The prognosis for PTC patients is generally favorable, with a low recurrence rate. However, conflicting studies exist regarding the impact of LNM on survival. Some suggest that PTC patients with LNM at initial surgery or experiencing LNM recurrence have a lower survival rate[17–20], while others find no significant effect[21, 22]. In most countries, routine lateral lymph node dissection (LLND) occurs only when clear evidence of LNM is present. Preventive lymphadenectomy is not recommended for patients without preoperatively detected cervical LNM. At our hospital, CLND is routinely performed for most PTC patients. LLND is only performed when LLNM is confirmed by preoperative or intraoperative pathological examination. Despite controversy over the prognostic significance of lymph node involvement at initial surgery, regional lymph node recurrence remains a concern[23, 24]. Considering patients’ quality of life, the presence of LNM plays a crucial role in mitigating subsequent surgical interventions.
Preoperative assessment of LNM in PTC relies on color Doppler ultrasound (US) and neck computerized tomography (CT). However, US sensitivity for detecting LNM is only 60–70%[25, 26], leading to challenges in distinguishing reactive lymphadenopathy from true metastatic disease. Enhanced CT scans can identify calcified metastatic nodes but have limitations in detecting non-calcified nodes[27]. Clinicians still struggle to determine the need for LND before PTC surgery.
Our study analyzed risk factors associated with CLNM, LLNM, and skip metastasis. We found that male gender, age < 45 years, MAD > 1 cm, BMI ≥ 28 kg/m², and multifocality correlated with CLNM. Interestingly, HT emerged as a protective factor for CLNM. Among these factors, male gender, age < 45 years, and MAD > 1cm emerged as independent risk factors. While previous studies also linked age < 45, male gender, tumor size, and multifocality to CLNM[28–30]. Some studies indicated HT as a risk factor for CLNM[28], but others suggested potential protective mechanisms of HT[31]. The specific impact of HT remains unclear. Our study showed a reduction in the risk of CLNM occurrence in HT patients. Close monitoring for CLNM is recommended in patients with these independent risk factors, considering preventive CLND.
The variables associated with the incidence of LLNM included age < 45 years, MAD > 1 cm, BMI ≥ 28 kg/m², multifocality, and CLNM. Meanwhile, MAD > 1 cm, multifocality, and CLNM established as independent risk factors for LLNM. This study also revealed that tumors situated in the upper pole exhibited a higher propensity for developing LLNM and skip metastasis, while those located in the lower pole were more likely to develop CLNM. A meta-analysis suggested that CLNM, tumor size, multifocality, male gender, and tumor location were independent risk factors for LLNM[32], which aligns with the results of this study. Zhao et al.[33] also identified a tumor diameter > 1 cm and CLNM as independent risk factors for LLNM, and found that upper pole tumors had a higher propensity for skip metastasis, consistent with our findings. Upper pole tumors are more likely to demonstrate skip metastasis, potentially due to preferential dissemination of the tumor via the superior thyroid artery to the lateral lymph nodes rather than through the lymphatic vessels[34].We recommend that PTC patients with preoperative examinations indicating tumor size > 1 cm, multiple lesions, or evident CLNM found intraoperatively, should be carefully evaluated for the potential presence of LLNM. These individuals may undergo lateral lymph node (LLN) biopsy during surgery, and if deemed necessary, LLND may be performed. For tumors located at the upper pole, even without apparent CLNM, monitoring of LLN should still be conducted.
Furthermore, BMI was a key variable of interest in this investigation. Given the observed higher incidence of LNM among obese patients in clinical practice, we conducted a comparison between obese patients (BMI ≥ 28 kg/m²) and non-obese patients (BMI < 28 kg/m²). Univariate analysis revealed that obese patients exhibited a greater likelihood of CLNM and LLNM compared to non-obese patients. However, multivariate analysis indicated that BMI did not independently contribute to the risk of LNM. The relationship between obesity and LNM remains ambiguous, with limited relevant studies vailable[35]. Inclusion of BMI in the analysis provided clinicians valuable insights.
Although numerous studies have investigated the risk factors for CLNM or LLNM, the conclusion is still controversial. Our study conducted a comprehensive statistical comparison of the risk factors associated with CLNM, LLNM, and skip metastasis, offering a more thorough analysis. LNM significantly contributes to postoperative recurrence and poor prognosis in patients with PTC, potentially necessitating secondary surgery and impacting patients' psychological well-being and quality of life. However, performing LND on all patients may increase the incidence of unnecessary surgical complications such as recurrent laryngeal nerve injury, hypoparathyroidism, and chylothorax. Consequently, preoperatively evaluating LNM and determining whether to perform LND has remained a challenging issue for surgeons. Some studies have indicated that prophylactic CLND can reduce local recurrence rates in high-risk patients[36, 37], while therapeutic LLND should be considered for those with suspected or confirmed LLNM preoperatively[14]. US and CT imaging have inherent limitations in distinguishing between different types of lymph nodes, and biopsy is not routinely performed as an examination method. When combined with an analysis of LNM risk factors, these imaging methods can enhance effectiveness and accuracy in evaluating lymph nodes, reducing the likelihood of misdiagnosis, ultimately diminishing the risk of recurrence, and enhancing patient quality of life.
Our study has certain limitations. Firstly, it is a retrospective study, and despite the large sample size, the results may be subject to bias. Secondly, there is a possibility of occult cancer or LNM that cannot be diagnosed through pathology. Thirdly, due to the limited number of skip metastasis cases, we did not conduct a multivariate analysis in this subgroup. Therefore, we hope that future research will involve a multi-center prospective study to more accurately analyze the risk factors for PTC patients.