Kidney Neoplasms: Renal Halo Sign after Percutaneous Radiofrequency Ablation—Incidence and Clinical Importance in 101 Consecutive Patients

Abstract

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.

Solid renal masses: effectiveness and safety of image-guided percutaneous radiofrequency ablation

“…4). This appearance can be seen on both CT and MRI, and has been described in up to 75% of treated lesions [60], most commonly occurring when the initial treated lesion was peripheral or exophytic in location [58,59]. On MRI, the surrounding thin soft tissue halo usually demonstrates variable T1 and T2 signal intensity, but the central lesion should remain T2 dark and non-enhancing.…”

“…There is currently no established surveillance imaging protocol for these patients, however, some institutions obtain imaging follow-up at 1, 3, and 6 months after treatment, then annually thereafter. On follow-up imaging, treated lesions commonly demonstrate a ''halo sign'' manifest as a central nonenhancing soft tissue mass (treated lesion) surrounded by fat and a thin rim of peri-tumoral soft-tissue attenuation (halo) [60]. There is often associated atrophy of the adjacent renal parenchyma (Fig.…”

Treatment of focal benign lesions of the bone: MRgFUS and RFA

“…This sign is found also when treating the bone 26 and other structures. [27][28][29] On MRI T 2 weighted sequences, the halo or ring sign generally appears as a round central area characterized by low signal intensity surrounded by a peripheral isohyperintense rim; the CT pattern is very similar and appears as a central hypodense zone surrounded by a rim with higher density. …”

Laparoscopic and Image-guided Radiofrequency Ablation of Renal Tumors: Patient Selection and Outcomes

“…Most ablations are performed in patients with small renal masses (SRM; <4 cm). Mean tumor sizes in RFA series range from 1.7 to 3.8 cm [26,[28][29][30][31][32][33][34][35][36]. About 80% of resected SRMs are malignant [37]; however, biopsy results in RFA series have shown RCC in 48% to 91% of studies [6, 10••, 26, 29], with some series reporting exclusively malignant tumors [36,38].…”