Determining the Minimum Number of Examined Lymph Nodes for N1b Papillary Thyroid Cancer Patients

Background: This study aimed to evaluate the correlation between the number of examined lymph nodes (eLNs) and postoperative residual lateral LN disease in patients with papillary thyroid cancer (PTC) and lateral nodal metastasis (N1b) and determine the minimal threshold for the eLNs. Methods: Patients diagnosed with unilateral N1b PTC who underwent total thyroidectomy with therapeutic LN dissection of the central and lateral compartments between January 2012 and December 2022 were included. Multivariate logistic regression analyses were performed to identify the threshold number of eLNs that independently influenced the risk of residual lateral LN disease. Results: Residual lateral LN disease was identified in 56 (5.4%) of 1042 T1-2 patients and 74 (12.3%) of 602 T3-4 patients. When analyzed as a continuous variable, the number of eLNs in the lateral neck was independently associated with a reduced risk of residual lateral LN disease in both T1-2 (OR: 0.93; 95% CI: 0.90-0.97; p < 0.001) and T3-4 patients (OR: 0.94; 95% CI: 0.91-0.97; p < 0.001). As a categorical variable, the risk of residual lateral LN disease continued to decrease significantly until the number of eLNs reached 34 in T1-2 patients and 46 in T3-4 patients. Conclusion: Comprehensive preoperative imaging for LN status and systematic compartmental dissection of the affected levels are critical in managing N1b PTC. To minimize the risk of residual lateral LN disease, the minimum recommended number of eLNs in the lateral neck is 34 for T1-2 patients and 46 for T3-4 patients.