Tissue Ablation: Applications and Perspectives

Tissue ablation techniques have emerged as a critical component of modern medical practice and biomedical research, offering versatile solutions for treating various diseases and disorders. Percutaneous ablation is minimally invasive and offers numerous advantages over traditional surgery, such as shorter recovery times, reduced hospital stays, and decreased healthcare costs. Intra-procedural imaging during ablation also allows precise visualization of the treated tissue while minimizing injury to the surrounding normal tissues, reducing the risk of complications. Here, the mechanisms of tissue ablation and innovative energy delivery systems are explored, highlighting recent advancements that have reshaped the landscape of clinical practice. Current clinical challenges related to tissue ablation are also discussed, underlining unmet clinical needs for more advanced material-based approaches to improve the delivery of energy and pharmacology-based therapeutics.

Time conditioning for arbitrary contrast phase generation in interventional computed tomography

Minimally invasive ablation techniques for renal cancer are becoming more popular due to their low complication rate and rapid recovery period. Despite excellent visualisation, one drawback of the use of computed tomography (CT) in these procedures is the requirement for iodine-based contrast agents, which are associated with adverse reactions and require a higher x-ray dose. The purpose of this work is to examine the use of time information to generate synthetic contrast enhanced images at arbitrary points after contrast agent injection from non-contrast CT images acquired during renal cryoablation cases. To achieve this, we propose a new method of conditioning generative adversarial networks with normalised time stamps and demonstrate that the use of a HyperNetwork is feasible for this task, generating images of competitive quality compared to standard generative modelling techniques. We also show that reducing the receptive field can help tackle challenges in interventional CT data, offering significantly better image quality as well as better performance when generating images for a downstream segmentation task. Lastly, we show that all proposed models are robust enough to perform inference on unseen intra-procedural data, while also improving needle artefacts and generalising contrast enhancement to other clinically relevant regions and features.

Present and future of metal nanoparticles in tumor ablation therapy

Cancer is an important factor affecting the quality of human life as well as causing death. Tumor ablation therapy is a minimally invasive local treatment modality with unique advantages in treating tumors that are difficult to remove surgically. However, due to its physical and chemical characteristics and the limitation of equipment technology, ablation therapy cannot completely kill all tumor tissues and cells at one time; moreover, it inevitably damages some normal tissues in the surrounding area during the ablation process. Therefore, this technology cannot be the first-line treatment for tumors at present. Metal nanoparticles themselves have good thermal and electrical conductivity and unique optical and magnetic properties. The combination of metal nanoparticles with tumor ablation technology, on the one hand, can enhance the killing and inhibiting effect of ablation technology on tumors by expanding the ablation range; on the other hand, the ablation technology changes the physicochemical microenvironment such as temperature, electric field, optics, oxygen content and pH in tumor tissues. It helps to stimulate the degree of local drug release of nanoparticles and increase the local content of anti-tumor drugs, thus forming a synergistic therapeutic effect with tumor ablation. Recent studies have found that some specific ablation methods will stimulate the body's immune response while physically killing tumor tissues, generating a large number of immune cells to cause secondary killing of tumor tissues and cells, and with the assistance of metal nanoparticles loaded with immune drugs, the effect of this anti-tumor immunotherapy can be further enhanced. Therefore, the combination of metal nanoparticles and ablative therapy has broad research potential. This review covers common metallic nanoparticles used for ablative therapy and discusses in detail their characteristics, mechanisms of action, potential challenges, and prospects in the field of ablation.

Multi-phase synthetic contrast enhancement in interventional computed tomography for guiding renal cryotherapy

PURPOSE

Minimally invasive treatments for renal carcinoma offer a low rate of complications and quick recovery. One drawback of the use of computed tomography (CT) for needle guidance is the use of iodinated contrast agents, which require an increased X-ray dose and can potentially cause adverse reactions. The purpose of this work is to generalise the problem of synthetic contrast enhancement to allow the generation of multiple phases on non-contrast CT data from a real-world, clinical dataset without training multiple convolutional neural networks.

METHODS

A framework for switching between contrast phases by conditioning the network on the phase information is proposed and compared with separately trained networks. We then examine how the degree of supervision affects the generated contrast by evaluating three established architectures: U-Net (fully supervised), Pix2Pix (adversarial with supervision), and CycleGAN (fully adversarial).

RESULTS

We demonstrate that there is no performance loss when testing the proposed method against separately trained networks. Of the training paradigms investigated, the fully adversarial CycleGAN performs the worst, while the fully supervised U-Net generates more realistic voxel intensities and performed better than Pix2Pix in generating contrast images for use in a downstream segmentation task. Lastly, two models are shown to generalise to intra-procedural data not seen during the training process, also enhancing features such as needles and ice balls relevant to interventional radiological procedures.

CONCLUSION

The proposed contrast switching framework is a feasible option for generating multiple contrast phases without the overhead of training multiple neural networks, while also being robust towards unseen data and enhancing contrast in features relevant to clinical practice.

Imaging considerations for thermal and radiotherapy ablation of primary and metastatic renal cell carcinoma

Ablative (percutaneous and stereotactic) thermal and radiotherapy procedures for management of both primary and metastatic renal cell carcinoma are increasing in popularity in clinical practice. Data suggest comparable efficacy with lower cost and morbidity compared to nephrectomy. Ablative therapies may be used alone or in conjunction with surgery or chemotherapy for treatment of primary tumor and metastatic disease. Imaging plays a crucial role in pre-treatment selection and planning of ablation, intra-procedural guidance, evaluation for complications, short- and long-term post-procedural surveillance of disease, and treatment response. Treatment response and disease recurrence may differ considerably after ablation, particularly for stereotactic radiotherapy, when compared to conventional surgical and chemotherapies. This article reviews the current and emerging role of imaging for ablative therapy of renal cell carcinoma.

Lung Ablation with Irreversible Electroporation Promotes Immune Cell Infiltration by Sparing Extracellular Matrix Proteins and Vasculature: Implications for Immunotherapy

Background: This study investigated the sparing of the extracellular matrix (ECM) and blood vessels at the site of lung irreversible electroporation (IRE), and its impact on postablation T cell and macrophage populations. Materials and Methods: Normal swine (n = 8) lung was treated with either IRE or microwave ablation (MWA), followed by sacrifice at 2 and 28 days (four animals/timepoint) after treatment. En bloc samples of ablated lung were stained for blood vessels (CD31), ECM proteins (Collagen, Heparan sulfate, and Decorin), T cells (CD3), and macrophages (Iba1). Stained slides were analyzed with an image processing software (ImageJ) to count the number of positive staining cells or the percentage area of tissue staining for ECM markers, and the statistical difference was evaluated with Student's t-test. Results: Approximately 50% of the blood vessels and collagen typically seen in healthy lung were evident in IRE treated samples at Day 2, with complete destruction within MWA treated lung. These levels increased threefold by Day 28, indicative of post-IRE tissue remodeling and regeneration. Decorin and Heparan sulfate levels were reduced, and it remained so through the duration of observation. Concurrently, numbers of CD3⁺ T cells and macrophages were not different from healthy lung at Day 2 after IRE, subsequently increasing by 2.5 and 1.5-fold by Day 28. Similar findings were restricted to the peripheral inflammatory rim of MWA samples, wherein the central necrotic regions remained acellular through Day 28. Conclusion: Acute preservation of blood vessels and major ECM components was observed in IRE treated lung at acute time points, and it was associated with the increased infiltration and presence of T cells and macrophages, features that were spatially restricted in MWA treated lung.

Complications of renal interventions: a pictorial review of CT findings

A number of potential vascular and non-vascular complications can arise from surgical, extracorporeal shock wave lithotripsy, radiotherapy and radiological renal interventions, including percutaneous image-guided biopsy and drainage. Computed tomography scan is usually one of the first and most important diagnostic imaging examinations requested when a potential complication is suspected. There are a wide range of common and uncommon potential complications from renal interventions. An understanding of underlying risk factors is important to reduce potential complications from renal intervention. Radiologists play a crucial role in recognising and diagnosing post-renal intervention complications on computed tomography scans, which could significantly improve the patient’s prognosis.

Evaluation of Temperature Distribution Around the Probe in Cryoablation of Lipiodol-Mixed-Tissue Phantom

PURPOSE

To determine whether lipiodol, which has low thermal conductivity, influences ice ball formation during cryoablation of a lipiodol-mixed-tissue phantom.

MATERIALS AND METHODS

Lipiodol-mixed-tissue phantoms were created by injecting lipiodol (4-6 ml) into the renal arteries of ex vivo porcine kidneys (lipiodol group). A cryoprobe (CryoHit^™ Needle S) with a holder that was set with thermocouples at various positions around the cryoprobe was inserted. After freezing for 300 s, the followings were evaluated: ice ball size on CT, temperature distribution around the cryoprobe, and calculated distances at 0 °C and - 20 °C. Each variable was compared between lipiodol group (n = 6) those obtained in a control group without lipiodol injection (n = 6).

RESULTS

Mean ice ball diameter (width/length) on CT was 22.1 ± 2.3/22.9 ± 2.3 mm in the lipiodol group and 21.6 ± 0.7/22.2 ± 1.3 mm in the control group. Mean cryoprobe temperature was - 118 ± 3.0 °C in the lipiodol group and - 117 ± 2.6 °C in the control group. In both groups, temperature at the 3 mm thermocouple reached approximately - 50 °C and was < 0 °C within ~ 10 mm of the cryoprobe. Temperature of 0/- 20 °C occurred at a mean distance from the cryoprobe of 11.1 ± 0.5/6.9 ± 0.4 mm in the lipiodol group and 11.0 ± 0.2/6.9 ± 0.2 mm in the control group. There was no significant difference in any variable between the groups.

CONCLUSION

The inclusion of lipiodol in a tissue phantom had no negative effects on ice ball formation that were related to thermal conductivity.

Renal mass cryoablation: Melting time analysis of radiographic ice-ball after 5-minute active thawing by using serial ultrasound

OBJECTIVE

Cryoneedles removal before sufficient thawing may lead to tissue damage and bleeding. We analyzed melting time of radiographic ice-ball in renal percutaneous cryoablation (PCA) using ultrasound.

MATERIALS AND METHODS

Consecutive 27 patients who underwent PCA using cryoneedles of 2-4 for the renal mass (median size, 1.9 cm; range, 1.1-4.1 cm) were evaluated. Reconstructed CT images obtained during freezing were used to measure radiographic ice-ball volume. After completing final freezing, 5-min active thawing and following passive thawing were performed. Melting time of radiographic ice-ball during the thawing was analyzed by serial ultrasound examination. Melting time was defined as the time of complete disappearance of intrarenal posterior acoustic shadowing generated by radiographic ice-ball, which was analyzed by two independent radiologists. The relationship between total melting time and radiographic ice-ball volume was also analyzed by Spearman's rank correlation.

RESULTS

Median radiographic ice-ball volume was 30.5 cm³ (range, 26.6-37.3 cm³). After 5-min active thawing, radiographic ice-ball needed additional passive thawing of median 8-min or 9-min for complete melting in analyses of two independent radiologists, respectively (p > 0.05). The range of total melting time during active and passive thawing was 9-min-to-15-min for both radiologists, respectively. A positive correlation was found between total melting time and radiographic ice-ball volume (Spearman's rho, 0.644 and 0.479 for radiologist 1 and 2).

CONCLUSION

In our PCA protocol, radiographic ice-ball needed approximately 10-min passive thawing after 5-min active thawing for complete melting. This may help determine safe removal time of cryoneedles.

Percutaneous CT- and MRI-guided Cryoablation of cT1 Renal Cell Carcinoma: Intermediate- to Long-term Outcomes in 307 Patients

Background Percutaneous ablation for cT1 renal cell carcinoma (RCC) remains underused, partially because of heterogeneous and limited long-term outcomes data assessing recent cryoablation methods. Purpose To report intermediate- to long-term outcomes of image-guided percutaneous cryoablation of cT1 RCC and to compare outcomes for CT versus MRI guidance. Materials and Methods This HIPAA-compliant retrospective single-institution study assessed patients who underwent percutaneous cryoablation for solitary pathology-proven cT1 RCC between August 2000 and July 2017. Tumors (cT1a, n = 282; cT1b, n = 25; size range, 0.6-6.5 cm; median size, 2.5 cm) underwent cryoablation with CT (n = 155) or MRI (n = 152) guidance. Primary end points of overall survival (OS), disease-specific survival (DSS), imaging-confirmed disease-free survival (DFS), and local progression-free survival (LPFS) were calculated by using Kaplan-Meier analysis. Secondary end points of technique efficacy and adverse event rate were also calculated. Primary and secondary end points for CT and MRI guidance were compared by using univariable regression analysis. Results A total of 307 patients (mean age, 68 years ± 11 [standard deviation]; 192 men) were evaluated. Median clinical follow-up lasted 95 months (range, 8-219 months), and median imaging follow-up lasted 41 months (range, 0-189 months). Survival metrics at 3, 5, 10, and 15 years, respectively, included OS of 91% (95% confidence interval [CI]: 88%, 94%), 86% (95% CI: 82%, 90%), 78% (95% CI: 73%, 84%), and 76% (95% CI: 69%, 83%); DSS of 99.6% (95% CI: 99%, 100%), 99% (95% CI: 98%, 100%), 99% (95% CI: 98%, 100%), and 99% (95% CI: 98%, 100%); DFS of 94% (95% CI: 92%, 97%), 91% (95% CI: 88%, 96%), 88% (95% CI: 83%, 93%), and 88% (95% CI: 83%, 93%); and LPFS of 97% (95% CI: 94%, 99%), 95% (95% CI: 93%, 98%), 95% (95% CI: 93%, 98%), and 95% (95% CI: 93%, 98%). Survival did not significantly differ between CT and MRI guidance, with univariable Cox regression analysis hazard ratios of 0.97 (95% CI: 0.57, 1.67; P = .92) for OS, 0.63 (95% CI: 0.26, 1.52; P = .30) for DFS, and 0.83 (95% CI: 0.26, 2.74; P = .77) for LPFS. Primary and secondary technique efficacy were 96% and 99%, respectively. Overall adverse event rate was 14% (43 of 307), including 11 grade 3 events and three grade 4 events according to the Common Terminology Criteria for Adverse Events. Conclusion Percutaneous CT- and MRI-guided cryoablation of cT1 renal cell carcinoma had similar excellent intermediate- and long-term outcomes. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Georgiades in this issue.

Percutaneous Renal Ablation

Incidental small renal cell cancers are increasingly being diagnosed on cross-sectional imaging. This review article describes the indications for percutaneous ablation of small renal cell cancers, choice of ablation technologies and imaging follow-up.

Percutaneous ablation techniques for renal cell carcinoma: current status and future trends

Percutaneous ablation is an increasingly applied technique for the treatment of localized renal tumors, especially for elderly or co-morbid patients, where co-morbidities increase the risk of traditional nephrectomy. Ablative techniques are technically suited for the treatment of tumors generally not exceeding 4 cm, which has been set as general consensus cutoff and is described as the upper threshold of T1a kidney tumors. This threshold cutoff is being challenged, but with still limited evidence. Percutaneous ablation techniques for the treatment of renal cell carcinoma (RCC) include radiofrequency ablation, cryoablation, laser or microwave ablation; the main advantage of all these techniques over surgery is less invasiveness, lower complication rates and better patient tolerability. Currently, international guidelines recommend percutaneous ablation either as intervention for frail patients or as a first line tool, provided that the tumor can be radically ablated. The purpose of this article is to describe the basic concepts of percutaneous ablation in the treatment of RCC. Controversies concerning techniques and products and the need for patient-centered tailored approaches during selection among the different techniques available will be discussed.

Bowel injury complicating percutaneous cryoablation of large renal cell carcinoma

We report the case of a bowel injury, which occurred after the percutaneous cryoablation (PCA) of large renal cell carcinoma (RCC). A 50-year-old man with RCC measuring 47 mm in diameter. First, we performed transarterial embolization for the tumor, followed by PCA with hydrodissection, which displaced the small intestine from the iceball. The procedure was completed without any complication on the procedural day; however, the patient complained of appetite loss and abdominal pain 2 days after PCA. Computed tomography revealed a bowel injury at the small intestine adjacent to the tumor. After 7 days, ileus tube insertion, and fasting, the patient recovered from the bowel injury and was discharged 10 days after PCA. He underwent a second PCA because of a small recurrent renal tumor 5 months after the first PCA without complications. This case indicated that a bowel injury after PCA for RCC could be treated conservatively.

Percutaneous Image-guided Thermal Ablation for Renal Cell Carcinoma

Nephrectomy is the gold standard for the treatment of renal cell carcinoma (RCC). However, some patients are not suitable candidates for nephrectomy because of high surgical risk, reduced renal function, or the presence of multiple renal tumors. Percutaneous image-guided thermal ablation, including cryoablation and radiofrequency ablation, is a minimally invasive and highly effective treatment and can be used to treat RCC in patients who are not good candidates for surgery. This article will review percutaneous image-guided thermal ablation for RCC, covering treatment indications, ablation modalities and techniques, oncologic outcomes, and possible complications. In addition, the characteristics of each ablation modality and its comparison with nephrectomy are also presented.

Imaging of Small Renal Masses before and after Thermal Ablation

Thermal ablation of small renal masses is increasingly accepted as an alternative to partial nephrectomy, particularly in patients with multiple comorbidities. Many professional societies support this alternate treatment with updated guidelines. Before performing thermal ablation, it is important to stratify risk and assess technical feasibility by evaluating tumor imaging features such as size, location, and centrality. Routine postablation imaging with CT or MRI is necessary for assessment of residual or recurrent tumor, evidence of complications, or new renal masses outside the ablation zone. The normal spectrum and evolution of findings at CT and MRI include a halo appearance of the ablation zone, ablation zone contraction, and ablation zone calcifications. Tumor recurrence frequently manifests at CT or MRI as new nodular enhancement at the periphery of an expanding ablation zone, although it is normal for the ablation zone to enlarge within the first few months. Recognizing early tumor recurrence is important, as small renal masses are often easily treated with repeat ablations. Potential complications of thermal ablation include vascular injury, urine leak, ureteral stricture, nerve injury, and bowel perforation. The risk of these complications may be related to tumor size and location.^©RSNA, 2019.

