Efficacy And Safety Of Microwave Ablation In The Treatment Of Low-risk Papillary Thyroid Microcarcinoma

Objective:To investigate the efficacy and safety of ultrasound-guided percutaneous microwave ablation(MWA)for the low-risk papillary thyroid microcarcinoma(PTMC).Methods:From December 2017 to December 2020,a total of 55 patients with 55 low-risk PTMC were treated with MWA.Postoperative follow up at 1 day,1 month,3 months,6 months,1 year and 2 years were conducted.Thyroid function test,nodule volume,complications and tumor persistence/recurrence were evaluated.Repeated fine needle aspiration cytology or core needle biopsy pathology and molecular test were performed at 3 or 6 months after MWA.Histopathologic characteristics was observed.We analyzed the data about volume reduction,disappearance of ablated areas,thyroid function,histopathology after MWA,complications,recurrence or metastasis.Results:Totally,55 patients were enrolled.The median age was 39(P25,P75:28.00,47.00)years old.The male to female ratio was 12:43.The medium largest diameter and volume of preoperative PTMC were 0.53(0.43,0.69)cm and 0.05(0.03,0.12)cm3,respectively.The medium follow-up period was 6(3,12)months.CNB and 1 FNAC were performed for 28 patients and 1 patient after MWA at 3-6 months follow up,with no residual tumor cells found,respectively.We found BRAF V600E mutation in 3 patients who received molecular test 3 months after MWA.Among them,1 patient was referred to surgery.The volume of ablated areas increased rapidly,then decreased to the preoperative size at 6 months.The volume of preoperative PTMC and ablated area 6 months after MWA was 0.05(0.03,0.12)and 0.08(0.02,0.17)(P=0.117),respectively.The volume reduction rate at 1 day and 1,3,6,12 months was-2886.98(-5257.14,-933.31)%,1250.731(-2260.87,-614.80)%,-358.78(-872.33,-132.04)%,-36.99(-268.25,83.73)%,70.20(-6.08,100)%,respectively.Disappearance of ablated areas was found within 1 year after ablation and totally 12.73%ablation zones were absorbed completely during postoperative follow up.Completely absorption at 6 months were found in 6 patients,of whom the tumor volume(P=0.013),maximal diameter(P=0.041)and age(P=0.033)were significantly different from those who had existed nodules.Significant differences of ablated zone(P=0.003)and delivery energy(P=0.010)were found between patients with enlarged and shrunk ablated areas.The most common pathological characteristic after MWA was fibroblastic proliferation(21/25,84.00%)followed by chronic inflammation(20/25,80.00%).And the least common change was acellular hyalinization(1/25,4.00%).None of the patients received a thyrotropin(TSH)suppression therapy.A transient decrease in TSH(P<0.01)with an increase in free thyroxine(P<0.01),free triiodothyronine(P<0.01),thyroglobulin(P<0.01)and thyroglobulin antibody(P<0.01)was observed after MWA but thyroid function normalized within 1 month after MWA.Most MWA associated thyroid dysfunction including hyperthyroidism and hypothyroidism recovered spontaneously.MWA seemed not to aggravate pre-existing hypothyroidism.Mild neck pain,the most common complication,usually recovered within one week.A transient hoarseness was reported and recovered 3 months later.One patient was found to have a permanent hypothyroidism with the need of levothyroxine treatment.None of the patients reported serious or permanent complications expect one hypothyroidism.Conclusion:MWA is safe and effective in the treatment of low-risk PTMC.Ablated area after MWA disappears much faster in the younger patients with a smaller PTMC.The volume reduction rate is associated with the volume of ablated zone and delivered microwave energy.