Comparative Outcomes of Microwave Ablation Versus Surgery for Papillary Thyroid Microcarcinoma

Abstract

Background

Thyroid cancer, particularly papillary thyroid microcarcinoma (PTMC), is on the rise, with many patients opting for surgery despite evidence supporting active surveillance. This study compares the safety and efficacy of ultrasound-guided microwave ablation and traditional surgery for treating PTMC.

Material/Methods

A retrospective analysis was conducted on 30 patients with single-lesion PTMC treated with ultrasound-guided microwave ablation and 30 patients with single-lesion PTMC treated with conventional surgery. Clinical data and follow-up outcomes were compared between the 2 groups, assessing therapeutic efficacy and complications.

Results

Patients in the surgery group were more likely to experience postoperative hypothyroidism (P=0.004) and pain (P=0.007) than were those in the ablation group. In the ablation group, the maximum tumor diameter increased 1 month after the procedure, but significantly decreased at 6 to 12 months after treatment. After 6 months of follow-up, 19 patients (63.33%) in the ablation group had complete tumor disappearance. By the end of the follow-up period, all patients in the ablation group showed tumor shrinkage, with no local recurrence, cervical lymph node metastasis, or distant metastasis observed on re-examination.

Conclusions

Ultrasound-guided microwave ablation for the treatment of single-lesion PTMC without cervical lymph node metastasis is associated with outcomes comparable to those of traditional open surgery, with the added benefits of shorter hospital stays and a significantly reduced incidence of postoperative pain and other complications.

Introduction

According to the 2020 statistics from the International Agency for Research on Cancer of the World Health Organization, thyroid cancer ranks ninth in global cancer incidence, and its incidence has been steadily increasing in recent years [1,2]. Thyroid cancer encompasses several pathological types, with papillary thyroid carcinoma being the most common, accounting for 70% to 80% of all cases. With the rapid advancement of medical imaging techniques, the detection rate of small thyroid cancers has significantly increased. The World Health Organization defines papillary thyroid microcarcinoma (PTMC) as a papillary thyroid carcinoma with a maximum diameter not exceeding 10 mm [3]. Despite substantial evidence indicating that patients with low-risk PTMC, defined by thyroid nodules smaller than 10 mm and lacking other high-risk characteristics, exhibit comparable long-term mortality rates over nearly a decade of follow-up under active surveillance as those undergoing immediate surgery [4–6], many patients in clinical practice still choose traditional surgical treatment, due to the anxiety and perceived inconvenience associated with active surveillance. Ironically, recent study has shown that 24% of patients with low-risk PTMC who underwent thyroidectomy reported significant regret, due to a marked decline in thyroid-related quality of life [7]. Consequently, clinicians need to repeatedly balance the oncological benefits of surgery with the psychosocial burden of patients. Ultrasound-guided microwave ablation (MWA) is a commonly used method for treating benign thyroid nodules and has been increasingly applied for the treatment of papillary thyroid carcinoma [8,9]. However, there is limited research comparing the efficacy of MWA with that of traditional surgery in patients with PTMC. Therefore, this study aims to evaluate the effectiveness and safety of MWA in treating PTMC by comparing it with traditional surgery.

Material and Methods

General Information

This study was approved by the institutional review board of Zhongnan Hospital of Wuhan University, and written informed consent was obtained from all patients prior to the initiation of treatment. This study retrospectively analyzed the clinical data and follow-up information of all 30 patients with PTMC who underwent ultrasound-guided MWA from January 2021 to August 2023, categorized as the ablation group. Simultaneously, the same inclusion and exclusion criteria were used to screen 129 patients with PTMC who underwent traditional surgery during the same period. According to the random number table method, 30 patients were randomly selected at a ratio of 1: 1, and their clinical data and follow-up information were also collected. This was categorized as the surgery group. The follow-up ended in August 2024. The inclusion criteria were (1) Preoperative ultrasound suggesting a solitary suspicious nodule, not adherent to the capsule, with a maximum diameter ≤1 cm; (2) no obvious coarse calcifications within the suspicious nodule; (3) no evidence of cervical lymph node metastasis on imaging; (4) fine needle aspiration cytology confirming the diagnosis of papillary thyroid carcinoma; and (5) no family history of thyroid cancer. The exclusion criteria were (1) abnormal coagulation function or use of anticoagulant medications; (2) severe heart, lung, or other organ failure; (3) inability to cooperate with or tolerate thermal ablation treatment; (4) presence of a cardiac pacemaker or other metal implants; (5) other contraindications for MWA; (6) complete clinical data or follow-up data were not available; and (7) the follow-up time was less than 12 months.

