Clinical outcomes of lobectomy versus isthmusectomy for clinically node-negative solitary isthmic papillary thyroid microcarcinoma: a retrospective cohort study

Introduction

Thyroid cancer is the most common malignancy of the endocrine system, and its incidence has increased markedly in recent decades, rising by approximately 189% over the past thirty years (1). Papillary thyroid carcinoma (PTC) accounts for 80–85% of differentiated thyroid carcinomas (DTCs) and is associated with excellent long-term outcomes, with 10-year disease-specific survival rates exceeding 98% (2,3). In contrast, thyroid carcinomas originating from the thyroid isthmus are relatively uncommon because of the narrow anatomic structure of the isthmus, with a reported incidence ranging from 2.5% to 12.3% (4).

With the growing adoption of routine health screening and improvements in imaging techniques, thyroid cancers are increasingly diagnosed at earlier stages. Tumors arising in the isthmus are also being identified more frequently due to its superficial anatomical location anterior to the trachea, which facilitates detection by high-resolution ultrasonography (US). Given the indolent nature and favorable prognosis of most papillary thyroid microcarcinomas (PTMCs), the surgical approach to DTC has increasingly moved toward more conservative strategies that aim to reduce treatment-related morbidity while preserving oncological safety. The 2015 American Thyroid Association (ATA) guidelines recommend thyroid lobectomy as an appropriate surgical option for patients with low-risk DTC measuring ≤4 cm without evidence of extrathyroidal extension (ETE) or lymph node metastasis (5). However, these recommendations primarily focus on tumors located within the lobes and provide limited guidance regarding tumors arising in the isthmus. As a result, the optimal surgical extent for isthmic papillary thyroid carcinoma (iPTC), particularly papillary thyroid microcarcinoma located in the isthmus (iPTMC), remains uncertain. More recently, the 2025 ATA guidelines have further emphasized the principles of individualized management and de-escalation of treatment for patients with low-risk DTC (6). In selected patients, active surveillance or minimally invasive treatments may even be considered (7). Although treatment strategies for DTC have become increasingly conservative, surgical resection remains the primary and most effective treatment for thyroid malignancies (8,9). Within this evolving paradigm, determining whether less extensive surgical approaches can achieve comparable oncological outcomes while reducing surgical morbidity has become an increasingly important clinical question.

Traditionally, total thyroidectomy was considered the standard surgical approach for iPTC because of the unique anatomical characteristics of the thyroid isthmus. This anatomical vulnerability may facilitate ETE and central lymph node metastasis (CLNM). For patients with iPTMC without aggressive features, total thyroidectomy may represent overtreatment because of its higher risk of complications. Consequently, more conservative surgical procedures, including isthmusectomy (IT) and lobectomy (LT), have been proposed as potential alternatives (10-13). These approaches may provide benefits, including less surgical trauma and better preservation of thyroid function. However, current evidence comparing these two approaches remains limited, and the criteria for selecting the most appropriate surgical strategy for iPTMC have not been well established. Furthermore, the necessity and extent of prophylactic central lymph nodes (CLNs) dissection in iPTMC, including whether unilateral or bilateral dissection should be performed, remain controversial.

Ideally, these questions should be addressed through prospective randomized controlled trials. However, the indolent natural history and low event rates of iPTMC render such trials challenging to conduct. Consequently, well-designed retrospective studies remain a crucial source of evidence. For these issues, large-sample clinical data analyses remain limited, and further evidence is needed to clarify the optimal surgical strategy for iPTMC. Therefore, the present study aimed to assess the clinicopathologic characteristics, oncological outcomes, and surgical results of IT and LT for cN0 solitary iPTMC, providing additional evidence to guide surgical decision-making toward more personalized and conservative management. We present this article in accordance with the STROBE reporting checklist (available at https://gs.amegroups.com/article/view/10.21037/gs-2026-1-0046/rc).

