Risk Factors for Clinically Negative Level II Cervical Lymph Node Metastasis in Papillary Thyroid Carcinoma

Objectives: Papillary thyroid carcinoma (PTC) frequently presents with cervical lymph node metastasis, even in small tumors, and lateral lymph node involvement serves as an important prognostic factor. Therapeutic lateral neck dissection is typically recommended when nodal metastasis is clinically evident, usually including levels II-V. However, the necessity of routine level II dissection in patients without clinical or radiologic evidence of level II involvement remains controversial, given its association with increased surgical morbidity, particularly injury to the spinal accessory nerve. Identifying reliable clinicopathological predictors of occult level II metastasis may enable more selective surgical approaches that minimize unnecessary dissection while preserving oncologic safety. Therefore, this study aimed to identify clinicopathological risk factors associated with occult level II lymph node metastasis in patients with PTC who have clinically positive lateral nodes but no clinical evidence of level II involvement. Methods: We retrospectively analyzed 1247 patients who underwent thyroidectomy for PTC between 2015 and 2022. Of these, 67 patients with clinically positive lateral lymph node metastasis and clinically negative Level II nodes who underwent therapeutic lateral neck dissection were included. Clinicopathological features were compared between patients with and without occult Level II metastasis. Univariate and multivariate logistic regression analyses were performed to identify independent risk factors. Results: Among the 67 patients analyzed, 24 (35.8%) had occult Level II metastasis. Compared to those without, patients with occult Level II metastasis had significantly larger primary tumors (2.18 ± 1.31 cm vs. 1.51 ± 1.02 cm, p = 0.024), a greater number of central lymph node metastases (5.88 ± 4.41 vs. 3.37 ± 2.66, p = 0.005), larger maximum size of metastatic central lymph node (1.44 ± 1.07 cm vs. 0.87 ± 0.48 cm, p = 0.004), and a higher number of metastatic lateral lymph nodes (7.63 ± 3.75 vs. 3.19 ± 2.21, p < 0.001). Multivariate analysis identified the number of metastatic lateral lymph node as the only independent predictor of occult Level II involvement (OR = 1.57, 95% CI: 1.213-2.044, p = 0.001). The final multivariate model demonstrated a Nagelkerke R² of 0.46. ROC curve analysis confirmed good predictive performance (AUC = 0.85), and the optimal cut-off value was ≥ 5 metastatic lateral lymph nodes. Conclusions: A substantial proportion of patients with clinically negative Level II nodes harbor occult metastasis. The number of metastatic lateral lymph nodes is an independent predictor of occult Level II involvement and may assist in tailoring the extent of lateral neck dissection in patients with PTC.