Predictors of metastasis in cervical indeterminate lymph nodes after thyroid cancer ablation by long-term ultrasound follow-up

Abstract

Objectives

To investigate the pattern of change over time and predictors for metastasis in indeterminate lymph nodes (LNs) among patients with thyroid cancer post-ablation.

Methods

We enrolled patients who developed new cervical LNs after papillary thyroid carcinoma (PTC) ablation. Changes in the ultrasound characteristics of the indeterminate LN were recorded at months 1, 3, 6 and 12 after ablation. LN puncture pathology and long-term follow-up were standard of diagnosis. The indeterminate LNs were divided into benign and malignant groups, the differences between the two groups were compared, and the risk characteristics of malignant LNs were screened using generalized estimating equations (GEE).

Results

In total, we included 138 LNs from 99 patients, of which 48 were indeterminate LNs. When following up indeterminate LNs, non-cervical lymph node metastasis (non-CLNM) lesions demonstrated a statistically significant gradual decrease in volume (p = 0.012), though there was no significant change in the volume of CLNM lesions (p = 0.779). Compared to non-CLNM lesions, the diagnostic efficiency was the highest for CLNM lesions at 1–3 months after ablation, when the LN volume changed by −0.08 to 0.12 mL (p = 0.048). The third month after ablation became an important time point for review. Moreover, GEE analysis showed that microcalcifications, cystic changes, and vascularity were strongly associated with CLNMs (p = 0.004, p = 0.002, and p = 0.010, respectively).

Conclusions

There is a pattern of volume change of indeterminate LNs after PTC ablation, which, together with microcalcifications, cystic changes, and vascularity, can be used as criteria for differentiating the benignity and malignancy of indeterminate LNs.

Keywords:

• Ultrasonography
• thyroid neoplasms
• lymph nodes
• lymphatic metastasis

Introduction

Papillary thyroid carcinoma (PTC) is the most common histological type of thyroid carcinoma, accounting for 80%–90% of differentiated thyroid carcinomas [1]. The 2015 American Thyroid Association Management (ATA) Guidelines recommend surgery as the preferred treatment for thyroid carcinoma; this may, however, lead to complications such as recurrent laryngeal nerve injury and hypoparathyroidism [2]. Thermal ablation has, thus, been gaining popularity in the treatment of PTC due to its advantages of safety, effectiveness, and minimal invasiveness; it has become the current research hotspot of interventional therapy [3].

Although PTC is an inert cancer, 30%–80% of patients develop cervical lymph node metastases (CLNM) [4,5], a high risk factor for poor prognosis [6]. The Korean Society of Thyroid Radiology (KSThR) and European Thyroid Association (ETA) define lymph nodes (LNs) without suspicious imaging features (microcalcifications, cystic changes, hyperechogenicity, and abnormal vascularity) as indeterminate LNs [7,8]. Indeterminate LNs occur frequently in the neck of patients with thyroid cancer post-ablation, and their risk of malignancy is about 19.5%, much higher than that of benign LNs (2.8%) [9].

Ultrasound is the preferred method for examining LNs in thyroid carcinoma as it has high sensitivity and specificity for the diagnosis of suspicious LNs; however, the diagnosis of indeterminate LNs remains ambiguous [6]. One study combined microvascular imaging with power Doppler ultrasound to correctly identify 80.8%–90.1% of indeterminate LNs as benign or malignant based on LN vascularity [6]. Another study using contrast-enhanced ultrasound concluded that long-/short-axis ratio ≤1.5, peripheral or mixed blood flow, absence of hilar structure, centripetal or mass enhancement, and heterogeneous enhancement are high predictors for metastasis [10]. In addition, the combination of computed tomography and ultrasound can increase the diagnostic accuracy for indeterminate LNs by 16.4% [11]. Previous studies have involved a variety of examinations, but no uniform conclusions have been drawn. These studies simply focus on the ultrasound characteristics of the LN at a certain time point, and their patterns of change over time have rarely been reported. Moreover, previous studies explored indeterminate LNs before and after surgery; however, post-ablation changes have been rarely reported. Unlike conventional surgery, thermal ablation uses extremely high or low temperatures locally to induce irreversible cellular damage and, eventually, lead to apoptosis and coagulative necrosis of tumor cells, which can stimulate inflammatory and immune responses in the body and lead to reactive hyperplasia of LNs [12], which appear as indeterminate LNs on ultrasonogram. Therefore, the identification of indeterminate LNs after ablation was more complicated. Simultaneously, this highly sensitive population, which can be actively monitored for PTC yet opt for ablation, is under greater psychological stress from cervical indeterminate LNs than is the general population. In summary, the differential diagnosis and clinical management of benign and malignant indeterminate LNs are worthy of further study.

