Correlation between renal ablation zone in contrast-enhanced CT and non-enhanced MRI during the early period following percutaneous cryoablation

Propensity score-matched analysis comparing robot-assisted partial nephrectomy and image-guided percutaneous cryoablation for cT1 renal cell carcinoma

OBJECTIVES

This study aimed to compare the clinical outcomes of robot-assisted partial nephrectomy (RAPN) and image-guided percutaneous cryoablation (IG-PCA) for clinical T1 renal cell carcinoma.

MATERIALS AND METHODS

We conducted a retrospective analysis of 679 patients with clinical T1 renal cell carcinoma treated with RAPN or IG-PCA between 2012 and 2021. Propensity scores were calculated via logistic analysis to adjust for imbalances in baseline characteristics. We compared oncological and functional outcomes between the 2 treatment groups.

RESULTS

Following the matching process, 108 patients were included in each group. No patient in the RAPN group developed local recurrence. In the IG-PCA group, three patients experienced local tumor progression. The patients underwent salvage thermal ablations by the secondary technique; 2 underwent IG-PCA and 1 underwent microwave ablation, resulting in a local control rate of 100%. The Kaplan-Meier analysis showed no statistically significant differences between the groups in terms of 5-year recurrence-free survival, metastasis-free survival, and overall survival (log-rank test; P = 0.11, P = 0.64, and P = 0.17, respectively). No significant differences were observed in the 2 treatments in major and overall complication rates (P = 0.75 and P = 0.82, respectively). Both groups showed similar rates of less than 10% estimated glomerular filtration rate decline at 12 months post-treatment and 5-year renal function preservation rates (P = 0.88 and P = 0.38, respectively).

CONCLUSIONS

IG-PCA demonstrated oncological outcomes comparable to those of RAPN. RAPN addressed the disadvantages of conventional procedures and allowed for safety outcomes comparable to IG-PCA.

Unenhanced CT as an Alternative to Contrast-Enhanced CT in Evaluating Renal Cryoablation Zones

Background Advances in imaging technology and the increased use of abdominal imaging have led to a rise in renal cell carcinoma (RCC) detection. While surgery remains the primary treatment for small RCCs, minimally invasive procedures like cryoablation are gaining popularity, particularly for patients with comorbidities or renal dysfunction. CT-guided cryoablation offers advantages, including high spatial resolution and real-time visualization during the procedure. Post-procedure imaging is essential for assessing treatment success, with contrast-enhanced CT (CE-CT) typically considered vital. However, many patients, especially older individuals, have renal dysfunction that limits the use of contrast agents. In such cases, unenhanced CT (UE-CT) presents a viable alternative for post-procedural evaluation. This study explored the effectiveness of UE-CT in assessing cryoablation zones as a substitute for CE-CT. Materials and Methods This retrospective study included 54 patients (58 tumors) who underwent cryoablation at a single institution between 2014 and 2024. Only patients with available early follow-up CT (within three days post-cryoablation) and subsequent follow-up were included. Tumors marked with lipiodol prior to cryoablation and cases requiring transcatheter arterial embolization due to extravasation immediately after cryoablation were excluded. Percutaneous renal cryoablation was performed under CT fluoroscopy, and the ablation zone was assessed using a 64-channel multi-slice CT scanner. UE-CT was conducted before the procedure, followed by both UE-CT and CE-CT within three days after cryoablation. CT attenuation values were measured for pre-procedure UE-CT (kidneys and tumor), post-procedure UE-CT (kidneys, cryoablation zone, and tumor), and post-procedure CE-CT (kidneys, cryoablation zone, and tumor). Tumor volumes in the post-procedure regions were evaluated on both UE-CT and CE-CT. Statistical analyses were performed using Wilcoxon's signed-rank test and Spearman's rank correlation coefficient, with interobserver agreement determined by the intraclass correlation coefficient. Results The median tumor diameter was 1.56 cm (IQR: 1.33-2.00 cm). On UE-CT, the cryoablation zone exhibited high attenuation, while it showed low attenuation on CE-CT. The median attenuation values of the kidneys on UE-CT before and after cryoablation were not significantly different (33.6 Hounsfield unit (HU) vs. 34.3 HU, P = 0.17). However, on CE-CT, the median attenuation values of normal kidneys and the cryoablation zone significantly differed (171.7 HU vs. 55.7 HU, P < 0.0001). Similarly, on UE-CT, there was a significant difference in the median attenuation values between normal kidneys and the cryoablation zone (34.3 HU vs. 47.4 HU, P < 0.0001). The median renal volumes of the unenhanced regions on CE-CT and those with attenuation changes on UE-CT were not significantly different (26.52 cm³ vs. 28.83 cm³, P = 0.86). These values showed a strong correlation (r = 0.95; 95% CI: 0.91-0.97). Conclusions This study showed that UE-CT can reliably estimate the ablation zone in RCC patients post-cryoablation. While the contrast between the ablation zone and normal renal parenchyma was lower on UE-CT compared to CE-CT, the ablation zone was still detectable and highly correlated with CE-CT results. Further research with larger sample sizes is needed to validate the clinical utility of UE-CT and assess the reproducibility of these findings.

Ablation of Kidney Tumors in Patients with Substantial Kidney Impairment: Current Status

PURPOSE OF REVIEW

To review the current status of kidney tumor ablation in patients with substantial kidney impairment.

RECENT FINDINGS

Few reports of kidney tumor ablation in such patients have recently been published. The reported prevalence of patients with stage 4 or 5 chronic kidney disease (CKD) among patients undergoing ablation is 2.0%-10%. In patients with stage 4 or 5 CKD, local tumor control rates were 88%-100%. The effect of ablation on CKD stage is unclear, and the observed deteriorations in kidney function are consistent with both the effect of cryoablation and the natural course of advanced CKD. According to guidelines, active surveillance may be selected. The goals of treatment are complete tumor removal and maintenance of kidney function, both of which can be met by ablation. Given the limited treatment options, ablation may play a pivotal role in the management of patients with advanced CKD.