Instruments

All MWA procedures were performed by doctors with more than 5 years of experience in thyroid ablation, each having completed at least 50 MWA cases prior to this study. Ablation treatment was performed using a Mindray M9 color Doppler ultrasound machine with a 12L high-frequency linear probe, coupled with an intelligent MWA system (Nanjing Great Wall) and single-use ablation needles (Nanjing Great Wall J-16-08), an instrument with a frequency of 2450 MHz and maximum transmitting power of 60 W. Patients were placed in the supine position with their shoulders raised to fully expose the neck region. The head was tilted toward the healthy side. Ultrasound was used to assess the lesion’s location and its relation to surrounding tissues. An appropriate needle insertion point was selected. Local anesthesia was applied using 1% lidocaine through a 5 mL syringe at the puncture site. Under ultrasound guidance, the needle tip was inserted into the gap between the thyroid capsule and surrounding tissues, and diluted lidocaine was injected to create an isolation zone, covering the thyroid’s upper and lateral aspects. Under real-time ultrasound guidance, the ablation needle was precisely advanced through the predetermined puncture site to the inferior pole of the target lesion. The ablation protocol was executed using a systematic craniocaudal approach, with therapeutic parameters meticulously tailored to individual lesion characteristics. For smaller tumors, fixed ablation was implemented. Larger tumor masses required application of a multipoint dynamic ablation technique, to ensure comprehensive coverage. The ablation protocol incorporated 30 W pulsed energy delivery in 25-s intervals, with real-time ultrasound monitoring of echogenic evolution within the treatment zone. The ablation field was strategically extended 5 mm beyond the tumor margins, to establish a safety buffer. Procedural termination criteria were met when intraoperative ultrasonography demonstrated complete encapsulation of the lesion by a homogeneous hyperechoic zone. Post-procedural verification was achieved through contrast-enhanced ultrasound, with definitive treatment confirmation requiring demonstration of non-enhancing characteristics within the ablation zone following contrast agent administration. The intervention concluded with localized cryotherapy application (ice pack compression) maintained for 30 min, to optimize hemostasis and tissue recovery, as shown in Figure 1. The traditional surgical approach involved thyroid lobectomy combined with isthmectomy and central lymph node dissection. The MWA procedure was minimally invasive, with local compression applied after the MWA through the puncture needle, showing no significant bleeding. In the surgical group, blood loss was estimated based on the amount of blood soaked in a 15×15 cm gauze pad, with each pad soaked in blood counted as 15 mL. Ablation procedures in our center followed a day surgery protocol, with a hospital stay of 1 day.

Figure 1.

Patient was a 46-year-old woman with diagnosis of papillary thyroid carcinoma on the left side via fine needle aspiration, who underwent ultrasound-guided microwave ablation (MWA) treatment. (A) Preoperative localization to assess the relationship between the tumor and surrounding vascular structures. (B) Ultrasound-guided injection of 10 mL of local anesthetic outside the thyroid capsule to create a safety margin. (C) Insertion of the ablation needle into the tumor for MWA treatment at 30 W power. (D) Six-month postoperative follow-up with thyroid ultrasound showing no abnormal echoes, after injection of 2.0 mL SonoVue into a superficial vein; ultrasound shows no significant abnormal enhancement in the original tumor area, with perfusion patterns similar to that of the surrounding thyroid tissue. The software WPS Office, 12.1.0.21171, Kingsoft Corp was used for creation of figures.

