided percutaneous cryoablation of renal tumors: use of external manual displacement of adjacent bowel loops

PURPOSE

We sought to investigate retrospectively the safety and effectiveness of using external hand compression to displace adjacent bowel loops during MRI-guided percutaneous cryoablation of renal tumors.

MATERIALS AND METHODS

Fourteen patients (six women, eight men; mean age: 72 years) with 15 renal tumors (mean diameter: 2.4 cm; range: 1.4-4.6 cm) adjacent to bowel were treated with MRI-guided percutaneous cryoablation during which bowel was displaced manually. Bowel loop of concern was ascending colon (n=5), descending colon (n=8), descending colon and small bowel (n=1), ascending colon and small bowel (n=1). To analyze effectiveness of the maneuver, mean distance between tumor margin and bowel before and after the maneuver were compared and analyzed using paired Student's t-test. Minimum distance between iceball edge and adjacent bowel with external manual displacement during freezing was also measured. Safety was assessed by analyzing post-procedural MR imaging for adjacent bowel wall thickening and focal fluid collections as well as patients' clinical and imaging follow-up.

RESULTS

Mean distance between tumor margin and closest adjacent bowel increased from 0.8 cm (range: 0-2 cm) before external manual compression to 2.6 cm (range: 1.6-4.1 cm) with manual displacement (p<0.01). Mean minimum distance between iceball edge and closest adjacent bowel during the procedures was 1.6 cm (range: 0.5-3.5 cm). No evidence of bowel injury was encountered. Twelve of 15 tumors had follow-up (mean: 10 months) that showed no tumor recurrence.

CONCLUSION

MRI-guided percutaneous cryoablation of renal tumors adjacent to bowel can be done safely and effectively using external hand compression to displace bowel loops.

Treatment of renal tumors with radiofrequency ablation

BACKGROUND

Radiofrequency (RF) energy has been investigated as a minimally invasive modality for ablating small renal tumors. Recent advances in the application of this technology have improved its safety and effectiveness.

MATERIALS AND METHODS

We describe the technology of RF application and review the current delivery systems as applied to renal tumor ablation. We also review relevant animal studies, which have revealed the natural history of ablated renal tissue. Finally, we examine recent human trials with an emphasis on longer-term follow-up, imaging, complications, and successful ablation according to tumor location within the kidney; i.e., central v peripheral.

RESULTS

Radiofrequency ablation can be performed safely in a minimally invasive fashion either percutaneously or laparoscopically. Energy delivery varies, and available systems include dry, wet, cooled-tip, and bipolar electrodes. Heat rise and subsequent charring in the tissue adjacent to the electrode is limited by temperature or impedance-based feedback systems. In animal studies, ablation results in complete cell kill, as judged by nicotinamide adenine dinucleotide diaphorase staining. Clinical trials with intermediate follow-up show excellent success rates. Tumors >3 cm and central tumors have a higher recurrence rate after RFA than smaller, more peripheral tumors.

CONCLUSIONS

The current literature suggests that RFA is a promising minimally invasive method of treating small renal tumors. Nevertheless, long-term follow-up is still required, and questions remain regarding the optimal delivery system, duration of ablation, and method of surveillance.

Radiofrequency ablation of renal cell carcinoma: part 1, Indications, results, and role in patient management over a 6-year period and ablation of 100 tumors

OBJECTIVE

The objectives of our article are to review our experience with radiofrequency ablation of renal cell carcinoma and to assess size and location as predictors of the ability to achieve complete necrosis by imaging criteria.

MATERIALS AND METHODS

Over a 6-year period, 100 renal tumors in 85 patients underwent radiofrequency ablation at a single institution. The absence of enhancement on CT or MRI after radiofrequency ablation was interpreted as complete coagulation necrosis. Results were analyzed by tumor size and location using multivariate analysis. A p value of 0.05 or less was considered significant.

RESULTS

All 52 small (3 cm) and all 68 exophytic tumors underwent complete necrosis regardless of size, although many large tumors (> 3 cm) required a second ablation session. Using multivariate analysis, we found that both small size (p < 0.0001) and noncentral location (p = 0.0049) proved to be independent predictors of complete necrosis after a single ablation session. Location was a significant predictor (p = 0.015) of complete necrosis after any number of sessions, whereas size showed a strong trend (p = 0.059) toward predicting success after any number of sessions. Complications were either self-limited or readily treated and included hemorrhage (major, n = 2; minor, n = 3), inflammatory track mass (n = 1), transient lumbar plexus pain (n = 2), ureteral injury (n = 2), and skin burns (n = 1).

CONCLUSION

Radiofrequency ablation is a promising minimally invasive therapy for renal cell carcinoma in patients who are not good operative candidates. Small size and noncentral location are favorable tumor characteristics, although large tumors can sometimes be successfully treated with multiple ablation sessions.

Radiofrequency ablation of renal cell carcinoma: part 2, Lessons learned with ablation of 100 tumors

OBJECTIVE

The objective of our study was to review radiofrequency ablation of 100 renal tumors and lessons learned with respect to electrode approach, effects on collecting system, bowel proximity, and patterns of residual disease.

MATERIALS AND METHODS

Over 6 years, 100 renal tumors in 85 patients underwent radiofrequency ablation. Images were reviewed to determine the following: effect of initial electrode approach at and parallel to the tumor-kidney interface; effect of collecting system proximity to the tumor and to the zone of ablation; bowel proximity to the tumor and strategies to protect bowel; patterns of residual disease; and approaches at subsequent sessions.

RESULTS

The initial placement of the electrode at and parallel to the tumor-kidney interface did not result in significantly fewer overlapping ablations (p = 0.91) or a lower rate of residual disease (p = 0.86). Direct contiguity of tumor or zone of ablation to the collecting system did not increase the complication rate. However, obscuration of calyces by a central tumor was a significant predictor of collecting system hemorrhage necessitating treatment (p < 0.001) seen in three of nine tumors obscuring calyces. Clinically significant urine leaks were rare (1/100) and related to downstream obstruction. There were no bowel complications despite the fact that 27 of the tumors were within 1 cm of bowel. Protective strategies progressed from reliance on electrode positioning to hydrodissection. Residual patterns were predominantly nodules or crescents, and straight electrodes were commonly used to approach residual disease.

CONCLUSION

Initial electrode position at and parallel to the tumor-kidney interface does not result in less difficult or more successful ablations. Contiguity of tumor or zone of ablation to the collecting system does not increase the risk of complications, but obscuration of calyces does. Bowel complications are rare, and protection with hydrodissection is becoming more common. Residual tumor presents as nodules or crescents of persistent enhancement.

Percutaneous radiofrequency ablation of renal tumors: technique, complications, and outcomes

PURPOSE

To report the safety, technical success, and effectiveness of percutaneous radiofrequency (RF) ablation for renal tumors.

MATERIALS AND METHODS

The authors retrospectively reviewed the medical records and imaging studies of 29 consecutive patients (18 men, 11 women; mean age, 65 +/- 2.62 years) with 30 renal tumors (mean diameter, 3.5 +/- 0.24 cm) who underwent percutaneous RF ablation at their institution from September 2001 to March 2004. All procedures were performed with computed tomography guidance with general anesthesia, and all patients were admitted to the hospital for overnight observation. Technical success, complications, and their management were recorded. Technique effectiveness was assessed by imaging and clinical follow up.

RESULTS

Overall, 88 overlapping ablations were performed (mean, 2.6 +/- 0.16 ablations per tumor per session) in 34 sessions. There were four major complications (12%). Three patients had gross hematuria and urinary obstruction, all were successfully treated. One patient had persistent anterior abdominal wall weakness. There were also two minor complications (6%) without significant clinical sequelae. One patient had gross hematuria which resolved spontaneously, another patient had transient paresthesia of the anterior abdominal wall. There were no significant changes in renal function after RF ablation. The intent of RF ablation was eradication of the primary tumor in 27 patients and treatment of gross hematuria in the other two. Technical success was achieved in all cases. Follow-up images were available for 26 patients. The primary tumor was completely ablated in 23 of 24 patients (96%) in whom eradication of the primary tumor was attempted (follow up period: mean, 10 months, median 7 months). The two patients treated for hematuria remained asymptomatic for 6 and 27 months each.

CONCLUSION

Percutaneous RF ablation for renal tumors is safe and well tolerated. High technical success rates are expected. Early reports of the technique's effectiveness are promising.

MR imaging follow-up after percutaneous radiofrequency ablation of renal cell carcinoma: findings in 18 patients during first 6 months

PURPOSE

To prospectively evaluate the magnetic resonance (MR) imaging findings seen within the first 6 months after radiofrequency (RF) thermal ablation of renal cell carcinoma (RCC).

MATERIALS AND METHODS

After providing written informed consent, 18 patients (17 men, one woman; mean age, 71.2 years) with RCC underwent MR imaging-guided percutaneous RF thermal ablation, which was performed by using protocols approved by a comprehensive cancer center protocol committee and the institutional review board for human investigation. The study was Health Insurance Portability and Accountability Act compliant. Follow-up unenhanced T2-weighted MR images and unenhanced and gadolinium-enhanced T1-weighted MR images were acquired immediately, 2 weeks, 3 months, and 6 months after ablation. Thermal ablation zone size was analyzed, and contrast-to-noise ratios (CNRs) were calculated from the signal amplitudes of the thermal ablation zone, perirenal fat, and normal renal cortex on the MR images. Statistical analyses were performed by using the paired Student t test. P < .05 was considered to indicate statistical significance.