Methods

Patients

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Clinical Research Ethics Committee at The First Affiliated Hospital, College of Medicine, Zhejiang University (No. 2025B-No.1444). Due to the study’s retrospective design, the Clinical Research Ethics Committee waived the necessity of obtaining written informed consent from participants. PTMC cases treated with thyroid surgery between January 2017 and January 2024 at the Department of Thyroid Surgery, The First Affiliated Hospital, College of Medicine, Zhejiang University, were retrospectively reviewed. The inclusion criteria for iPTMC were defined as follows: tumor size <1 cm, with the tumor center located between two imaginary lines perpendicular to the skin surface extending from the most lateral borders of the trachea. Patients whose tumors crossed the tracheal midline were excluded (Figure 1A). Accordingly, in all included cases, tumor margins were confined to one side without involvement of the tracheal midline (Figure 1B).

Figure 1 Schematic illustration of the definition of iPTMC and the inclusion/exclusion criteria of the study. iPTMC was defined as a tumor <1 cm in size with its center located between two imaginary lines drawn perpendicular to the skin surface from the most lateral points of the trachea. Tumors crossing or contacting the tracheal midline were excluded (A), whereas included tumors had margins confined to one side without tracheal midline contact (B). iPTMC, isthmic papillary thyroid microcarcinoma; LL, left lobe; RL, right lobe.

A total of 303 patients with cN0 solitary iPTMC were identified, including 96 (31.7%) who underwent IT with bilateral CLN dissection and 207 (68.3%) who received LT with unilateral CLN dissection. All patients met the ATA criteria for low recurrence risk, defined by the absence of central or lateral lymph node metastasis, multifocal disease, and distant metastasis on preoperative evaluation. All procedures were performed by the same surgeons (Y.J.W. and X.J.X.).

Data collection

In this retrospective study, we analyzed retrospectively collected data, including age, sex, and type of operation. The postoperative dataset included pathological tumor size, tumor location, CLNM, the number of metastatic and dissected CLNs, distant metastasis, microscopic extrathyroidal extension (mETE), as well as complications (transient and permanent hypocalcemia, hoarseness, hematoma, and lymphatic fistula), operative time, levothyroxine dosage, recurrence, and newly detected lesions on surveillance US.

Exclusion criteria

Patients were excluded if any of the following criteria were met: (I) gross extrathyroidal extension (gETE); (II) multifocal PTC; (III) central or lateral lymph node metastasis; (IV) non-PTC thyroid malignancy; (V) prior neck irradiation or a family history of thyroid cancer; (VI) previous thyroid surgery; or (VII) incomplete clinical records. Preoperative laryngoscopy was routinely performed in all patients. Permanent recurrent laryngeal nerve palsy was defined as vocal cord dysfunction lasting longer than six months after surgery.

Determination of surgical strategy

The surgical approach was determined through surgeon–patient consultation. Total thyroidectomy was performed in cases with gETE identified either preoperatively or intraoperatively. For patients with cN0 solitary iPTMC without gETE, treatment decisions were made using a shared decision-making (SDM) model, whereby clinicians and patients jointly evaluated the clinical condition and selected the most appropriate surgical strategy (14,15). Surgeons discussed the preoperative findings and individualized risk profiles, emphasizing that although these tumors were classified as low-risk according to ATA guidelines, the optimal extent of surgery remains controversial. Total thyroidectomy with bilateral CLN dissection carries higher risks and necessitates lifelong hormone replacement, whereas IT or LT may represent suitable alternatives with comparable oncological outcomes in appropriately selected cases.

Patients were counseled regarding potential trade-offs, including the risk of recurrence associated with IT and LT, as well as the possibility that LT may reduce the required dose of levothyroxine but does not eliminate surgical complications. Following this discussion, patients participated in the SDM process and chose their preferred surgical approach. Clinicopathologic features, postoperative complications, and recurrence outcomes were subsequently compared between the two groups.

Surgical techniques

IT group: thyroid resection was limited to tissue above a horizontal plane located 0.5 cm deep from the anterior surface of the trachea, with bilateral CLN dissection (Figure 2A).

Figure 2 Schematic illustration of isthmusectomy and lobectomy of the thyroid. (A) IT group: the thyroid tissue located above the horizontal plane at a depth of 0.5 cm from the anterior surface of the trachea was resected. (B) LT group: one thyroid lobe along with the isthmus was resected. The gray shaded area represents the extent of surgical resection. IT group, isthmusectomy group; LT group, lobectomy group.