Observation Indicators

Patients were followed up for 1 year after surgery, with check-ups every 3 months. After the first year, check-ups were performed every 6 months. The follow-up assessments included cervical ultrasound, thyroid function tests, measurement of the maximum diameter of the ablation lesion, and recording the status of the lesion, post-operative hormone levels, complications, and progression at the time of the final follow-up.

Statistical Analysis

Statistical analyses were performed using SPSS 20.0 software. Continuous data with a normal distribution are expressed as mean±standard deviation (χ̄±s), and comparisons between groups were made using the independent samples t test. For data with a skewed distribution, the median and interquartile range [M(P25, P75)] are used, and group comparisons were performed using the Mann-Whitney U test. Categorical data are expressed as counts (%), with comparisons made using the χ² test or Fisher’s exact probability method. A P value of <0.05 was considered statistically significant.

Results

Clinical Characteristics

A total of 60 patients with PTMC were enrolled, all of whom were diagnosed with papillary thyroid carcinoma. The lesions were located in the left lobe in 27 cases (15 in the ablation group and 12 in the surgery group) and in the right lobe in 33 cases (17 in the ablation group and 16 in the surgery group). In the ablation group, there were 11 male and 19 female patients, with ages ranging from 31 to 46 years (mean age 38.2±3.83 years), and the maximum tumor diameter ranged from 5.7 to 8.9 mm (mean 7.18±0.84 mm). In the surgery group, there were 13 male and 17 female patients, with ages ranging from 33 to 46 years (mean age 39.7±3.71 years), and the maximum tumor diameter ranged from 5.4 to 9.3 mm (mean 7.46±0.99 mm). No significant differences were observed between the ablation and surgery groups in terms of age (P=0.128), sex (P=0.598), maximum tumor diameter (P=0.245), thyroid hormone levels (P=0.455, P=0.399, P=0.877), or follow-up duration (P=0.967) (Table 1).

Table 1.

Comparison of baseline data of microwave ablation group and surgery group.

	MWA	Surgery	t/Z/χ2	P
Age (y)	38.2±3.83	39.7±3.71	1.542	0.128
Maximal tumor diameter (mm)	7.18±0.84	7.46±0.99	1.173	0.245
Sex (Male)	11 (36.7%)	13 (43.3%)	0.278	0.598
FT3 (pmol/L)	5.16 (4.95, 5.22)	5.12 (4.97, 5.18)	0.747	0.455
FT4 (pmol/L)	13.93 (12.16, 14.39)	13.85 (12.51, 14.62)	0.849	0.399
TSH (μIU/mL)	2.13 (2.00, 2.64)	2.18 (2.06, 2.31)	0.155	0.877
Follow-up date (months)	27.63±5.46	27.57±6.75	0.042	0.967

FT3 – free T3; FT4 – free T4; TSH – thyroid stimulating hormone; MWA – microwave ablation.

Postoperative Outcomes in the MWA Group

In the MWA group, the average hospital stay was 1 day. All 30 patients completed the MWA treatment safely without any significant bleeding. The follow-up period ranged from 12 to 37 months, with a median follow-up of 28 months. During the follow-up, 6 patients reported significant postoperative swelling and pain, which improved notably after 3 days; 4 patients experienced transient neuropathy after treatment, all of which showed significant improvement after 1 week. Two patients had pain and transient neuropathy following the ablation treatment. The voice of all patients with transient neuropathy returned to normal during subsequent follow-ups, and no significant differences were observed, compared with their pre-treatment status. In total, 8 patients experienced postoperative complications. None of the patients experienced hematoma formation, transient or persistent hypothyroidism, or transient or persistent hypoparathyroidism during the follow-up period. Compared with pre-treatment measurements, the maximum tumor diameter at 1 month after treatment increased to 10.88±1.44 mm (t=25.89, P<0.001). At 6 months, 9 months, and 12 months after treatment, the tumor diameters were 3.11±0.33 mm (t=25.79, P=0.002), 2.64±0.27 mm (t=31.48, P=0.001), and 2.21±0.27 mm (t=37.07, P=0.001), respectively, showing significant changes (Table 2). At 1 month, 3 months, 6 months, and 9 months after treatment, the blood levels of FT3, FT4, and TSH showed no significant difference, compared with pre-treatment values (P>0.05 for all; Table 3). Compared with the traditional surgery group, the MWA group had significantly lower blood loss (Z=7.20, P<0.001), shorter hospital stay (Z=7.24, P<0.001), and fewer overall postoperative complications (χ²=6.79, P=0.009; Table 4). At the 6-month follow-up, 19 patients had complete resolution of the thyroid tumors after MWA treatment. At the 12-month follow-up, 5 patients opted for traditional surgery, due to persistent anxiety about residual disease, despite imaging confirmation of complete ablation (2 underwent surgery at 9 months and 3 at 12 months). Ultrasound imaging and postoperative pathology results of these patients did not reveal any significant abnormalities, as shown in Figure 2 and Table 5. By the end of the follow-up period, 25 patients who did not undergo surgery showed a reduction in the maximum tumor diameter. All patients were alive, with no signs of local recurrence, cervical lymph node metastasis, or distant metastasis during the follow-up.

