Radiofrequency Ablation, Where It Stands in Interventional Radiology Today

Hepatic Hilar Nerve Block for Adjunctive Analgesia during Percutaneous Thermal Ablation of Hepatic Tumors: A Retrospective Analysis

PURPOSE

To determine whether hepatic hilar nerve block techniques reduce analgesic and sedation requirements during percutaneous image-guided thermal ablation of hepatic tumors.

MATERIALS AND METHODS

A single-center retrospective cohort analysis was performed of 177 patients (median age, 67 years; range, 33-86 years) who underwent percutaneous image-guided thermal ablation of liver tumors. All patients were treated utilizing local anesthetic and moderate sedation between November 2018 and November 2021 at a tertiary level hospital, with or without the administration of a hepatic hilar nerve block. Univariable and multivariable linear regression analyses were performed to determine the relationship between the administration of the hilar nerve block and fentanyl and midazolam dosages.

RESULTS

A total of 114 (64%) patients received a hilar nerve block in addition to procedural sedation, and 63 (36%) patients received procedural sedation alone. There were no significant differences in the baseline demographic and tumor characteristics between the cohorts. The procedure duration was longer in the hilar block cohort than in the unblocked cohort (median, 95 vs 82 minutes; P = .0012). The technical success rate (98% in both the cohorts, P = .93) and adverse event rate (11% vs 3%, P = .14) were not significantly different between the cohorts. After adjusting for patient and tumor characteristics, ablation modality, and procedure and ablation durations, hilar nerve blocks were associated with lower fentanyl (-18.4%, P = .0045) and midazolam (-22.7%, P = .0007) dosages.

CONCLUSIONS

Hepatic hilar nerve blocks significantly decrease the fentanyl and midazolam requirements during thermal ablation of hepatic tumors, without a significant change in the technical success or adverse event rates.

Percutaneous microwave ablation versus radiofrequency ablation of hepatocellular carcinoma: a meta-analysis of randomized controlled trials

PURPOSE

Percutaneous radiofrequency ablation (RFA) and microwave ablation (MWA) are well-validated interventions for hepatocellular carcinoma (HCC). The purpose of this study was to compare their safety and efficacy through a meta-analysis of randomized controlled trials (RCT).

METHODS

MEDLINE, Pubmed, and the Cochrane Library were queried up to September 2020 using the terms "microwave", "radiofrequency", "hepatocellular", and "randomized". Only RCTs investigating MWA versus RFA for HCC were included. Baseline study characteristics, complete ablation rate, ablation time, overall survival, local recurrence, and complication rates were investigated.

RESULTS

Among the five original studies included, a total of 413 and 431 patients were treated with RFA and MWA, respectively. All studies focused on very early and early-stage HCC only (Barcelona Clinic Liver Cancer Stage 0 and A). No statistical significance was observed in terms of complete ablation rate (96.7 vs 96.9%, p = 0.882), overall survival (6 month: 95.7 vs 100%, p = 0.492; 1 year: 91.9 vs 94.1%, p = 0.264; 3 year: 77.5 vs 78.4%, p = 0.905), recurrence-free survival (6 month: 99.1 vs 99.7%, p = 0.717; 1 year: 94.6 vs 93.9%, p = 0.675; 3 year: 76.8 vs 77.1%, p = 0.935), and complication rates (p > 0.05 in all types). The mean ablation time of MWA was significantly shorter than RFA (26.9 vs 14.1 min, p < 0.001).

CONCLUSION

For very early and early-stage HCC, RFA and MWA are equally safe and effective, though the former is associated with a longer ablation time.

Parametric evaluation of impedance curve in radiofrequency ablation: A quantitative description of the asymmetry and dynamic variation of impedance in bovine ex vivo model

Radiofrequency ablation (RFA) is a treatment for liver tumors with advantages over the traditional treatment of surgical resection. This procedure has the shortest recovery time in early stage tumors. The objective of this study is to parameterize the impedance curve of the RFA procedure in an ex vivo model by defining seven parameters (t_1/2, t_minimum, t_end, Z_initial, Z_1/2, Z_minimum and Z_end). Based on these parameters, three performance indices are defined: one to identify the magnitude of impedance curve asymmetry (δ), one Drop ratio (DR) describing the percentage of impedance decrease until the minimum impedance point is reached, and Ascent Ratio (AR) describing the magnitude of increase in impedance from the minimum impedance point to its maximum point. Fifty ablations were performed in a bovine ex vivo model to measure and evaluate the proposed parameters and performance index. The results show that the groups had an average δ of 29.02%, DR of 22.41%, and AR of 545.33% for RFA without the use of saline or deionized solutions. The saline solution and deionized water-cooled groups indicated the correlation of performance indices δ, DR, and AR with the obtained final ablation volume. Therefore, by controlling these parameters and indices, lower recurrence is achieved.

Radiofrequency Ablation by a 21-Gauge Internally Cooled Electrode: Ex Vivo and In Vivo Evaluation by Rat Liver

PURPOSE

To evaluate the coagulative performance of a 21-gauge (G) internally cooled radiofrequency (RF) electrode using ex vivo and in vivo rat liver.

MATERIALS AND METHODS

We developed a prototype of 21-G internally cooled monopolar RF electrode with 5.0 mm active tip length. The ablative zone size created by this electrode was evaluated in ex vivo and in vivo rat liver. Five RF powers (3 W, 5 W, 7 W, 9 W, and 11 W) were applied with and without circulation of chilled water within the electrode. The ablation zone sizes were compared. Histopathological evaluation of the ablation zone was also performed at 24 h and at 7 days after RF ablation.

RESULTS

From ex vivo experiments, the ablation volume was found to increase significantly when RF energy was applied with the chilled water circulation. Results of in vivo experiments demonstrate that the ablation volume reached its maximum value when RF power of 7 W was applied (532.3 ± 110.3 mm³). Histopathological examination showed delineated coagulation necrosis at 24 h after RF ablation, which clarified the ablation zone border. Fibrotic change was also observed at 7 days after RF ablation.

CONCLUSION

RF ablation using a 21-gauge electrode produced coagulation necrosis in the rat liver. The ablation volume became maximum when RF power of 7 W was applied with chilled water circulation.