Kidney neoplasms: renal halo sign after percutaneous radiofrequency ablation--incidence and clinical importance in 101 consecutive patients.

PURPOSE: To describe the incidence and clinical importance of the renal halo sign after percutaneous radiofrequency ablation (RFA) of renal neoplasms. MATERIALS AND METHODS: Institutional review board approval was obtained for this HIPAA-compliant retrospective study. The study population consisted of 101 consecutive patients with 106 solid renal neoplasms that were treated with percutaneous RFA. Postablation computed tomographic (CT) and magnetic resonance (MR) images were retrospectively reviewed by three board-certified radiologists to determine the presence of the renal halo sign. Statistical analyses were performed to determine reader agreement and assess the effect that tumor size and location, radiofrequency (RF) applicator type, RFA treatment time and success, maximum RFA treatment temperature, and number of RF applications performed had on development of the renal halo sign. RESULTS: The renal halo sign developed in 79 (75%) of the 106 ablated tumors. Average imaging follow-up lasted 25 months (range, 1-98 months). The renal halo sign appeared, on average, 6 months (range, 1 month to 3 years) after RFA. The renal halo sign resolved in five (6%) of 79 tumors treated. Interobserver agreement for the presence of the renal halo sign was high. Tumor size and location, RF applicator type, RFA treatment time and success, maximum RFA treatment temperature, and number of RF applications performed were not independent predictors of renal halo sign development. CONCLUSION: The renal halo sign is seen in 75% of patients after percutaneous RFA of renal neoplasms. It may decrease in size over time; however, it rarely disappears. It is important to recognize this sign, as it can be mistaken for recurrent tumor or angiomyolipoma by radiologists who are not familiar with RFA.

Image-guided thermal ablation of nonresectable hepatic tumors using the Cool-Tip radiofrequency ablation system.

Percutaneous thermal ablation techniques have gained considerable attention as an alternative to surgery for the treatment of malignant liver tumors in selected patients. In particular, image-guided radiofrequency ablation (RFA) is increasingly being used for the local treatment of hepatocellular carcinoma, as well as for metastases to the liver. As a minimally invasive treatment option, this technique has several advantages compared with surgical resection. Benefits include reduction in morbidity and mortality, lower cost, suitability for real-time imaging guidance, use in an outpatient setting and use in patients who are not surgical candidates. The Cool-Tip RFA system has recently received US FDA approval for use in ablating nonresectable liver tumors. This article describes the principles and application of radiofrequency ablation for the treatment of nonresectable hepatic tumors along with the unique features of the Cool-Tip RFA system. Finally, a view into the future suggests that, as the trend towards minimally invasive treatment options for hepatic malignancies continues, RFA will assume increasing clinical application.