Abstract
Background:
Ultrasound-guided thermal ablation has become an established alternative to surgery for benign thyroid nodules. Hydrodissection is routinely used to protect adjacent critical structures; however, assessment of its adequacy remains subjective, with no standardized imaging marker to confirm procedural readiness before energy delivery. This prompted us to describe and evaluate a novel ultrasound imaging marker, the ring of protection (RoP) sign, designed to confirm complete circumferential hydrodissection and enhance procedural safety during microwave ablation (MWA) of benign thyroid nodules.
Methods:
The ring of protection sign is defined as a continuous circumferential anechoic fluid rim completely surrounding the target thyroid nodule, visible in 2 orthogonal ultrasound planes, persisting during gentle probe compression, and eliminating direct contact between the nodule and adjacent critical structures. We detail the technical methodology, sonographic criteria, and clinical application of the ring of protection sign during ultrasound-guided MWA. Outcomes of patients treated using ring of protection-guided hydrodissection (RoP group) were compared with those undergoing standard hydrodissection (HD group).
Results:
Sixty-three patients were included (HD: n=28; RoP: n=35), with comparable baseline demographic and nodule characteristics. Mean procedure time was significantly shorter in the RoP group (20±10 vs. 26±13 min;
P
=0.049). No major complications occurred in either group. Minor complications, volume reduction ratios (at 6 and 12 mo), postprocedural pain, and cosmetic outcomes were similar between groups.
Conclusion:
The ring of protection sign is a simple, reproducible, and clinically meaningful ultrasound marker that provides objective confirmation of adequate hydrodissection before thyroid thermal ablation. Its adoption may help standardize procedural readiness assessment, improve training consistency, and further enhance the safety profile of thyroid ablation techniques.