Therefore, this study investigated the predictors for metastasis and the variation pattern of the sonogram characteristics in cervical indeterminate LNs after PTC ablation by long-term ultrasound follow-up to provide meaningful guidance for the differential diagnosis of benign and malignant indeterminate LNs.

Materials and methods

Participants

This retrospective study was approved by the ethics committee of the General Hospital of the Chinese People’s Liberation Army, and written informed consent was obtained from the patients. Patients who underwent PTC ablation and had new cervical LNs after ablation at our hospital between January 2019 and January 2022 were selected. Some patients with tumors larger than 1 cm in diameter but who voluntarily opted for ablation were also included in this study (Figure 1). The exclusion criteria were: (1) preoperative presence of suspicious or indeterminate LNs; (2) incomplete clinical data; (3) history of other malignancies; (4) poor ultrasound image quality; and (5) history of neck surgery, radiotherapy, and chemotherapy (Protocol number: ChiCTR2200056848).

Figure 1. Patient selection process.

Evaluation of LNs

All patients underwent ultrasound examination of the neck using Resona R9 (Mindray), iU Elite (Philips Healthcare), SEQUOIA 512 (SIEMENS), or ACUSON S2000 (SIEMENS) scanners with a 7–12-MHz linear phased-array transducer. Patients were followed up with ultrasonography of the LNs at post-ablation months 1, 3, 6, and 12. Patients were placed in the supine position, and a full examination of the LNs in levels I to VII of the neck was performed, while representative gray-scale and color Doppler images of indeterminate LNs were taken. All examinations were performed by ultrasound physicians with more than 10 years of experience in thyroid ultrasound diagnosis.

Imaging analysis

The location, echogenicity, vascularity, and size of the LNs were evaluated during the follow-up. The vascularity was classified into four levels according to the distribution of blood flow within the LN: level 0, no flow signal; level 1, distributed in the center; level 2, distributed in the periphery; and level 3, both central and peripheral distribution. The diameters of the three dimensions of LN were recorded, and the volume was calculated using the equation [13]: $\mathrm{V}=\frac{\pi \mathit{abc}}{6}.$ (V is the volume, a is the largest diameter, and b and c are the other two perpendicular diameters). The KSThR and ETA guidelines classify LN as benign, indeterminate, and suspicious based on ultrasound features and risk of metastasis. Imaging features of suspicious lymph nodes include microcalcifications, cystic changes, hyperechogenicity, and abnormal vascularity. Benign LNs were defined as LNs without suspicious imaging features but with the typical imaging feature of benign LNs, including a central echogenic hilum or a central radiating hilar vascularity. Indeterminate LNs were defined as LNs without suspicious or benign LN imaging features but with eccentric, malformed, or absent hilum, independent of nodule shape [7,8]. In this study, the changes in LN volume and sonographic features at follow-up were compared with those at the initial review.

Statistical analysis

SPSS 21.0 software (IBM) was used for statistical analysis. Continuous variables are expressed as mean ± SD, and t-test or Mann-Whitney U test was used for comparison between groups. Classification variables were compared using the χ2 test or Fisher’s exact test. For follow-up data, generalized estimating equation (GEE) logistic regression models were used to assess the relationship between the malignancy status of lymph nodes and ultrasound characteristics of the nodes. The trend of non-CLNM and CLNM volume changes was tested by one-way analysis of variance. A p-value <0.05 was considered significant.

Results

Patient selection and grouping

We reviewed 556 patients with new cervical LNs after PTC ablation at our institution between January 2019 and January 2022. Following the inclusion and exclusion criteria, 138 LNs from 99 patients were included in our study. Among them, 90 were benign LNs and 48 were indeterminate LNs. Of the indeterminate LNs, there were 36 non-CLNM (75.00%) and 12 CLNM (25.00%) lesions (Figure 1). The final diagnosis of LNs was based on fine-needle aspiration cytology (FNAC) and ultrasound follow-up within one year. If both FNAC and ultrasound follow-up yielded negative results, LNs were regarded as non-CLNM.