Percutaneous cryoablation for renal cell carcinoma using ultrasound-guided targeting and computed tomography-guided ice-ball monitoring: radiation dose and short-term outcomes

BACKGROUND

Usefulness of ultrasound (US)-guided mass targeting and computed tomography (CT)-guided ice-ball monitoring in percutaneous cryoablation (PCA) for renal cell carcinoma (RCC) is still uncertain.

PURPOSE

To assess radiation dose and short-term outcomes of PCA for RCC using US-guided targeting and CT-guided ice-ball monitoring.

MATERIAL AND METHODS

Thirty-nine consecutive patients who underwent PCA for biopsy-proven RCC were included. Mass targeting was performed with US and ice-ball was monitored with CT guidance. Effective radiation dose of CT during PCA was recorded. Follow-up was conducted with contrast-enhanced CT or magnetic resonance imaging (MRI) (mean follow-up time = 10.1 ± 7.0 months). Local tumor progression was defined by the presence of focal enhancing areas at the ablation zone (CT, ≥ 20 HU; MRI, presence of focal enhancement on subtraction contrast-enhanced image). Technical success, major complication rate (e.g. Clavien-Dindo classification ≥ 3), and one-year local tumor progression-free survival (PFS) rate were analyzed.

RESULTS

Mean effective radiation dose in association with PCA was 12.1 ± 4.5 mSv (range = 7.0-25.2 mSv). Technical success was achieved in 100%. Local tumor progression occurred in a single patient (2.6%, 1/39), and one-year local tumor PFS rate was 95.7%. No major complication was found.

CONCLUSION

PCA using US-guided targeting and CT-guided ice-ball monitoring may allow acceptable local tumor control for RCC, as a radiation-reducing strategy.

The Role of Ablation and Minimally Invasive Techniques in the Management of Small Renal Masses

CONTEXT

Nephron-sparing approaches are increasingly recommended for incidental small renal masses. Herein, we review the current literature regarding the safety and efficacy of focal therapy, including percutaneous ablation, for small renal masses.

OBJECTIVE

To summarize the application of ablative therapy in the management of small renal masses.

EVIDENCE ACQUISITION

PubMed and Medline database search was performed to look for findings published since 2000 on focal therapy for small renal masses. After literature review, 64 articles were selected and discussed.

EVIDENCE SYNTHESIS

Radiofrequency ablation and cryotherapy are the most widely used procedures with intermediate-term oncological outcome comparable with surgical series. Cost effectiveness seems excellent and side effects appear acceptable. To date, no randomized trial comparing percutaneous focal therapy with standard surgical approach or active surveillance has been performed.

CONCLUSIONS

Focal ablative therapies are now accepted as effective treatment for small renal tumors. For tumors <3cm, oncological effectiveness of ablative therapies is comparable with that of partial nephrectomy. Percutaneous ablation has fewer complications and a better postoperative profile when compared with minimally invasive partial nephrectomy.

PATIENT SUMMARY

Focal ablative therapies are now accepted as effective treatment for small renal tumors. For tumors <3cm, oncological effectiveness of ablative therapies is comparable with that of partial nephrectomy.

[Percutaneous renal ablation: Pre-, per-, post-interventional evaluation modalities and adapted management]

OBJECTIVES

Ablative treatment (AT) rise is foreseen, validation of steps to insure good proceedings is needed. By looking over the process of the patient, this study evaluates the requirements and choices needed in every step of the management.

METHODS

We searched MEDLINE^®, Embase^®, using (MeSH) words and we looked for all the studies. Investigators graded the strength of evidence in terms of methodology, language and relevance.

RESULTS

Explanations of AT proposal rather than partial nephrectomy or surveillance have to be discussed in a consultation shared by urologist and interventional radiologist. Per-procedure choices depend on predictable ballistic difficulties. High volume, proximity of the hilum or of a risky organ are in favor of general anesthesia, cryotherapy and computed tomography/magnetic resonance imaging (CT/MRI). Percutaneous approach should be privileged, as it seems as effective as the laparoscopic approach. Early and delayed complications have to be treated both by urologist and radiologist. Surveillance by CT/MRI insure of the lack of contrast-enhanced in the treated area. Patients and tumors criteria, in case of incomplete treatment or recurrence, are the key of the appropriate treatment: surgery, second session of AT, surveillance.

CONCLUSION

AT treatments require patient's comprehension, excellent coordination of the partnership between urologist and radiologist and relevant choices during intervention.

Decision Making: Thermal Ablation Options for Small Renal Masses

Renal cell carcinoma is a relatively common tumor, with an estimated 63,000 new cases being diagnosed in the United States in 2016. Surgery, be it with partial or total nephrectomy, is considered the mainstay of treatment for many patients. However, those patients with small renal masses, typically less than 3 to 4 cm in size who are deemed unsuitable for surgery, may be suitable for percutaneous thermal ablation. We review the various treatment modalities, including radiofrequency ablation, microwave ablation, and cryoablation; discuss the advantages and disadvantages of each method; and review the latest data concerning the performance of the various ablative modalities compared with each other, and compared with surgery.

Tips and tricks for a safe and effective image-guided percutaneous renal tumour ablation

Abstract

Image-guide thermal ablations are nowadays increasingly used to provide a minimally invasive treatment to patients with renal tumours, with reported good clinical results and low complications rate. Different ablative techniques can be applied, each with some advantages and disadvantages according to the clinical situation. Moreover, percutaneous ablation of renal tumours might be complex in cases where there is limited access for image guidance or a close proximity to critical structures, which can be unintentionally injured during treatment. In the present paper we offer an overview of the most commonly used ablative techniques and of the most important manoeuvres that can be applied to enhance the safety and effectiveness of percutaneous image-guided renal ablation. Emphasis is given to the different technical aspects of cryoablation, radiofrequency ablation, and microwave ablation, on the ideal operating room setting, optimal image guidance, application of fusion imaging and virtual navigation, and contrast enhanced ultrasound in the guidance and monitoring of the procedure. Moreover, a series of protective manoeuvre that can be used to avoid damage to surrounding sensitive structures is presented. A selection of cases of image-guided thermal ablation of renal tumours in which the discussed technique were used is presented and illustrated.

Teaching points

• Cryoablation, radiofrequency and microwave ablation have different advantages and disadvantages.

• US, CT, fusion imaging, and CEUS increase an effective image-guidance.