LT group: the thyroid was accessed through a standard Kocher incision along the cervical linea alba, followed by removal of one lobe together with the isthmus and unilateral CLN dissection (Figure 2B).

Follow-up

Patients were followed at 3–6-month intervals, with US, thyroid function testing, and assessment of parathyroid hormone and serum calcium levels. Transient hypocalcemia was defined by serum calcium <2.11 mmol/L with parathyroid hormone (PTH) <15 pg/mL, whereas permanent hypocalcemia referred to hypoparathyroidism lasting longer than 6 months and requiring ongoing calcium and calcitriol supplementation. Thyroid-stimulating hormone (TSH) suppression therapy was administered during the first postoperative year, with target levels of 0.1–0.5 mU/L, followed by 0.5–2.0 mU/L thereafter. Routine follow-up included physical examination, neck US of the thyroid and central/lateral cervical lymph nodes, and thyroid function tests. Serum thyroglobulin monitoring was not utilized as a marker for recurrence, as its clinical utility is limited in patients with residual thyroid tissue. If suspicious lesions or lymph nodes were identified on US, contrast-enhanced neck computed tomography and fine-needle aspiration biopsy (FNAB) were performed. Recurrence was strictly defined as the presence of malignant cells confirmed by FNAB that necessitated secondary surgical intervention, with subsequent histopathological confirmation of PTC.

Statistical analysis

Patients were stratified into IT and LT groups. Statistical analyses were conducted using SPSS version 22.0. Continuous data are presented as mean ± standard deviation (SD), while categorical variables were compared using the Chi-squared or Fisher’s exact test, as appropriate. Between-group differences in continuous variables were evaluated using Student’s t-test or one-way analysis of variance (ANOVA). Non-normally distributed data are reported as median (interquartile range, IQR) and compared using the Mann-Whitney U test. Multivariable Cox regression was conducted to identify independent prognostic factors. Recurrence-free survival (RFS) was estimated using the Kaplan-Meier method, and group differences were compared using the log-rank test. Standardized mean differences (SMDs) were calculated to assess group balance, with values <0.2 indicating acceptable comparability. Statistical significance was defined as a two-sided P value <0.05.

Propensity score matching (PSM) was performed using the 1:2 nearest-neighbor method in consultation with biostatisticians. The model was adjusted for the following five variables: gender, age, CLNM, tumor size and mETE. Before matching, the mean propensity score was 0.321 for patients in the IT group and 0.315 for patients in the LT group. The majority of patients in the IT group were successfully matched to two patients in the LT group, although some were matched to fewer patients, depending on their scores. A total of 146 patients in the LT group were matched. After matching, the mean propensity score was 0.317 for patients in the IT group (n=85) and 0.317 for patients in the LT group (n=146). Post-matching balance was verified by SMDs. All statistical analyses were conducted using SPSS (version 22.0; IBM Corp., Armonk, NY, USA) and R (version 3.6.1; R Foundation, Vienna, Austria), with a significance threshold of P<0.05.

Results

Baseline characteristics of the patient

A total of 303 patients were analyzed, with a mean age of 43.35±11.94 years (range, 15–72 years) and a male-to-female ratio of 1:2.33. The median tumor size was 0.6 cm (IQR, 0.4–0.7 cm), and tumors >5 mm were observed in 49.8% of cases. Although no CLNM was identified preoperatively, postoperative pathology revealed metastasis in 94 patients (31.0%). The median number of dissected CLNs was 4 (IQR, 3.0–6.0), while the median number of metastatic nodes was 0 (IQR, 0.0–1.0), corresponding to a median CLNM ratio of 0 (IQR, 0.0–0.2). mETE was identified in 90 cases (29.7%). Regarding surgical management, 96 patients (31.7%) underwent isthmusectomy, while 207 patients (68.3%) received LT (Table 1).