Predictors of indeterminate LN

The basic clinical information and tumor characteristics of the patients are shown in Table 1. Unclear boundary, irregular shape, LN level, and post-ablation Hashimoto’s thyroiditis (HT) were significantly associated with indeterminate LNs (p = 0.046, p = 0.004, p = 0.000, and p = 0.040, respectively). Benign LNs were prone to developing at level III (32.8%), while indeterminate LNs were at level VI (64.9%). The remaining features were not significantly associated with indeterminate LNs (all p > 0.05).

Table 1. Basic clinical information and ultrasound features of patients with papillary thyroid carcinoma after ablation.

Group	Benign LN (n = 90)	Indeterminate LN (n = 48)	χ²/ t/z	p
Sex			0.257	0.612
Female	10	11
Male	42	36
Age(years)	43.08 ± 9.725	40.96 ± 10.837	0.715	0.400
Multifocality			0.243	0.622
Single	45	39
Multiple	7	8
Tumor location			4.126	0.127
Left lobe	24	31
Right lobe	31	25
Isthmic	5	1
Tumor location			0.539	0.764
Upper	15	15
Middle	18	20
Lower	27	22
Tumor size (cm)	0.7133 ± 0.3601	0.8088 ± 0.4748	−1.001	0.317
Tumor volume (mL)	0.2028 ± 0.3468	0.4628 ± 1.5829	−0.982	0.326
Unclear boundary			3.996	0.046
Present	47	35
Absent	13	22
Irregular shape			8.162	0.004
Present	42	25
Absent	18	32
Microcalcification			0.941	0.332
Present	37	40
Absent	23	17
Cystic change			0.000	1.000
Present	20	19
Absent	40	38
Vascularity			4.554	0.207
0	39	33
1	10	16
2	5	1
3	6	7
A/T			0.225	0.635
≤1	30	26
>1	30	31
Ablated number			0.011	0.915
Single	36	33
Multiple	16	14
Ablated volume	1.67 ± 1.63	1.91 ± 2.06	−1.020	0.308
Level			30.549	0.000
II	16	3
III	21	7
IV	8	16
VI	19	48
Hashimoto’s thyroiditis before ablation			1.468	0.226
Present	15	19
Absent	37	28
Hashimoto’s thyroiditis after ablation			4.223	0.040
Present	16	24
Absent	36	23

LN: lymph node.

Predictors of CLNM in indeterminate LN

The basic clinical information and tumor characteristics of the patients are shown in Table 2. Tumor volume and cystic change were associated with metastatic CLNM (p = 0.043 and p = 0.002, respectively). The remaining features were not significantly associated with CLNM (all p > 0.05).

Table 2. Basic clinical information and ultrasound features of patients with indeterminate lymph nodes for papillary thyroid carcinoma after ablation.

Group	Non-CLNM (n = 36)	CLNM (n = 12)	χ²/ t/z	p
Sex			1.345	0.256
Female	7	4
Male	29	7
Age(years)	40.11 ± 10.751	43.73 ± 11.163	0.001	0.972
Multifocality			0.639	0.659
Single	29	10
Multiple	7	1
Tumor location			0.566	0.754
Left lobe	23	8
Right lobe	20	5
Isthmic	1	0
Tumor location			0.217	0.897
Upper	11	4
Middle	17	5
Lower	16	4
Tumor size (cm)	0.7364 ± 0.3934	1.0538 ± 0.6424	3.936	0.052
Tumor volume (mL)	0.2106 ± 0.3512	1.3164 ± 3.1981	−2.026	0.043
Unclear boundary			0.000	0.991
Present	27	8
Absent	17	5
Irregular shape			0.199	0.665
Present	20	5
Absent	24	8
Microcalcification			0.007	0.932
Present	31	9
Absent	13	4
Cystic change			9.766	0.002
Present	10	9
Absent	34	4
Vascularity			5.534	0.137
0	27	6
1	13	3
2	1	0
3	3	4
A/T			0.002	0.965
≤1	20	6
>1	24	7
Ablated number			0.043	1.000
Single	25	8
Multiple	11	3
Ablated volume	1.66 ± 1.25	2.72 ± 3.63	−0.440	0.660
Level			4.364	0.225
II	2	0
III	0	1
IV	8	4
VI	26	7
Hashimoto’s thyroiditis before ablation			1.032	0.485
Present	16	3
Absent	20	8
Hashimoto’s thyroiditis after ablation			1.242	0.318
Present	20	4
Absent	16	4

CLNM：cervical lymph node metastasis.

