This study aimed to evaluate the feasibility and efficacy of ultrasound-guided percutaneous microwave ablation (MWA) in the treatment of low-risk papillary thyroid microcarcinoma (PTMC), and to observe the histopathological changes after MWA.

MWA was performed under ultrasound guidance for 73 unifocal PTMC patients without clinically cervical or distant metastasis. The target ablation zone exceeded the tumor edge (judged by contrast-enhanced US) to avoid marginal residue and recurrence. Ultrasound evaluation was performed at 1 day, 1, 3, 6, 12 and 24 months after treatment, and thyroid function evaluation at the first 6 months. Repeated fine needle aspiration cytology or core needle biopsy pathology was performed at 3 or 6 months after MWA to evaluate residual tumors. Any adverse event associated with MWA was evaluated.

The follow-up after MWA lasted 6 (6, 12) months. Tumor volume decreased significantly from 0.06 mm³ (0.04, 0.11 mm³) to 0.03 mm³ (0.00, 0.06 mm³) at 12 months after MWA (P< 0.001), with a median volume reduction ratio of 80.28% (-7.43, 100%) and 16 cases (21.92%) presenting complete remission. The largest diameter, volume and ablation energy were found to be different in patients with and without complete remission 12 months after MWA. On histopathological examinations, no atypical or malignant follicular cells were identified after thermal ablation. The most common pathological characteristics were fibroblastic proliferation (34/39, 87.18%) and chronic inflammation (32/39, 82.05%), followed by infarction (21/39, 53.85%). Five patients were transferred to thyroidectomy and 4 of them were confirmed with local recurrence and/or lymph node metastasis. Serum thyrotropin decreased transiently after MWA (P< 0.01) but normalized thereafter. No serious and permanent complications were reported.

MWA is a safe and effective treatment for low-risk PTMC. Fibroblastic proliferation and chronic inflammation are the most common pathological changes after MWA of PTMC.

本研究旨在评价超声引导下经皮微波消融（MWA）治疗低危甲状腺微小乳头状癌（PTMC）的可行性和疗效，并观察MWA术后的组织病理学变化。

在超声引导下对 73 例无临床宫颈或远处转移的单灶性 PTMC 患者进行 MWA。目标消融区超出肿瘤边缘（由增强超声判断）以避免边缘残留和复发。治疗后1天、1、3、6、12、24个月进行超声评估，前6个月进行甲状腺功能评估。在 MWA 后 3 或 6 个月进行重复细针抽吸细胞学或核心针活检病理学以评估残留肿瘤。评估了与 MWA 相关的任何不良事件。

MWA后随访6（6、12）个月。在 MWA 后 12 个月，肿瘤体积从 0.06 mm ³ (0.04, 0.11 mm ³ )显着减少到 0.03 mm ³ (0.00, 0.06 mm ^{3 ) (}磷< 0.001)，中位减容率为 80.28% (-7.43, 100%)，16 例 (21.92%) 完全缓解。发现 MWA 后 12 个月完全缓解和未完全缓解的患者的最大直径、体积和消融能量不同。在组织病理学检查中，热消融后未发现非典型或恶性滤泡细胞。最常见的病理特征为成纤维细胞增殖（34/39, 87.18%）和慢性炎症（32/39, 82.05%），其次为梗死（21/39, 53.85%）。5例患者转入甲状腺切除术，其中4例确诊局部复发和/或淋巴结转移。MWA 后血清促甲状腺激素短暂下降（磷< 0.01) 但此后标准化。没有报告严重和永久性并发症。

MWA 是一种安全有效的低风险 PTMC 治疗方法。成纤维细胞增殖和慢性炎症是PTMC MWA后最常见的病理变化。