Patterns, Predictive Factors, and Prognostic Impact of Contralateral Lateral Lymph Node Metastasis in N1b Papillary Thyroid Carcinoma

Although the incidence among patients with bilateral lateral lymph node metastasis (LLNM) in N1b papillary thyroid carcinoma (PTC) is reported to be as high as 40%, only a few reports have addressed the characteristics of contralateral LLNM. Therefore, this study aimed to investigate the characteristics of patients with contralateral LLNM in N1b PTC. This study retrospectively reviewed 834 patients with N1b PTC who underwent modified radical neck dissection between January 1997 and June 2015. Of the 834 N1b PTC patients, unilateral LLNM was found in 728 patients (87.3%) and bilateral LLNM in 106 patients (12.7%). The independent predictors of contralateral LLNM in N1b PTC patients were male sex (adjusted odds ratio [OR], 1.647; p = 0.039), tumor larger than 4 cm (adjusted OR, 6.700; p < 0.001), multiplicity (adjusted OR, 1.754; p = 0.040), bilobar involvement (adjusted OR, 1.971; p = 0.010), and bilateral central LN metastasis (CLNM) (adjusted OR, 2.829; p = 0.025). Moreover, contralateral LLNM significantly increased the risk of overall (adjusted hazard ratio [HR], 1.943; p = 0.016) and lateral neck (adjusted HR, 2.246; p = 0.015) locoregional recurrence. In the preoperative period, the meticulous evaluation of contralateral lateral neck may be required for male N1b PTC patients with tumor larger than 4 cm, multiplicity, bilobar involvement, and/or bilateral CLNM. In the postoperative period, N1b PTC patients may be re-stratified according to the contralateral LLNM, and meticulous follow-up assessment is required for N1b PTC patients with contralateral LLNM.