Demographics and baseline characteristics before and after PSM

Clinicopathologic characteristics of the IT and LT groups were summarized in Table 2. Before matching, baseline variables were comparable between the two groups, including age, sex, tumor size, CLNM, mETE, and the number of metastatic CLNs (P=0.69, P=0.75, P=0.34, P=0.84, P=0.83, and P=0.72, respectively). The number of dissected CLNs was significantly higher in the IT group than in the LT group [6 (IQR, 4.0–9.0) vs. 4 (IQR, 3.0–5.0), P<0.001]. PSM was subsequently performed at a 1:2 ratio with a caliper width of 0.01, yielding 85 patients in the IT group and 146 in the LT group. After matching, baseline characteristics remained well balanced between the groups, including age, sex, tumor size, CLNM, mETE, and the number of metastatic CLNs (P=0.75, P=0.49, P=0.97, P=0.23, P=0.76 and P=0.57, respectively). The median number of dissected CLNs remained significantly higher in the IT group than in the LT group after matching [6 (IQR, 4.0–9.5) vs. 4 (IQR, 3.0–5.0), P<0.001]. This discrepancy may be attributable to the fact that IT involves routine bilateral CLN dissection, leading to a higher lymph node yield. The LT group had a significantly longer median follow-up duration than the IT group [41.0 (IQR, 28.0–54.0) vs. 24.5 (IQR, 15.3–31.8) months, P<0.001], and no cases of distant metastasis or disease-specific mortality were observed in either group during follow-up.

Comparison of surgery-related outcomes between the IT and LT groups

Surgical outcomes varied between the two groups (Table 3). Transient hoarseness was observed in 5.8% of patients in the LT group, whereas no cases were noted in the IT group (P=0.01). Temporary hypocalcemia developed in 5 patients (2.4%) following LT but was not observed after IT (P=0.18). No instances of permanent hypocalcemia, hematoma, or lymphatic fistula occurred in either group. The IT group showed a shorter operative duration than the LT group [56 (IQR, 51.0–59.0) vs. 59 (IQR, 56.0–68.0) minutes; P<0.001]. Despite universal postoperative TSH suppression therapy, patients in the IT group required lower doses of levothyroxine [43.8 (IQR, 43.8–50.0) vs. 56.3 (IQR, 50.0–65.8) µg; P<0.001].

Postoperative tumor recurrence

The median duration of follow-up was markedly more extended in the LT group compared to the IT group [41.0 (IQR, 28.0–54.0) vs. 24.5 (IQR, 15.3–31.8) months, P<0.001]. During the follow-up, 11 patients (3.6%) developed recurrence, with a mean recurrence time of 27.8±10.4 months (range, 15–48 months). Specifically, recurrence rates were 4.2% for IT and 3.4% for LT, representing no statistical disparity (P=0.73) (Table 2). In the matched group, recurrence occurred in 4 cases (4.7%) in the IT group and 5 cases (3.4%) in the LT group. A comparative analysis between patients with (n=11) and without (n=292) recurrence identified significant differences in median tumor size, CLNM, the count of metastatic CLNs, and the CLNM ratio (P=0.01, P<0.001, P<0.001, P=0.14, and P<0.001, respectively) (Table 4). Ultimately, no significant correlation was identified between IT and recurrence (P=0.75).

Multivariate analysis predicting RFS

Kaplan-Meier analysis with the log-rank test was performed to predict prognosis. There was no significant difference in RFS between the IT and LT groups before (Figure 3A) and after (Figure 3B) PSM (P=0.12 and P=0.10, respectively). To evaluate the IT and LT groups, Kaplan-Meier survival curves were generated based on several variables, including age (55 years), tumor size (0.5 cm), mETE, and CLNM (Figure 4). In the IT group, RFS did not differ significantly by age (<55 vs. ≥55 years, P=0.32) (Figure 4A), tumor size (<0.5 vs. ≥0.5 cm, P=0.76) (Figure 4C), and mETE (P=0.95) (Figure 4G). In the LT group, age (P=0.23) (Figure 4B) and mETE (P=0.13) (Figure 4H) were not associated with RFS. A statistically significant association between CLNM and RFS was identified in both groups (P=0.02 and P<0.001, respectively) (Figure 4E,4F). Notably, tumor size ≥0.5 cm was significantly associated with reduced RFS (P=0.02) in the LT group (Figure 4D).

Figure 3 Recurrence-free survival curves in the isthmusectomy and lobectomy groups before (A) and after (B) PSM. PSM, propensity score matching.