Indeterminate LN's predictors variation pattern with time and diagnostic value

GEE analysis of the internal sonographic features of indeterminate LNs revealed statistically significant differences in microcalcifications, cystic changes, and vascularity when comparing CLNM and non-CLNM lesions (p = 0.004, p = 0.002, and p = 0.010, respectively). In CLNM, nine (75.00%) showed microcalcifications and seven (58.33%) showed cystic changes, while in non-CLNM, eleven (30.56%) showed microcalcifications and four (11.11%) showed cystic changes. Regarding changes in vascularity, four (33.33%) showed increased vascularity and one (8.33%) showed decreased vascularity in CLNM. Eight (22.22%) showed decreased vascularity, and two (5.56%) showed increased vascularity in non-CLNM. The rest of the CLNM and non-CLNM showed no clear changes in vascularity. Thus, most indeterminate LNs showed no clear change in vascularity during follow-up, and the residual CLNM vascularity elevated and transformed into peripheral and mixed patterns, while non-CLNM vascularity decreased and gradually converged to the central pattern. In addition, there was no statistically significant difference in the change of unclear boundary, irregular shape, loss of fatty hilum and hyperechogenicity at follow-up (all p > 0.05) (Table 3).

Table 3. GEE analysis of the internal ultrasound characteristics of indeterminate lymph nodes.

Predictor	B	standard error	OR (95% CI)	P
Unclear boundary	0.819	0.821	2.27 (0.45–11.33)	0.318
Irregular shape	−1.624	0.947	0.20 (0.03–1.26)	0.086
Microcalcification	2.362	0.815	10.61 (2.15–52.37)	0.004
Cystic change	3.149	1.016	23.32 (3.19–170.82)	0.002
Loss of fatty hilum	1.262	1.278	3.53 (0.29–43.27)	0.324
Hyperechogenicity	−2.052	1.779	0.13 (0.01–4.20)	0.249
Vascularity	0.617	0.2388	1.85 (1.16–2.96)	0.010

GEE：generalized estimating equation.

Table 4. Volume changes of indeterminate lymph nodes with time.

Month	Group	Non-CLNM	CLNM	χ²	P
	<−0.08	3	0
1-3	−0.08-0.12	11	12	6.087	0.048
	>0.12	4	0
	<−0.10	6	0
3-6	−0.10–0.10	14	3	1.900	0.387
	>0.1	2	1
	<−0.15	2	0
6-12	−0.15–0.00	7	2	0.590	0.744
	>0.00	3	1

CLNM：cervical lymph node metastasis.

Follow-up of cervical indeterminate LNs at 1, 3, 6 and 12 months after PTC ablation, the mean volumes of CLNM were 0.16, 0.18, 0.17, and 0.14 ml, respectively, which were not statistically significant (p = 0.779) (Figure 2). The mean volumes of non-CLNM were 0.21, 0.19, 0.12, and 0.11 ml, respectively, showing a gradual decrease with a statistically significant difference (P trend = 0.012)(Figure 3). Of note, the non-CLNM volume gradually decreased after ablation, while CLNM volume did not change. The volume changes in LNs at post-ablation months 1–3, 3–6, and 6–12 were grouped equidistantly. Among them, there was a statistically significant change in volume between CLNM and non-CLNM lesions at post-ablation months 1–3 (p = 0.048), with the highest diagnostic efficiency (52.2%) when the LN volume change was between −0.08 and 0.12 ml, while no statistically significant change in LN volume was seen in postoperative months 3–6 and 6–12 (p = 0.387 and p = 0.744, respectively) (Table 4, Figure 4). In LN follow-up, the sensitivity of microcalcifications and cystic changes was relatively high (75.0% and 88.9%, respectively), and the sensitivity and specificity of elevated vascularity was 80.0%. The sensitivity of LN volume changes between −0.08 and 0.12 ml was 100.0%, the negative predictive values were all at a high level, 89.3%, 86.5%, 88.9%, and 100.0%, respectively, and the areas under the curve of the first four were 0.708, 0.813, 0.800 and 0.621, respectively (Table 5).