• Different patient positioning and external compression may increase procedure feasibility.

• Hydrodissection and gas insufflation are useful to displace surrounding critical structures.

• Cold pyeloperfusion can reduce the thermal damage to the collecting system.

In vivo irreversible electroporation kidney ablation: experimentally correlated numerical models

Irreversible electroporation (IRE) ablation uses brief electric pulses to kill a volume of tissue without damaging the structures contraindicated for surgical resection or thermal ablation, including blood vessels and ureters. IRE offers a targeted nephron-sparing approach for treating kidney tumors, but the relevant organ-specific electrical properties and cellular susceptibility to IRE electric pulses remain to be characterized. Here, a pulse protocol of 100 electric pulses, each 100 μs long, is delivered at 1 pulse/s to canine kidneys at three different voltage-to-distance ratios while measuring intrapulse current, completed 6 h before humane euthanasia. Numerical models were correlated with lesions and electrical measurements to determine electrical conductivity behavior and lethal electric field threshold. Three methods for modeling tissue response to the pulses were investigated (static, linear dynamic, and asymmetrical sigmoid dynamic), where the asymmetrical sigmoid dynamic conductivity function most accurately and precisely matched lesion dimensions, with a lethal electric field threshold of 575 ± 67 V/cm for the protocols used. The linear dynamic model also attains accurate predictions with a simpler function. These findings can aid renal IRE treatment planning under varying electrode geometries and pulse strengths. Histology showed a wholly necrotic core lesion at the highest electric fields, surrounded by a transitional perimeter of differential tissue viability dependent on renal structure.

The feasibility of percutaneous renal cryoablation under local anaesthesia

OBJECTIVES

The aim of this study was to evaluate the feasibility of cryoablation of renal tumours without sedation.

MATERIALS AND METHODS

We prospectively evaluated 149 computed tomography-guided renal cryoablation procedures that were performed at our institution between 2009 and 2013. The patients received only 1 g of IV paracetamol prior to the procedure; intraprocedural, local anaesthesia was administered. We recorded the date and duration of the procedure, size and location of the tumour, number of cryoneedles used, need for dissection with saline or carbon dioxide and intraprocedural degree of pain, which was scored using an established visual analogue pain score (VAS) (0-10). Multivariate analysis was used to identify the associations between the recorded parameters and VAS.

RESULTS

An interventional radiologist and a technician could perform all procedures without the help of anaesthesiologists and with adequate analgesia. The pain level ranged from 0 to 8 (mean, 2.0). It did not correlate with the tumour size or with the number of cryoneedles. It was significantly greater when the ice ball involved renal cavities (p = .0033) and when carbon dioxide was used for dissection (p < .0001). Conversely, the team experience was positively correlated with lower pain levels (p = .0381).

CONCLUSION

This study demonstrates that the cryoablation of renal tumours is feasible by interventional radiologists alone using a combination of IV paracetamol and local anaesthesia.

Renal ablation update

Thermal ablative technologies have evolved considerably in the recent past and are now an important component of current clinical guidelines for the treatment of small renal masses. Both radiofrequency ablation and cryoablation have intermediate-term oncologic control that rivals surgical options, with favorable complication profiles. Studies comparing cryoablation and radiofrequency ablation show no significant difference in oncologic control or complication profile between the two modalities. Early data from small series with microwave ablation have shown similar promising results. Newer technologies including irreversible electroporation and high-intensity-focused ultrasound have theoretical advantages, but will require further research before becoming a routine part of the ablation armamentarium. The purpose of this review article is to discuss the current ablative technologies available, briefly review their mechanisms of action, discuss technical aspects of each, and provide current data supporting their use.

Percutaneous ablation of the small renal mass-techniques and outcomes

An increasing number of T1a renal cell carcinomas are being diagnosed in recent years, in part due to incidental detection from the increased use of cross-sectional imaging. Although partial nephrectomy is still considered the primary treatment for these small renal masses, percutaneous ablation is now being performed as a standard therapeutic, nephron-sparing approach in patients who are poor surgical candidates. Clinical studies to date have demonstrated that percutaneous ablation is an effective therapy with acceptable outcomes and low risk in the appropriate clinical settings. This article will review various clinical aspects regarding the percutaneous ablation of small renal masses, including patient selection, preprocedural preparations, and the procedural considerations of commonly employed ablative technologies. Specific techniques such as radiofrequency ablation, cryoablation, microwave ablation, irreversible electroporation, and high-intensity focused ultrasound will be addressed in detail. In addition, the technical and oncologic outcomes of percutaneous ablation will be discussed and referenced to that of partial nephrectomy.

Indications for renal fine needle aspiration biopsy in the era of modern imaging modalities

Background:

Renal fine needle aspiration biopsy (FNAB) has become an uncommon procedure in the era of renal helical computed tomography (CT), which has high diagnostic accuracy in the characterization of renal cortical lesions. This study investigates the current indications for renal FNAB. Having knowledge of the specific clinico-radiologic scenario that led to the FNAB, cytopathologists are better equipped to expand or narrow down their differential diagnosis.

Materials and Methods:

All renal FNABs performed during a 6 year interval were retrieved. Indication for the procedure was determined from the clinical notes and radiology reports.

Results:

Forty six renal FNABs were retrieved from 43 patients (14 females and 29 males with a mean age of 52 years [range, 4-81 years]). Twenty one cases (45.6%) were performed under CT-guidance and 25 cases (54.4%) under US-guidance. There were four distinct indications for renal FNAB: (1) solid renal masses with atypical radiological features or poorly characterized on imaging studies due to lack of intravenous contrast or body habitus (30.2%); (2) confirmation of radiologically suspected renal cell carcinoma in inoperable patients (advanced stage disease or poor surgical candidate status) (27.9%); (3) kidney mass in a patient with a prior history of other malignancy (27.9%); and (4) miscellaneous (drainage of abscess, indeterminate cystic lesion, urothelial carcinoma) (14.0%). 36 patients (83.7%) received a specific diagnosis based on renal FNAB cytology.

Conclusions:

Currently, renal fine needle aspiration remains a useful diagnostic tool in selected clinico-radiologic scenarios.