Table 2.

Comparison of the longest diameter of lesions evaluated by ultrasound before and after microwave ablation treatment of papillary thyroid microcarcinoma.

Time	Maximal tumor diameter (mm)
Baseline (n=30)	7.18±0.84
1 Month after surgery (n=30)	10.88±1.44
3 Months after surgery (n=30)	5.83±0.75
6 Months after surgery (n=11)	3.11±0.33
9 Months after surgery (n=9)	2.64±0.27
12 Months after surgery (n=6)	2.21±0.27
18 Months after surgery (n=6)	1.89±0.23

Table 3.

Comparison of thyroid hormone levels before and after microwave ablation treatment of papillary thyroid microcarcinoma.

Time	FT3 (pmol/L)	FT4 (pmol/L)	TSH (μIU/ml)
Baseline	5.16 (4.95, 5.22)	13.93 (12.16, 14.39)	2.13 (2.00, 2.64)
After ablation
1 Month	5.12 (4.91, 5.19)	13.67 (12.06, 14.35)	2.04 (1.91, 2.51)
3 Month	5.14 (4.91, 5.20)	13.72 (12.10, 14.37)	2.08 (1.94, 2.58)
6 Month	5.15 (4.92, 5.21)	13.90 (12.13, 14.38)	2.12 (2.00, 2.62)
9 Month	5.17 (4.94, 5.21)	13.94 (12.16, 14.40)	2.14 (2.02, 2.66)
12 Month	5.17 (4.96, 5.22)	13.93 (12.17, 14.41)	2.14 (2.01, 2.64)

FT3 – free T3; FT4 – free T4; TSH – thyroid stimulating hormone.

Table 4.

Comparison of postoperative clinical data and complications between the microwave ablation (MWA) and surgery group.

	MWA	Surgery	Z/χ2	P
Hospital stay (days)	1.00	4 (4, 5)	7.24	<0.001
Blood loss (mL)	0	15 (10, 15)	7.20	<0.001
Overall complications	8	18	6.79	0.009
Pain	6	16	7.18	0.007
Hematoma	0	1	1.02	1.00
Hypoparathyroidism	0	2	2.07	0.47
Transient nerve paralysis	4	2	0.74	0.67

Figure 2.

Patient was a 39-year old woman with right-sided papillary thyroid microcarcinoma who underwent microwave ablation treatment and, after 9 months, voluntarily requested bilateral total thyroidectomy (A) Postoperative pathological specimen, front view. (B) Postoperative pathological specimen, side view. (C) Postoperative pathological specimen (histological view, acquired at 100× magnification, a scale bar representing 50 μm). (D) Preoperative ultrasound showing a hypoechoic area on the right side. The software WPS Office, 12.1.0.21171, Kingsoft Corp was used for creation of figures.

Table 5.

Data of 5 patients with papillary thyroid microcarcinoma undergoing conventional surgery after microwave ablation treatment.