Figure 4 RFS curves comparing patients aged ≥55 and <55 years in the isthmusectomy group (A) and lobectomy group (B); RFS curves comparing patients with tumor size >0.5 and ≤0.5 cm in the isthmusectomy group (C) and lobectomy group (D); RFS curves comparing patients with and without central lymph node metastasis [CLNM(+) vs. CLNM(−)] in the isthmusectomy group (E) and lobectomy group (F); RFS curves comparing patients with and without microscopic extrathyroidal extension [microscopic ETE(+) vs. microscopic ETE(−)] in the isthmusectomy group (G) and lobectomy group (H). The Kaplan-Meier method and log-rank test were used for statistical comparisons. CLNM, central lymph node metastasis; ETE, extrathyroidal extension; RFS, recurrence-free survival.

Univariate analysis revealed that CLNM significantly associated with poor RFS (HR =21.665, 95% CI: 2.772–169.335; P=0.003). Multivariate analysis indicated that CLNM was independent prognostic factor for poor RFS (HR =19.720, 95% CI: 2.243–173.352; P=0.007) (Table 5).

Discussion

With the expansion of routine health screenings and advancements in diagnostic imaging, thyroid cancers are now being detected at increasingly earlier stages (16). Consequently, given the predominantly indolent behavior and excellent prognosis of DTC, a paradigm shift has emerged in their surgical management (17). According to the 2015 ATA guidelines, unless high-risk factors for recurrence are present, LT may be performed for solitary thyroid cancer smaller than 4 cm (5). The 2025 ATA guidelines indicated that in selected low-risk patients, active surveillance or minimally invasive treatments like radiofrequency ablation may be appropriate (6). Nevertheless, thyroid surgery remains the preferred treatment for most differentiated thyroid cancers. However, the guidelines have not specified the method and scope of surgery for thyroid cancer in the isthmus. The controversy surrounding the optimal surgical approach for iPTC stems from limited evidence and the unique anatomy of the isthmus, with the debate primarily focused on the appropriate extent of primary tumor resection and lymph node dissection (18,19).

Total thyroidectomy, with or without bilateral central neck dissection, has conventionally been the surgical approach of choice for many surgeons, owing to the more aggressive features of iPTC. The thin anatomy of the thyroid isthmus predisposes larger tumors in this region to capsular penetration, invasion of adjacent structures such as the anterior cervical muscles and trachea, and higher rates of lymph node metastasis and multifocality. According to a meta-analysis by Lyu et al., the rates of CLNM and ETE were 52.7% and 50.2%, respectively (20). Lee et al. reported CLNM and ETE rates of 71.4% and 100%, and Hahn et al. similarly noted higher corresponding rates of 68.8% and 83.3%, respectively (21,22). The findings of our study support the aggressive oncologic behavior of iPTC. Although all patients were cN0 based on careful preoperative examinations, postoperative pathology confirmed CLNM and mETE in 94 (31.0%) and 90 (29.7%) patients, respectively. However, total thyroidectomy inherently increases the risk of complications such as hypoparathyroidism and recurrent laryngeal nerve injury, thereby diminishing patients’ quality of life. Accordingly, controversy has emerged regarding whether more conservative surgical approaches, including IT or LT, can serve as reliable treatment options for iPTC (13,23). Wang et al. suggested that LT with ipsilateral CLN dissection may be appropriate for patients with paracentral iPTC without prelaryngeal or pretracheal lymph node metastasis (10). In addition, Yuan et al. reported that wide-field IT may represent an adequate treatment for selected patients with PTC confined to the isthmus (24). Evidence indicates that isthmusectomy or lobectomy may ensure oncological safety through tissue preservation. Consequently, these procedures reduce the incidence of postoperative adverse events and the requirement for hormone supplementation, ultimately optimizing the quality of life.