RESULTS

The mean follow-up time was 16.1 months (range, 6.0-41.2 months). The mean sizes of the thermal ablation zones were 6.8, 7.0, 6.1, and 4.7 cm2, respectively, at immediate, 2-week, 3-month, and 6-month follow-up MR imaging examinations. Thermal ablation zones were uniformly hypointense and had a surrounding bright rim on T2-weighted images and were predominantly hyperintense on T1-weighted images. Thin rim enhancement with central hypointensity was noted on the gadolinium-enhanced images. Gadolinium-enhanced T1-weighted and unenhanced T2-weighted MR images showed significantly higher CNRs than unenhanced T1-weighted MR images. Residual tumor was detected after RF thermal ablation in two cases and was best seen on unenhanced T2-weighted and gadolinium-enhanced T1-weighted MR images.

CONCLUSION

After initially increasing in size within the first 2 weeks, renal RF thermal ablation zones involuted during the remainder of the MR imaging follow-up period.

Concepts, Considerations, and Concerns on the Cutting Edge of Radiofrequency Ablation

Radiofrequency (RF) ablation is rapidly expanding from a tool to treat isolated hepatic malignancy to a therapy for patients with renal, adrenal, skeletal, breast, lung, and other soft-tissue neoplasms. The purpose of this article is to review the status of RF ablation outside the liver and lung and compare outcomes with current clinical standards when appropriate. The author also reviews how differences in local tissue environments play a role in creation of a thermal lesion and achievement of subsequent clinical success.

Percutaneous radiofrequency ablation of renal cell carcinoma

Conventional curative therapy for renal cell carcinoma has been open nephrectomy. However, several less invasive and/or nephron-sparing procedures have been developed as alternatives in selected patients. The newest of these therapeutic modalities involves percutaneous image-guided ablation with straight or expandable needle applicators that deposit energy. Radiofrequency ablation is the modality for which there is the largest reported experience with percutaneous application, and involves the use of electrical current to generate frictional heating of tissue. Animal studies confirm the ability of radiofrequency ablation to cause regions of necrosis within normal kidney and in VX2 tumors. Clinically, radiofrequency ablation of small renal cell carcinoma is increasingly being performed in selected patients who are not ideal surgical candidates. Results are excellent for small exophytic tumors, but successful treatment is less likely as tumor size increases or the location becomes more central. Complete treatment of most tumors requires one or more overlapping ablations with the needle electrodes positioned so as to cause necrosis in the entire volume of tumor. The number of overlapping ablations and the position of the needle electrodes vary based on tumor size and geometry. For very large tumors, pre-ablation catheter embolization may enhance the results of ablation by decreasing blood flow and perfusion mediated cooling. Following ablation, imaging with CT or MR is performed to assess the result and to diagnose any residual tumor so that it can be treated. Because the tumor remains in situ, imaging follow-up continues indefinitely. The complication rate of radiofrequency ablation is favorable when compared to surgical techniques. Long-term survival data are not yet available.

Clinical impact of incidental diagnosis of disease on non-contrast-enhanced helical CT for acute ureteral colic

The role of un enhanced helical CT (UHCT) in the evaluation of acute flank pain suggestive of urinary tract calculi is increasingly appreciated in the last few years. Recent studies have identified the advantages of UHCT in recognizing alternative findings within or outside the urinary tract. These incidental diagnoses on UHCT alter a patient's management and demonstrate the pivotal role of UHCT in rapidly triaging these patients for appropriate management. Clinical impact of incidental diagnoses is maximal in identifying alternate emergent conditions mimicking reno-ureteric colic and in identifying malignancies at an early stage when they are potentially curable.

Differentiation of Renal Clear Cell Carcinoma and Renal Papillary Carcinoma Using Quantitative CT Enhancement Parameters

OBJECTIVE

The purpose of our study was to evaluate quantitative multiphasic CT enhancement patterns of malignant renal neoplasms to enable lesion differentiation by their enhancement characteristics. We used a new method to standardize enhancement measurement in lesions on multiphasic CT not being influenced by intrinsic factors like cardiac output.

CONCLUSION

The new correction method is a simple tool for excluding intrinsic influences on the enhancement of lesions. Quantitative enhancement evaluation with this method of the influence of intrinsic factors enables accurate differentiation between renal clear cell carcinoma and renal papillary carcinoma.