Effect of Tumor Location on the Risk of Bilateral Central Lymph Node Metastasis in Unilateral 1-4 cm Papillary Thyroid Carcinoma

Purpose: Papillary thyroid carcinoma (PTC) has a high incidence of lymph node metastasis (LNM). Our aim was to determine whether tumor location is a useful feature to predict bilateral central lymph node metastasis (CLNM) in unilateral 1-4 cm PTC. Patients and Methods: Data on unilateral 1-4 cm PTC patients from 2016 to 2019 were collected retrospectively. The clinical and pathological characteristics of the tumors and lymph nodes were analyzed statistically. Results: The mean patient age was 49.1 +/- 12.3 (23-73) years, and the majority were women (n=1334, 75.4%). A total of 1767 patients were analyzed, and 256 (14.5%) had bilateral CLNM. Tumor location was an independent risk factor in predicting bilateral CLNM (p<0.001). The odds of bilateral CLNM were the highest in the near isthmus (OR 6.452, 95% CI: 3.658-11.379, p<0.001). In a multivariate regression model adjusting for other risk factors, near-isthmus tumors had the highest risk of bilateral CLNM (OR 7.319, 95% CI: 3.844-13.933, p<0.001), followed by lower lobe tumors (OR 2.338, 95% CI: 1.315-4.155, p=0.004) and middle lobe tumors (OR 1.845, 95% CI: 1.035-3.291, p=0.038), compared to upper lobe tumors. Conclusion: Tumor location is an independent risk factor in predicting the risk of bilateral CLNM. Near-isthmus tumors carry the highest risk of bilateral CLNM.