Abstract: Background and purpose: Pathological lymph node metastasis (LNM) is not rare in clinical lymph node negative (cN₀) papillary thyroid carcinoma (PTC). The aim of this study was to investigate the risk factors of LNM, especially of high volume LNM (more than 5 metastatic lymph nodes) and contralateral central compartment LNM, in cN₀ PTC. Methods: Medical records of 350 PTC patients (265 female, 85 male, 212 patients with solitary lesion in unilateral lobe) were reviewed. All operations of these patients were performed by one surgical team. The clinical pathological data were collected, and univariate and multivariate analysis was performed. Results: LNM was confirmed in 138 patients (39.4%) and 20 patients had high volume LNM. In 169 patients with solitary lesion in unilateral lobe with total thyroidectomy and bilateral central neck dissection, 24 patients had contralateral metastasis (14.2%). In univariate analysis, tumor size (58.5% in >1 cm vs 33.6% in ≤1 cm) and tumor with calcification in preoperational ultrasonography (43.7% with vs 31.7% without) showed significant difference in prevelance of LNM. In multivariate analysis, tumor size >1 cm (OR=2.792) was the independent risk factor of LNM. Gender (3.8% in male vs 11.8% in female), age (10.7% <40 years vs 3.4% ≥40 years ), tumor size(13.4% in >1 cm vs 3.4% in ≤1 cm) and tumor with low echo in preoperational ultrasonography (13.9% with vs 4.8% without) showed significant difference in univariate analysis of high volume LNM. Male (OR=5.152), tumor size >1 cm (OR=5.712) and age <40 years (OR=3.959) were confirmed as independent risk factors of high volume LNM. