Radiology: Volume 253: Number 1-October 2009
Todd C.Schirmang, MD William W. Mayo-Smith, MD Damian E. Dupuy, MD Michael D. Beland, MD David J. Grand, MD
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-eompliant retrospective study. The study population consisted of 101 consecutive patients with 106 solid renal neoplasms that were treated with percutaneous UFA. 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.