The Efficacy and Safety of Radiofrequency Ablation for Trachea-Adjacent cT1N0M0 Papillary Thyroid Carcinoma: a five-year follow-up study

Technical Summary: Efficacy and Safety of RFA for Trachea-Adjacent cT1N0M0 PTC

Problem Statement
Papillary thyroid carcinoma (PTC) is the most common thyroid malignancy, typically characterized by an indolent course and favorable prognosis. While surgery remains the gold standard, Radiofrequency Ablation (RFA) has emerged as a viable alternative for low-risk, non-metastatic cases, particularly for patients who are poor surgical candidates or refuse surgery due to fears of complications like hypothyroidism. However, current clinical guidelines recommend a safety margin of ≥2 mm between the lesion and the trachea when performing RFA. A significant subset of patients presents with cT1N0M0 PTC lesions located adjacent to the trachea (<2 mm). The proximity of these lesions to critical structures, such as the recurrent laryngeal nerve (RLN) and the trachea itself, raises concerns regarding the safety of RFA, specifically the risk of thermal injury and incomplete ablation. There is a lack of robust evidence validating whether RFA can be safely and effectively applied to trachea-adjacent lesions without increasing the risk of complications or disease progression compared to distant lesions.

Methodology
This study is a retrospective cohort analysis conducted at Xuanwu Hospital, Capital Medical University, involving 423 patients with 563 cT1N0M0 PTC nodules treated between October 2020 and December 2023.

• Inclusion Criteria: Patients with FNA-confirmed PTC ≤2 cm, no extrathyroidal extension (ETE), no cervical lymph node metastasis (LNM), no distant metastasis, and no high-risk subtypes. Patients were either ineligible for or refused standard surgery (SR) or active surveillance (AS).
• Grouping: Lesions were categorized based on the distance to the trachea:
  • Trachea-adjacent group: Distance ≤2 mm (102 lesions, 18.1%).
  • Trachea-distant group: Distance >2 mm (461 lesions, 81.9%).
  • The adjacent group was further subclassified by contact extent: no contact, partial contact (<50%), and extensive contact (≥50%).
• Procedure: All RFA procedures were performed by a single experienced radiologist using ultrasound guidance. Key technical measures included:
  • Hydrodissection: Injection of 0.9% saline to create a fluid barrier between the tumor and adjacent structures (trachea, esophagus, nerves).
  • Ablation: Performed from deep to superficial using an 18G internally cooled electrode (10–60 W power).
  • Verification: Contrast-enhanced ultrasound (CEUS) was used immediately post-ablation and during follow-ups to confirm complete ablation (absence of enhancement).
• Follow-up: Patients were monitored at 1, 2, 3, 6, 9, 12, 15, 18, 24, 36, 48, and 60 months. Outcomes measured included complete absorption rate, disease-free survival (DFS), disease progression (residual lesions, new lesions, LNM), and complications.
• Statistical Analysis: Comparisons between groups utilized t-tests, Mann-Whitney U tests, and chi-square tests. Logistic regression (univariate and multivariate) was employed to identify independent risk factors for complications.

Key Contributions

1. Validation of Safety and Efficacy: The study provides empirical evidence that RFA is effective for cT1N0M0 PTC lesions located ≤2 mm from the trachea, demonstrating outcomes comparable to lesions located further away.
2. Risk Factor Identification: The research identifies specific anatomical and procedural factors associated with complications. Multivariate analysis confirmed that dorsal thyroid location and extensive tracheal contact (≥50%) are independent risk factors for complications.
3. Technique Optimization: The study highlights the critical role of the lateral lobe puncture approach and refined hydrodissection techniques in mitigating risks, particularly for high-risk anatomical locations (dorsal aspect, lower pole of the left lobe).
4. Long-term Follow-up Data: The study offers a five-year follow-up dataset, addressing a gap in literature regarding the long-term stability of RFA outcomes for trachea-adjacent nodules.

Results

• Efficacy: There was no statistically significant difference in complete absorption rates or disease-free survival between the trachea-adjacent and trachea-distant groups at any follow-up interval (24, 36, 48, and 60 months; all p > 0.05).
  • At 60 months, complete absorption rates were 100.0% for the trachea-adjacent group and 100.0% for the trachea-distant group.
• Disease Progression: Overall progression occurred in 10 patients (2.36%).
  • Trachea-adjacent group: 3 cases of new lesions (no residual lesions, no LNM).
  • Trachea-distant group: 5 cases of new lesions and 2 cases of LNM.
  • All progression cases were successfully managed with re-RFA, achieving complete absorption. No LNM occurred in the trachea-adjacent group.
• Complications:
  • Total complication rate: 3.5% (15/423).
  • Trachea-adjacent group: 11.5% (11/96).
  • Trachea-distant group: 1.2% (4/327).
  • The difference was statistically significant (p < 0.05). However, all complications occurred within 3 months and resolved without permanent sequelae (e.g., no permanent RLN injury).
• Risk Factors:
  • Independent risk factors for complications included dorsal nodule location and extensive tracheal contact.
  • Lesions in the left lower pole were more frequently associated with complications.
  • Complication rates were higher in procedures performed before 2023, suggesting a learning curve effect where improved technique (specifically lateral lobe puncture) reduced risks.

Significance and Claims
The authors conclude that with precise preoperative evaluation, optimized operative techniques (including hydrodissection and lateral lobe puncture), and rigorous assessment, RFA is a relatively effective and safe treatment option for cT1N0M0 PTC located adjacent to the trachea. The study suggests that RFA can expand therapeutic options for patients who are intolerant to or refuse surgery, even when lesions are in close proximity to the trachea (<2 mm). The authors emphasize that while complication rates are higher in the adjacent group, the absence of permanent complications and the high rate of complete absorption support the viability of this approach in experienced hands. The study acknowledges limitations, including its retrospective nature and single-center design, and calls for prospective trials to further validate these findings.