Patient	Sex	Age	Location	MTD*	Latest ultrasonic examination	Contrast-enhanced ultrasound	Pathological findings	Central regional lymph nodes	Treatment**
1	Male	47	R	8	Hypoecho	Non-enhancement	No malignancy	0/7	R+I
2	Female	48	L	7	No abnormal echoes	Non-enhancement	No malignancy	0/6	L+I
3	Female	39	R	7	Hypoecho	Non-enhancement	No malignancy	0/7	B+I
4	Female	41	R	6	Hypoecho	Non-enhancement	No malignancy	0/8	R+I
5	Female	43	R	7	No abnormal echoes	Non-enhancement	No malignancy	0/9	R+I

MTD – maximal tumor diameter; R – right gland of thyroid; B – bilateral glands of the thyroid; I – isthmus thyroid.

Postoperative Outcomes in the Surgery Group

In the surgery group, the average hospital stay was 4.13±0.629 days, with an intraoperative blood loss of 14.67±3.46 mL. The median follow-up period was 26 months. During the follow-up, 9 patients developed transient hypothyroidism postoperatively, of which 8 also had postoperative pain, and 1 patient only developed hypothyroidism without pain. All patients with transient hypothyroidism returned to normal within 3 months after thyroid replacement therapy. Sixteen patients reported postoperative pain, all of which occurred on the first day after surgery and significantly improved within 2 to 3 days postoperatively. Two patients developed transient hypoparathyroidism after surgery, with 1 patient also experiencing postoperative pain and the other without additional complications; this transient hypoparathyroidism also returned to normal at subsequent follow-up. One patient developed a postoperative hematoma along with postoperative pain, and 2 patients experienced transient neuropathy, presenting as hoarseness. Both patients showed improvement by 1 month postoperatively. Two patients had both postoperative pain and transient neuropathy. In total, 18 patients experienced postoperative complications (Table 4). At the end of the follow-up period, all patients showed no signs of local tumor recurrence, cervical lymph node metastasis, or distant metastasis upon re-examination.

Discussion

With continuous advancements in medical technology, the detection rate of PTMC has significantly increased in recent years [3,10]. Although most studies suggest that PTMC has a slow tumor growth rate, low metastasis rate, and low mortality, active surveillance is recommended as a safe and reasonable alternative to traditional surgery for patients without high-risk features [6,11–13]. However, in clinical practice, many patients, due to anxiety and other psychological factors, ultimately opt for surgical treatment. Nonetheless, the risks of nerve injury, hypoparathyroidism, wound complications, and the need for postoperative thyroid hormone replacement therapy during traditional surgery remain difficult to avoid [14]. Medical professionals continue to seek a balance between the diagnosis of malignant tumors and good prognosis, as well as between the trauma of traditional surgery and the limitations of active surveillance. MWA, with its minimally invasive approach and lower risk of damage, has gradually become a new treatment option. The primary focus of this study is to compare the safety and effectiveness of MWA with that of traditional surgery for treating low-risk PTMC.