Ten-year experience of percutaneous image-guided radiofrequency ablation of malignant renal tumours in high-risk patients

OBJECTIVES

To evaluate survival and outcomes after percutaneous radiofrequency ablation (RFA) of malignant renal tumours in high-risk patients with long-term follow-up.

METHODS

Between 2002 and 2009, 62 patients (71 tumours), with a median age of 73.5 years (20-87), consecutively treated with RFA under ultrasound or computed tomography guidance for malignant renal tumours were retrospectively selected and prospectively followed until 2012, including 25 patients (40.3 %) with solitary kidney and 7 cystic cancers. Maximal tumour diameters were between 8 and 46 mm (median: 23 mm).

RESULTS

Radiofrequency ablation was technically possible for all patients. Mean follow-up was 38.8 months (range: 18-78 months). Primary and secondary technique effectiveness was 95.2 % and 98.4 % per patient respectively. The rates of local tumour progression and metastatic evolution were 3.2 % and 9.7 % per patient and were associated with tumour size >4 cm (P = 0.005). The disease-free survival rates were 88.3 % and 61.9 % at 3 and 5 years. No significant difference in glomerular filtration rates before and after the procedure was observed (P = 0.107). The major complications rate was 5.9 % per session with an increased risk in the case of central locations (P = 0.006).

CONCLUSIONS

Percutaneous renal RFA appears to be safe and effective with useful nephron-sparing results.

KEY POINTS

• Radiofrequency ablation (RFA) is a well-tolerated technique according to mid-term results. • RFA for malignant renal tumours preserved renal function in high-risk patients. • Mid-term efficacy of RFA was close to that of formal conservative surgery. • Tumour size and central location limit the efficacy and safety of RFA.

Successful conservative management of a colorenal fistula complicating percutaneous cryoablation of renal tumors: a case report

Introduction

Colorenal fistula is a rare phenomenon and may complicate percutaneous cryoablation of renal cell carcinoma. Treatment remains controversial.

Case presentation

A 62-year-old Caucasian man presented with pneumaturia and left flank pain six weeks following ultrasound-guided percutaneous cryoablation of two recurrent lesions in the left kidney 14 years after partial left nephrectomy for a left renal cell carcinoma. A computed tomography scan eight weeks after cryoablation revealed a cryoablated mass with adjacent stranding and adherent descending colon as well as bubbles of gas in the area of stranding, the left collecting system, and the bladder. These features were consistent with a colorenal fistula at the site of previous ablation. Successful resolution of the fistula, both clinical and radiological, was achieved following a complete conservative non-interventional out-patient approach. No ureteric stent or surgical intervention was employed.

Conclusions

In the absence of severe symptoms or sepsis, complete conservative management of a colorenal fistula complicating percutaneous cryoablation of renal tumors should be considered prior to interventional stenting or resectional surgery.

An overview of image-guided percutaneous ablation of renal tumors

Although nephron-sparing surgery remains the gold standard treatment for small renal tumors, minimally invasive image-guided percutaneous ablation is becoming a viable alternative to operative resection. Percutaneous radiofrequency ablation (RFA) and cryoablation show high technical success rates, a relatively low incidence of residual or recurrent tumor, and competitive rates of patient survival. In this review, an overview of the current status of image-guided percutaneous ablation of renal tumors is presented, with a focus on procedure indications and patient selection, technical aspects of ablation procedures, and treatment outcomes and patient follow-up.

[Abscesso-colonic fistula following radiofrequency ablation therapy for hepatocellular carcinoma; a case successfully treated with histoacryl embolization]

Hepatocellular carcinoma (HCC) is one of the most common malignant neoplasms occuring worldwide. Although surgical resection still remains the treatment of choice for HCC, radiofrequency ablation (RFA) has emerged as reliable alternatives to resection. It is less invasive and can be repeated after short intervals for sequential ablation in case of multiple lesions. The most common complication of RFA is liver abscess, and bile duct injury such as bile duct stricture has been reported. This is a case report of a rare complication of abscesso-colonic fistula after RFA for HCC. The case was treated by percutaneous abscess drainage and antibiotics and occlusion of abscesso-colonic fistula with n-butyl-2-cyanoacrylate embolization.

Imaging in renal cell carcinoma

Imaging plays a central role in the detection, diagnosis, staging, and follow-up of renal cell carcinoma (RCC). Most renal masses are incidentally detected with modern, high-resolution imaging techniques and a variety of management options exist for the renal masses encountered today. This article discusses the role of multiple imaging modalities in the diagnosis of RCC and the imaging features of specific pathologic subtypes and staging techniques. Future directions in RCC imaging are presented, including dynamic contrast-enhanced and unenhanced techniques, as well as the development of novel tracers for positron emission tomography.

Percutaneous cryoablation of renal lesions with radiographic ice ball involvement of the renal sinus: analysis of hemorrhagic and collecting system complications

OBJECTIVE

The purpose of this study was to determine the incidence of collecting system and hemorrhagic complications resulting from CT-guided percutaneous cryoablation of renal tumors in which the radiographic ice ball abuts or involves the renal sinus.

MATERIALS AND METHODS

From November 2005 through July 2009 at our institution, we performed 129 CT-guided percutaneous cryoablation procedures on 107 patients (mean age, 64 years) with renal masses suspicious of being renal cell carcinoma. Radiographic ice balls that abutted or overlapped the renal sinus were classified as central; the other lesions were classified as noncentral. Medical records and follow-up images were retrospectively reviewed for hemorrhage requiring intervention and for evidence of collecting system injury. The mean follow-up period was 9.3 months.

RESULTS

The radiographic ice ball was classified as central in 67 cases. In these central ablations, the mean sinus involvement was 6.2 mm (range, 0-19 mm), 41 ice balls overlapping the renal sinus by 6 mm or more (mean, 9.4 mm). No cases of collecting system injury were identified for any ablation. Overall, there was only one hemorrhagic complication requiring intervention, and it occurred in a noncentral ablation.

CONCLUSION

CT-guided percutaneous cryoablation of renal masses with ice ball overlap of the renal sinus resulted in no cases of collecting system injury or serious hemorrhagic complications in our series.