Previous studies have mainly evaluated the outcomes of different surgical approaches in the treatment of thyroid isthmus carcinoma. Comparisons have primarily focused on total thyroidectomy versus isthmusectomy, and total thyroidectomy versus LT. However, data directly comparing the outcomes of IT and LT are limited. According to Park et al., the 10-year recurrence rates were statistically comparable between the IT group (7.0%) and the total thyroidectomy group (5.4%) (25). No notable disparities in clinical success were identified by Gui et al. when comparing three types of thyroid surgery among 70 individuals diagnosed with iPTC (26). In the study by Lee et al., 89 patients underwent total thyroidectomy, 30 underwent LT, and 226 underwent isthmusectomy, with total thyroidectomy and LT combined for comparison with IT, without a separate evaluation of LT versus IT (12). Gong et al. performed a meta-analysis of 413 patients undergoing total thyroidectomy versus 401 patients undergoing less-than-total thyroidectomy (including IT and LT) for iPTC, but did not specifically compare IT with LT (13). Although these studies provide valuable initial evidence, the available data remain limited regarding the optimal choice between IT and LT for selected patients with iPTC.

Our study seeks to contribute to this ongoing debate by examining outcomes following IT and LT in a relatively large cohort. According to the 2015 ATA guidelines, this study included patients with cN0 solitary iPTMC, while excluding those with multifocal disease, gETE, and distant metastasis (5). This selection strategy was intended to focus on a lower-risk population of PTMC. Limiting the analysis to cN0 solitary iPTMC was intended to reduce confounding factors related to surgical extent when evaluating postoperative oncologic outcomes. In addition, patients with iPTMC crossing the tracheal midline were excluded, with inclusion limited to paracentral isthmus tumors whose margins did not contact the tracheal midline, in an effort to minimize potential bias in surgical decision-making. Our results revealed no significant divergence in RFS between the two surgical groups (IT vs. LT) based on Kaplan-Meier estimates, a finding that remained consistent both before and after PSM (P=0.12 and P=0.10, respectively), indicating that the oncologic outcomes of the two surgical approaches appear similar. Among patients undergoing isthmusectomy, no significant difference in RFS was observed between tumors ≤0.5 cm and those >0.5 cm, indicating that tumor size stratification may not substantially influence outcomes in this setting. In contrast, in the LT group, patients with tumors ≤0.5 cm tended to have more favorable RFS than those with larger tumors. These observations suggest that IT may provide similar oncologic outcomes across tumor size categories, whereas LT may represent a reasonable option for selected iPTMC patients with tumors ≤0.5 cm.

Beyond oncologic outcomes, surgical complications represent an important consideration in the selection of surgical extent. When comparable oncologic results can be achieved, choosing a procedure associated with fewer complications may contribute to improved postoperative quality of life. By avoiding the dissection of the tracheoesophageal groove and Berry’s ligament to protect the recurrent laryngeal nerve and parathyroid glands, IT presents significant anatomical advantages over LT (24). The resulting preservation of thyroid function also decreases the need for postoperative levothyroxine. In the current study, the IT group reported zero complications regarding hoarseness and hypocalcemia, whereas the LT group had rates of 5.8% (hoarseness) and 2.4% (transient hypocalcemia). Additionally, the IT group benefited from a shorter median surgical time and reduced hormone supplementation needs. Collectively, these data suggest that IT is safer and more effective at preserving thyroid function than LT.

Preoperative identification of ETE serves as a dependable prognostic indicator for disease advancement. In the 8th edition of the American Joint Committee on Cancer staging system, ETE is incorporated into the TNM stage and can influence treatment decisions (27). In this study, patients with gETE identified preoperatively or intraoperatively were excluded. However, postoperative pathology still revealed mETE in 55.2% of patients in the IT group and 56.5% in the LT group. These findings are consistent with the relatively aggressive oncologic behavior of iPTMC. According to the ATA guidelines, initial TSH suppression to 0.1–0.5 mU/L is recommended for intermediate-risk thyroid cancer patients, whereas low-risk patients may maintain TSH levels within the lower to mid reference range (0.5–2 mU/L). In this study, all patients received TSH suppression therapy during the first postoperative year, which means that some low-risk patients also underwent TSH suppression. Although all patients were categorized as low- to intermediate-risk, certain pathological features suggested a non-negligible risk of recurrence, and previous studies have indicated that iPTMC may carry a higher recurrence risk than tumors located in the thyroid lobes. This suggests that TSH suppression for some low-risk patients may have been somewhat more intensive than required, likely reflecting a center-specific management strategy rather than a universally applied approach in accordance with guidelines.