In this study, we retrospectively analyzed the preoperative and postoperative data of 30 PTMC patients treated with ultrasound-guided MWA and 30 PTMC patients who underwent traditional surgery during the same period. At the end of the follow-up, none of the patients in either group showed local recurrence or distant metastasis, indicating that the short-term prognosis of PTMC patients treated with MWA and traditional surgery was comparable. This finding aligns with a study by Zhang et al in 2020 [15]. Among the 30 patients treated with MWA, 19 patients (63.33%) had complete disappearance of the lesion, and all patients showed significant tumor shrinkage, compared with before the ablation. A meta-analysis by Tong et al in 2019 on thermal ablation of patients with PTMC showed a tumor disappearance rate of 57.3% to 76.2%, similar to our study’s results [16], further demonstrating the short-term effectiveness of ablation treatment, However, given the indolent biological behavior and favorable prognosis inherent to PTMC, despite methodological limitations in the present study, our findings align remarkably with comprehensive literature analysis. Notably, the extensive literature review revealed consistent clinical outcomes across multiple international studies. A landmark investigation by Li et al [17] demonstrated that patients undergoing radio frequency ablation for PTMC achieved an impressive 95.7% 8-year disease-free survival rate during a median follow-up period of 58.5 months. This conclusion is further corroborated by the longitudinal study of Cho et al [18], which reported complete absence of local recurrence, lymphatic metastasis, or distant dissemination in their cohort after an extended observation period averaging 67.8 months. In this study, thyroid hormone levels in patients treated with MWA were dynamically monitored, showing that the treatment caused minimal thyroid damage. Additionally, the hospital stay, intraoperative blood loss, and overall postoperative complications in the surgery group were significantly higher than those in the ablation group (P<0.05), suggesting that patients undergoing traditional surgery had a poorer postoperative outcome than did those undergoing MWA. Li et al (2019) reported a comparison of postoperative complications between traditional surgery and thermal ablation. In their study, the incidence of postoperative hypothyroidism, hypoparathyroidism, and recurrent laryngeal nerve injury in the surgery group was 100%, 7%, and 3%, respectively, while the thermal ablation group had rates of 0%, 0%, and 0.5% [19]. These results differ from those of our study, in which the postoperative complication rates were 30%, 6.67%, and 6.67% in the surgery group and 0%, 0%, and 13.33% in the ablation group. This difference could be due to the smaller sample size in our study. Although transient voice hoarseness and hormonal dysfunction typically resolve during the post-treatment recovery phase, the nuanced vocal quality alterations and psychological adaptation challenges associated with vocal metamorphosis regimens remain inadequately characterized. Current research paradigms have predominantly overlooked these critical aspects of patient experience, particularly the complex interplay between physiological adjustments and psychosocial adaptation during therapeutic transitions. Future investigations should prioritize comprehensive assessments incorporating objective vocal parameter analyses and validated psychometric evaluations through multidimensional longitudinal studies.

In our study, 5 patients treated with MWA later opted for traditional surgical resection for personal reasons. Preoperative thyroid ultrasound revealed that 2 patients still had hypoechoic areas, while 3 showed no abnormal echoes. However, ultrasound contrast imaging did not show significant enhancement, and postoperative pathology confirmed the absence of residual cancer cells. This suggests that the ultrasound evaluation after ablation might differ from ultrasound contrast imaging results, with contrast ultrasound possibly being more in line with the actual pathological findings, although this difference did not reach statistical significance (P=0.429). The postoperative pathology results of these 5 patients who underwent reoperation showed that MWA was effective in treating PTMC. Ding et al (2022) reported that 10 out of 12 patients (83.33%) treated with MWA had no residual cancer cells in postoperative pathology, which differs from our findings. This discrepancy may be due to the inclusion of multifocal cases in their study, which increased the risk of residual cancer after ablation [20].

During follow-up, we observed that about 1 month after MWA, the tumor size slightly increased. However, between 6 and 12 months, the tumor significantly reduced in size, and no notable changes were seen after 18 months. Similar results have been reported in some studies, but they did not address the reasons for the short-term enlargement of the tumor size [21]. We believe the early increase in tumor size after ablation could be related to tissue absorption and local edema after the procedure.

Our study is limited by its relatively small sample size, single-center data collection, and a comparatively short follow-up period. Regarding case selection, although the same inclusion and exclusion criteria were applied to both groups of patients, in clinical practice, clinicians or patients themselves may prefer traditional surgical treatment for larger tumors. Although no statistically significant difference was observed in this study, the limited sample size might potentially obscure certain biases inherent in this preference. While the short follow-up time may not be sufficient for many researchers to fully accept the results, the positive outcomes provide guidance for further exploration in PTMC diagnosis and treatment. With close follow-up, future studies could involve a larger patient cohort and longer follow-up periods, which would offer valuable data for future research.

Conclusions

In conclusion, ultrasound-guided MWA for treating single-lesion PTMC without cervical lymph node metastasis has similar short-term prognosis as traditional open surgery. For carefully selected low-risk PTMC patients undergoing active surveillance, MWA can represent a viable non-surgical alternative when managed through multidisciplinary evaluation, particularly in cases where patients are suboptimal surgical candidates or decline operative intervention. Further multi-center, long-term follow-up studies are needed to explore the potential of this treatment approach.