Novel approach of thyroid radiofrequency ablation for huge nodules-Eggshell technique (evenly margin-preserving ablation): a case report

Abstract

Background: Radiofrequency ablation (RFA) for huge thyroid nodules often requires multiple sessions to achieve long-term efficacy. We present our experience with a stepwise approach utilizing a nodule margin-preserving ablation, termed the Eggshell technique, in the treatment of a thyroid nodule exceeding 9 cm in diameter.

Case description: A 44-year-old woman presented with compressive symptoms due to a large left thyroid solid nodule measuring 5.81 cm × 3.19 cm × 9.26 cm, with a volume of 90.84 mL. Cytopathology, including core needle biopsy, confirmed Bethesda Category II in two separate evaluations. RFA was performed under local anesthesia using the Eggshell technique, which preserved the nodule margin while ablating the internal tissue. The procedure lasted 83 minutes, delivering a total energy of 38.59 kJ. At 6 months, the nodule volume decreased to 29.75 mL [volume reduction ratio (VRR) 67.25%]. After three additional sessions, the volume further reduced to 1.59 mL (VRR 98.25%) at 42 months. The patient experienced minimal pain (pain score 1), with no hemorrhage, post-ablation edema, or nodule rupture. Serial ultrasonography allowed precise visualization of residual tissue, optimizing the timing of subsequent ablations.

Conclusions: This case suggests that the Eggshell technique, an evenly margin-preserving RFA strategy, may be a valuable option for managing huge thyroid nodules that inevitably require multiple sessions. By minimizing patient discomfort and complications, and facilitating decision-making during follow-up, this approach can complement conventional RFA techniques for large nodules.

Keywords: Thyroid; case report; goiter; radiofrequency ablation (RFA); technique.

Figure 1

Eggshell technique of RFA. (A) The Eggshell technique of RFA is utilized when treating huge nodules where it is inevitable to have a viable portion remaining post-treatment. This technique involves treating the interior of the nodule while maintaining a consistent distance from surrounding structures. (B) After the central portion of the nodule has been adequately absorbed as observed in follow-up ultrasound examinations, reassessment is conducted. If necessary, the same technique is repeated. Once the nodule is sufficiently separated from surrounding structures, complete ablation of the nodule is performed. (C) An oblique view of a treated thyroid nodule shows uniform reduction towards the center, indicating a centripetal pattern. This allows for easier prediction of the treated and retained portions of the nodule during follow-up observations after RFA, minimizing damage to surrounding tissues and providing flexibility in selecting additional treatment options. RFA, radiofrequency ablation.

Figure 2

Patient profile and thyroid US. (A) A 44-year-old female presenting with an anterior neck bulge and pressure symptoms. (B) US shows a predominantly solid, isoechoic nodule in left thyroid lobe, measuring 5.81 cm × 3.19 cm × 9.26 cm (width × depth × height), with an estimated volume of 90.84 mL. The nodule was confirmed to be benign based on two cytopathologic evaluations, including one core needle biopsy. US, ultrasonography.

Figure 3

Timeline of case progression. Chronological summary of key clinical and imaging findings. (A₁,A₂) US immediately after the first RFA using the Eggshell technique shows intentionally preserved viable tissue at the nodule margin. No edema or hematoma is observed within the nodule or surrounding thyroid parenchyma. (B) Six-month follow-up US demonstrates a reduction in nodule volume, with shrinkage of the central ablated area. The volume decreased to 29.75 mL, suitable for the pre-planned remote access thyroidectomy. However, the patient opted to continue with RFA, and a second session using the Eggshell technique was performed. (C) Eight months after the second RFA, US reveals exposure of the anterior and lateral thyroid parenchyma surrounding the nodule. The nodule volume had decreased to 15.51 mL, making any treatment modality feasible. The patient chose to proceed with a third RFA, and surgical intervention was no longer considered. Complete ablation was achieved using the conventional RFA technique. (D₁,D₂) Ten months after the third RFA, US shows a further reduction in volume to 5.29 mL. Color Doppler reveals intranodular vascularity, and an additional RFA session was performed to prevent regrowth. (E₁-E₃) Eighteen months after the fourth RFA (42 months after the initial RFA), the nodule volume decreased to 1.59 mL. Symptom resolution was achieved, and perilesional vascularity markedly decreased. RFA, radiofrequency ablation; US, ultrasonography.

Figure 4

Conventional thyroid RFA procedure. During initial treatment, most of the nodule is ablated, except for areas adjacent to the tracheoesophageal groove (“danger triangle”) and major surrounding structures. Asterisk indicates undertreated viable portions of the nodule. (A) Pre-treatment ultrasonography shows an isoechoic thyroid nodule approximately 20 mL in volume (confirmed to be benign based on two separate cytopathologic evaluations), causing nodule-related symptoms. (B) Immediate post-RFA image following selective preservation of areas adjacent to the danger triangle and carotid sheath. (C) Seven months post-RFA. As the treated area shrinks over time, multiple residual lesions appear unintentionally along the nodule margins. (D) Thirty-four months post-RFA. Most of the ablated area has been absorbed, with residual lesions observed along the nodule periphery. At this stage, hydrodissection was employed to protect adjacent structures during additional RFA. (E) Nineteen months after the additional RFA. The nodule is now seen as a small, scar-like remnant. RFA, radiofrequency ablation.