Percutaneous cryoablation of anterior renal masses: technique, efficacy, and safety

OBJECTIVE

The safety and efficacy of renal tumor ablation are related, in part, to tumor location. Anterior tumors present a challenge due to the risk of injury to adjacent structures. The purpose of this study was to review the techniques, complications, and short-term outcomes of percutaneous cryoablation of anterior renal masses at a single institution.

MATERIALS AND METHODS

We retrospectively identified the cases of 35 patients with 38 anterior renal masses managed with percutaneous imaging-guided cryoablation of renal tumors from March 2003 through February 2009. The technical success of the ablation procedure, serious complications, and evidence of local tumor recurrence were evaluated for each patient.

RESULTS

The average maximal diameter of the anterior renal masses was 2.9 cm (SD, 0.9 cm; range, 1.4-4.8 cm). A single cryoablation procedure was performed for treatment of each patient, and technically successful ablation was achieved for all 38 tumors. A single severe adverse event occurred in one of the 35 patients (3% major complication rate). This patient had a pulmonary embolism (diagnosed at CT angiography the day after ablation). He recovered and was discharged from the hospital with anticoagulant medication only 2 days after the procedure. No local tumor recurrence was identified in any of the 29 patients who underwent follow-up contrast-enhanced CT or MRI with images available for review 3 months or longer from the time of ablation (mean, 18 months; range, 3-45 months).

CONCLUSION

Percutaneous cryoablation of anterior renal masses can be performed with high technical success and low complication rates. The lack of local renal tumor recurrence at short-term follow-up evaluation in this study is encouraging, but long-term follow-up is necessary to ensure the durability of treatment.

Cryoablation vs. radiofrequency ablation for small renal masses

RATIONALE AND OBJECTIVES

Cancer of the kidney is the third most common cancer of the urinary tract, and renal cell carcinoma is the most lethal of all genitourinary tumors. The incidental discovery of renal cell carcinoma has increased with increased use of cross-sectional imaging. Concomitantly, minimally invasive ablative technologies, including image-guided cryoablation, radiofrequency ablation, and others, have evolved as therapeutic options for small renal masses.

MATERIALS AND METHODS

Between 2006 and 2009, 111 patients (age range, 31-91 years; mean age, 70 years) underwent percutaneous computed tomography-guided thermal ablation for suspected renal cell carcinoma at two major academic centers. Outcomes data were retrospectively collected and analyzed to compare recurrence rates for patients undergoing radiofrequency ablation (n = 41) versus cryoablation (n = 70).

RESULTS

There were four cases of suspicious enhancement on follow-up computed tomography or magnetic resonance imaging in each group, with cumulative imaging recurrence rates of 11% and 7% for radiofrequency ablation and cryoablation, respectively. Log rank test analysis revealed no significant difference between rates of imaging recurrence between the two groups (P = .6044).

CONCLUSIONS

These results suggest that the use of cryoablative technology will result in similar outcomes compared with radiofrequency ablation.

Effectiveness of ultrasound-guided radiofrequency ablation in the treatment of 36 renal cell carcinoma tumours compared with published results of using computed tomography guidance

This study aimed to analyse the outcomes of ultrasound (US) guided radiofrequency ablation (RFA) in patients with renal lesions and to compare our outcomes with published results of ablations carried out when using computed tomography (CT) guidance. This retrospective study evaluated RFA of 36 renal tumours in 32 patients (M = 21, F = 11). The mean patient age was 70 years (range, 39-89 years). Ablations were performed by using either multi-tined applicators or cooled and/or cluster applicators under US guidance. Applicator size varied from 2-5 cm, depending on the size of the index tumour. Conscious sedation was administered by an anesthetist. Follow-up imaging by using contrast-enhanced CT was performed 1, 3, 6, and 12 months after RFA, and yearly thereafter. The mean tumour follow-up time was 12 months (range, 1-35 months). The mean tumour size was 2.7 cm (range, 1-5 cm). Primary effectiveness was achieved in 31 cases (86.1%), with patients in 5 cases (11.1%) demonstrating residual disease. Three patients had repeated sessions, which were technically successful. The remaining 2 patients were not re-treated because of patient comorbidities. As a result, secondary effectiveness was achieved in 34 patients (94.4%). In 1 patient, a new lesion developed in the same kidney but remote from the 2 prior areas of treatment. Hydrodissection was performed in 3 patients (8.3%), manipulation or electrode repositioning in 11 patients (30.6%), and ureteric cooling in 1 patient (2.8%). Minor and major complications occurred in 3 (8.3%) and 3 (8.3%) patients, respectively. Correlation coefficients were calculated for distance from skin to tumour and risk of complication as well as compared with primary and secondary effectiveness. This study demonstrates that US-guided RFA is an effective treatment for renal lesions, with rates of effectiveness and complication rates comparable with published CT-guided RFA results.

Percutaneous vs surgical cryoablation of the small renal mass: is efficacy compromised?

OBJECTIVE

• To review and analyse the cumulative literature to compare surgical and percutaneous cryoablation of small renal masses (SRMs).

METHODS

• A MEDLINE search was performed (1966 to February 2010) of the published literature in which cryoablation was used as therapy for localized renal masses. • Residual disease was defined as persistent enhancement on the first post-ablation imaging study, while recurrent disease was defined as enhancement after an initially negative postoperative imaging study, consistent with the consensus definition by the Working Group on Image-Guided Tumor Ablation. • Data were collated and analysed using the two-sample Mann-Whitney test and random-effects Poisson regression, where appropriate.

RESULTS

• In all, 42 studies, representing 1447 lesions treated by surgical (n= 28) or percutaneous (n= 14) cryoablation were pooled and analysed. • No significant differences were detected between approaches regarding patient age (median 67 vs 66 years, P= 0.55), tumour size (median 2.6 vs 2.7 cm, P= 0.24),or duration of follow-up (median 14.9 vs 13.3 months, P= 0.40). • Differences in rates of unknown pathology also failed to reach statistical significance (14 vs 21%, P= 0.76). The difference in the rate of residual tumour was not statistically different (0.033 vs 0.046, P= 0.25), nor was the rate of recurrent tumour (0.008 vs 0.009, P= 0.44). • The reported rate of metastases was negligible in both groups, precluding statistical analysis.

CONCLUSIONS

• Cryoablation has shown acceptable short-term oncological results as a viable strategy for SRMs. • Analysis of the cumulative literature to date shows that surgical and percutaneous cryoablation have similar oncological outcomes.

