Histopathological evaluation of papillary thyroid carcinoma following thermal ablation.

PURPOSE: To characterize histopathological changes in surgically resected papillary thyroid carcinoma (PTC) following thermal ablation (TA), including residual tumor patterns with cellular viability assessment, peritissue adhesion, and temporal evolution of ablation zones.

METHODS

This retrospective study included 15 patients with 19 cytologically confirmed PTC lesions who underwent surgical resection following TA between January 2016 and July 2025 due to confirmed or suspected lymph node metastasis, new PTC, failed TA, or patient anxiety. Specimens were processed for hematoxylin and eosin staining. For residual tumor areas exhibiting sublethal thermal injury, CD34 and Ki67 immunohistochemistry were performed to evaluate microvessel density and proliferative activity.

RESULTS

Complete ablation was achieved in 12/19 tumors (63.2%); 7 (36.8%) had residual disease with two patterns: central residuals (n = 5) exhibiting sublethal thermal injury with heterogeneous CD34/Ki67 expression (2 cases showed functional inactivation while 3 retained proliferative potential), and peripheral residuals (n = 2) from insufficient ablation margins. Among 13 capsule-adjacent tumors (≤2 mm), 6 (46.2%) developed adhesions, including 4 with thermal muscle injury and 2 with mild fibrous adhesion. Ablation zones evolved temporally: three-layer structure with inflammation (0-3 months), chronic inflammation with progressive fibrosis (4-12 months), and mature scar (>12 months).

CONCLUSION

This study characterized histopathological changes following TA for PTC, revealing two residual tumor patterns with distinct biological viability, a predictable evolution of ablation zones, and a close association between peritissue adhesion and thermal field management. Rigorous operator training and standardized protocols are essential for optimizing treatment efficacy and advancing the application of TA in PTC management.