Figure 2. Volume changes in CLNM in indeterminate lymph nodes after PTC thermal ablation (mL).

Figure 3. Volume changes in non-CLNM in indeterminate lymph nodes after PTC thermal ablation (mL).

Figure 4. Ultrasonogram of left cervical non-metastatic lymph node at VI level in a patient after PTC thermal ablation. A. Lymph node volume was 0.23 ml at the 1^st month after ablation; B. Lymph node volume was 0.14 ml at the 3^rd month after ablation; C. Lymph node volume was 0.06 ml at the 6^th month after ablation; D. Lymph node volume was 0.05 ml at the 12^th month after ablation. A gradual decrease is observed.

Table 5. Diagnostic value of ultrasonographic findings for predicting metastasis in indeterminate lymph nodes.

Predictor	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	Accuracy	χ²	P
Microcalcification	75.0	69.4	45.0	89.3	0.708	7.162	0.007
Cystic change	58.3	88.9	63.6	86.5	0.813	11.124	0.001
Elevated vascularity	80.0	80.0	66.7	88.9	0.800	4.667	0.031
Volume variation between −0.08-0.12 ml	100.0	35.3	52.2	100.0	0.621	5.156	0.002

NPV: negative predictive value; PPV: positive predictive value.

Discussion

In this study, unclear boundaries and irregular shapes were included as ultrasound features of tumors, and these were closely associated with indeterminate LNs. This is consistent with previous results and suggests these ultrasound features as important factors in predicting indeterminate LNs [14,15]. Furthermore, we concluded that indeterminate LNs were strongly associated with post-ablation HT. HT, the most common autoimmune disease of the thyroid, often causes LN enlargement due to a chronic inflammatory immune response [15]. The enlarged LNs caused by it are frequent in level VI, often show loss of fatty hilum and have a rounded morphology [16]; such LNs can also be called indeterminate LNs [7,8]. Furthermore, we concluded that the majority of indeterminate LNs occur in level VI. Therefore, after ablation, indeterminate LNs caused by HT should also undergo ultrasound for the diagnosis of potential CLNMs. Thus, the differential diagnosis of benign and malignant indeterminate LNs becomes more complicated.

We further analyzed the predictors of metastasis in indeterminate LNs and found that the larger the tumor volume, the higher the risk of malignancy in indeterminate LNs, while the maximum tumor diameter was not relevant. This is consistent with the conclusion of a related study by Park et al. [17] showing that tumor volume, rather than tumor size, is a significant predictor of malignant propensity in indeterminate LNs. It has been previously reported that tumor cystic change is an independent predictor of CLNM [18], and we demonstrated that it is also an important guide for the differential diagnosis of benign and malignant indeterminate LNs.

Long-term, multiple ultrasound follow-ups of indeterminate LNs after PTC ablation revealed the importance of microcalcifications, cystic changes, vascularity, and volume changes in differentiating CLNM from non-CLNM. In the progression of CLNM, liquefied necrosis, coagulative necrosis, hemorrhage, and calcium deposition due to the rapid proliferation of vascular and fibrous tissues occur within the LN due to infiltration of tumor cells [19], manifesting as microcalcifications and cystic changes on ultrasonogram. One study concluded that ≥5 microcalcifications and cystic changes are independent predictors for PTC CLNM [20,21]. Moreover, LN-responsive hyperplasia occurs owing to the stimulation of ablation, followed by the gradual self-healing of the organism, leading to calcium salt deposits and liquid dark areas in non-CLNM, which may be the cause of false positives [22,23]. Most previous studies were statistically analyzed at a single time point, yielding a sensitivity, specificity, and accuracy of 75.4%, 47.9%, and 0.610, respectively, for microcalcifications and of 25.8%, 99.6%, and 0.478, respectively, for cystic lesions when diagnosing CLNM [20,24]. In this study, the long-term follow-up of indeterminate LNs yielded a specificity of 69.4% for microcalcifications and a sensitivity of 58.3% for cystic changes, both with an accuracy of 0.708 and 0.813, respectively, for the diagnosis of CLNM. All were significantly higher compared to previous studies observed at a single time point.