For most small-sized and noninvasive PTCs without clinical node involvement (cN0), the 2025 ATA guidelines do not support prophylactic CLN dissection, nor is it viewed as a widely adopted standard of practice (6). Routine surgical management at our center for thyroid cancer involves performing either ipsilateral or bilateral prophylactic CLN dissection. This clinical strategy aims to improve the precision of tumor staging, eliminate potential occult CLNM, and lower the incidence of persistent or recurrent disease, thereby mitigating the diagnostic limitations of preoperative imaging. Identifying CLNM preoperatively remains a significant challenge due to the small dimensions of the nodes and their anatomical obscuration by surrounding structures. Indeed, Alabousi et al. reported that the sensitivity of preoperative ultrasound is as low as 28% (28). Occult CLNM was detected in 31.0% of our iPTMC cohort during postoperative histological evaluation, a result that aligns with the aforementioned findings. The IT group underwent bilateral CLN dissection and had a significantly higher median number of dissected CLNs than the LT group. However, no significant difference was observed in the median number of metastatic CLNs between the two groups. Moreover, the median number of metastatic CLNs was significantly associated with recurrence. Comparative analysis revealed that the median count of metastatic CLNs was markedly higher in the recurrence cohort than in the non-recurrence cohort. Furthermore, Kaplan-Meier survival curves established that CLNM was an influential predictor of recurrence for both the IT and LT groups.

There are several limitations in this study. First, although PSM was performed to balance baseline characteristics, the retrospective design and limited sample size may have resulted in residual confounding. Moreover, no formal a priori sample size calculation was performed, and the low event rate of recurrence may limit the statistical power to detect small but clinically meaningful differences. In addition, surgical decisions in the IT and LT groups were made by patients after consultation, potentially introducing selection bias due to patients’ limited medical knowledge and preference for conservative surgery. Second, variability in the extent of CLN dissection represents another limitation. In the IT group, bilateral CLN dissection was routinely performed, whereas dissection in the LT group was more limited. This difference may affect the comparability of lymph node–related outcomes between groups. Although the number of dissected CLNs was used as a surrogate marker for dissection extent, it may not fully reflect the completeness of nodal clearance. Third, because PTMC is generally characterized by an indolent progression, the median follow-up times of 24.5 months (IT group) and 41.0 months (LT group) might be insufficient to document the full spectrum of disease recurrence. The difference in follow-up duration between the two groups may have influenced the assessment of oncologic outcomes. Therefore, the oncological equivalence between IT and LT observed in this study should be interpreted with caution. Finally, our study’s findings are subject to the constraints of a retrospective, mono-centric design, which might limit their broader applicability. Consequently, further verification through multi-center prospective randomized studies with expanded cohorts and prolonged monitoring is essential.

Conclusions

In conclusion, considering the relatively high incidence of occult CLNM and its potential association with recurrence in iPTMC, the role of prophylactic central lymph node dissection warrants careful clinical consideration. In this retrospective cohort, isthmusectomy was associated with preservation of thyroid function and potentially fewer postoperative requirements for levothyroxine, while demonstrating comparable oncological outcomes to lobectomy. However, given the retrospective design, potential selection bias, and limited follow-up, these findings should be interpreted with caution and regarded as preliminary. For selected patients, particularly those with tumors ≤0.5 cm in size, lobectomy may remain an appropriate surgical option.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://gs.amegroups.com/article/view/10.21037/gs-2026-1-0046/rc

Data Sharing Statement: Available at https://gs.amegroups.com/article/view/10.21037/gs-2026-1-0046/dss

Peer Review File: Available at https://gs.amegroups.com/article/view/10.21037/gs-2026-1-0046/prf

Funding: This study was supported by Zhejiang Medical Science and Technology Projects (No. 2022KY786).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://gs.amegroups.com/article/view/10.21037/gs-2026-1-0046/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Clinical Research Ethics Committee at The First Affiliated Hospital, College of Medicine, Zhejiang University (No. 2025B-No.1444). Due to the study’s retrospective design, the Clinical Research Ethics Committee waived the necessity of obtaining written informed consent from participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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