Percutaneous cryoablation of renal masses >or=3 cm: efficacy and safety in treatment of 108 patients

PURPOSE

To evaluate our single institution experience with percutaneous cryoablation of renal masses >or=3 cm in diameter for complications and short-term outcomes.

PATIENTS AND METHODS

Between March 2003 and February 2009, 108 patients with 110 renal masses >or=3 cm in diameter were treated with percutaneous cryoablation therapy. Technical success of the ablation procedure, complications, and evidence for local tumor recurrence were evaluated for each patient.

RESULTS

Average maximal renal tumor diameter was 4.1 cm (range 3.0-8.3 cm; standard deviation 1.1 cm). A single cryoablation procedure was performed for treatment of each patient. A technically successful ablation was achieved for 107 of 110 (97%) tumors. The three technical failures all resulted from incomplete cryoablation of the deepest margin of a centrally located renal tumor. A total of 9 severe adverse events occurred in six patients, resulting in an 8% major complication rate. Two patients in whom major complications developed were part of the group of only four patients for whom ablation was performed for tumors > 7 cm in diameter. There were no procedural-related deaths. No evidence for local tumor recurrence was identified in any patients with follow-up contrast-enhanced CT or MRI obtained 3 months or longer from the time of the ablation. Follow-up in these patients averaged 15 months (range 3-42 mos).

CONCLUSION

Percutaneous cryoablation of renal masses >or=3 cm in diameter can be performed with high technical success and low complication rates. Extra scrutiny is needed during cryoablation of central renal masses to make sure the ablation zone extends to include the deepest margin of the tumor. Although our experience is limited, percutaneous cryoablation of renal tumors > 7 cm in diameter may be associated with increased complications. The lack of local renal tumor recurrences seen in this study on short-term follow-up is encouraging, but long-term follow-up remains necessary to ensure treatment durability.

Long-term results after computed-tomography-guided percutaneous radiofrequency ablation for small renal tumors

PURPOSE

To present the long-term results and to identify possible risk factors for recurrence after radiofrequency ablation (RFA) for renal tumors.

PATIENTS AND METHODS

Thirty-one patients with a total of 39 renal tumors ranging from 1.3 to 7.5 cm (mean size 3.1 cm) were treated with RFA using a Rita Medical System model 1500 RF generator attached to a 15-gauge Starburst XL probe under percutaneous CT scan guidance. The average patient age was 61.4 years (range 37-86 y). Indications for RFA were bilateral tumors, presence of serious comorbidities, a high risk of development of additional renal-cell carcinomas, marginal renal function, and patient preference. No tumor was biopsied before treatment; therefore, only local control success rates could be provided. Recurrence was defined as enhancement or lesion enlargement on follow-up CT scan. Statistical analysis was performed to identify possible risk factors for recurrence. Parameters tested were age, sex, and number of ablation sessions, tumor size, location, multiplicity, body mass index, and American Society of Anesthesiologists score.

RESULTS

Initial ablation success rate was 90% and with repeated treatment, a success rate of complete ablation reached 97%. Average follow-up was 61.2 months (range 36-84 mos). Recurrence was seen in four tumors. The risk factor associated with recurrence was tumor size exceeding 4 cm (P < 0.01, relative risk [RR] = 3.31). Overall 3- and 5-year tumor control rate was 92% and 89%, respectively. Tumor size was also predictive for recurrence in the subgroup of 17 patients followed for more than 5 years (P = 0.02, RR = 3.15). Tumor control rate for this subgroup was 90%.

CONCLUSIONS

According to our results, larger tumor size was prognostic for recurrence after RFA for renal tumors. This treatment seems to demonstrate excellent tumor control long-term results, comparable to those achieved by nephron-sparing surgery in a selected group of patients.

Tumor ablation and nanotechnology

Next to surgical resection, tumor ablation is a commonly used intervention in the treatment of solid tumors. Tumor ablation methods include thermal therapies, photodynamic therapy, and reactive oxygen species (ROS) producing agents. Thermal therapies induce tumor cell death via thermal energy and include radiofrequency, microwave, high intensity focused ultrasound, and cryoablation. Photodynamic therapy and ROS producing agents cause increased oxidative stress in tumor cells leading to apoptosis. While these therapies are safe and viable alternatives when resection of malignancies is not feasible, they do have associated limitations that prevent their widespread use in clinical applications. To improve the efficacy of these treatments, nanoparticles are being studied in combination with nonsurgical ablation regimens. In addition to better thermal effect on tumor ablation, nanoparticles can deliver anticancer therapeutics that show a synergistic antitumor effect in the presence of heat and can also be imaged to achieve precision in therapy. Understanding the molecular mechanism of nanoparticle-mediated tumor ablation could further help engineer nanoparticles of appropriate composition and properties to synergize the ablation effect. This review aims to explore the various types of nonsurgical tumor ablation methods currently used in cancer treatment and potential improvements by nanotechnology applications.

Colo-renal fistula: An unusual cause of hematochezia

A 76 year old woman with bloody stools and symptomatic anemia presented to the Emergency Department approximately 2 wk after computed tomography (CT)-guided cryoablation to a 4.5 cm renal cell carcinoma on her left posterior kidney. The patient was initially prepped for a colonoscopy to view possible causes of lower gastrointestinal bleeding. However, the patient had a CT with PO contrast that revealed a variation of a renoalimentary fistula. The patient was subsequently brought to the operating room, and it was discovered that a colo-renal fistula had formed, with transmural perforation of the posterior descending colon. A left nephrectomy, left colectomy with colostomy and Hartmann’s pouch was performed.

Cryoablation: mechanism of action and devices

Cryoablation refers to all methods of destroying tissue by freezing. Cryoablation causes cellular damage, death, and necrosis of tissues by direct mechanisms, which cause cold-induced injury to cells, and indirect mechanisms, which cause changes to the cellular microenvironment and impair tissue viability. Cellular injury, both indirect and direct, can be influenced by four factors: cooling rate, target temperature, time at target temperature, and thawing rate. In this review, the authors describe the mechanisms of cellular injury that occur with cryoablation, the major advantages and disadvantages of cryoablation compared with other thermal ablation techniques, and the current commercially available cryoablation ablation systems.