In the early stage of micro-infiltration of tumors, there is less structural destruction within the LN, leading to a central radiating hilar vascularity. With increased infiltration of tumor cells, on the one hand, tumor blood vessels are formed in the intercellular space induced by VEGF-C. On the other hand, tumor infiltration blocks the blood supply to the hilum, resulting in the lymphoid tissue having to obtain blood supply from the tumor margin, causing the formation of marginal blood vessels. Increased marginal vascularity in CLNM is a well-known imaging feature and is widely used in clinical practice. But when the tumor infiltrates further and gradually replace the lymphatic tissue, the original blood vessels of the LN proliferate and form central vessels within the LN that are not clearly connected to the hilum [14,23,25,26]. Therefore, judging LN benignity and malignancy from vascularity at a single time point alone may lead to false negatives. The 2015 ATA guidelines suggest that abnormal vascularity as a single imaging feature is not sensitive enough [2]. In our study, the long-term observation of the vascularity of indeterminate LNs revealed that elevated vascularity is of great value in the diagnosis of CLNM, with a sensitivity, specificity and accuracy of 80.0% [24,27]. The diagnostic value of CLNM was improved compared to the previous diagnosis of CLNM by observing vascularity at a single time point, providing a novel direction for diagnosing cervical indeterminate LNs after PTC ablation by observing the vascularity of LNs.

LNs may show abnormal size and morphology in response to persistent inflammatory stimulation and appear as indeterminate on sonography [6], which may lead to false positives and affect the diagnosis and differentiation of CLNM. Chu et al. demonstrated that the presence of immune cell infiltration in the transition zone, untreated tumor tissue, and peripheral blood indicates that ablation activates overall immunity. Moreover, the mechanical cell damage caused by thermal ablation releases various immunogenic intracellular substrates such as DNA, RNA, heat shock proteins, and so on that activate innate immunity and stimulate acquired immune responses [12]. In addition, the destruction of ablated tissue, tumor cells, local extracellular matrix, and tissue components releases pro-inflammatory cytokines, causing aseptic inflammation [28,29]. In non-CLNM, lymphocyte proliferation within lymphoid follicles, expansion of lymphatic sinuses, and cortical thickening of lymph nodes are stimulated by a combination of the body’s immune and inflammatory responses, resulting in an increase in LN volume. Previous studies suggested that the kinetics of tissue response after ablation peaks between 72 h and 21 days and then gradually decreases [30,31]. In two studies of inflammatory markers after ablation with a 6-month follow-up, it was concluded that inflammatory markers began to increase from 18–24 h after the surgery and then gradually decreased [32,33]. Therefore, the ablation-induced immune response and inflammatory response stimulated the LN volume to increase; however, after 1 month, as the inflammatory response gradually diminished, the LN volume gradually decreased. Moreover, CLNM volume did not change definitively at the 1-year follow-up after ablation. Studies of post-surgical indeterminate LNs with regular monitoring have reached similar conclusions, with the majority (16/21) of CLNMs not changing definitively during 2–3 years of follow-up [34].

This study also concluded that LN volume changes between −0.08 and 0.12 ml at post-ablation months 1–3 had the highest diagnostic efficiency for CLNM, with an accuracy of 62.1%. Therefore, the 3^rd month after ablation becomes an important time point for review. If the LN volume change did not fluctuate within the aforementioned range at post-ablation month 3, it was more inclined to be benign, and its continued volume reduction at follow-up further corroborated the benign tendency of LN. Conversely, malignancy was considered. Because there are no clear suspicious imaging features of indeterminate LNs, the change in LN volume becomes an important and non-negligible index to determine their benignity and malignancy at the follow-up after ablation, providing meaningful guidance for the diagnosis of indeterminate LNs after PTC ablation.

There are some limitations to this study: On the one hand, the sample size of CLNM included is small. Since PTC is more inert, most patients who choose ablation have papillary thyroid microcarcinomas <1 cm in diameter, and their chance of developing CLNM is only 1%–2%[2]; thus, the sample size of CLNM included in this study is more in line with the incidence and metastasis rate of this disease. On the other hand. The immunological and pathological processes mentioned in the discussion were not derived from our own study. We will expand the sample size for further in-depth study.

In conclusion, for indeterminate LNs after PTC ablation, the month 3 is an important time point for review. By observing the changes in microcalcifications, cystic changes, vascularity, and LN volume, a reasonable judgment can be made on whether it is benign or malignant, providing meaningful guidance for clinical decisions.

Geolocation information

No. 28 Fuxing Road, Haidian District, Beijing, China.

Acknowledgment

None.

Disclosure statement

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.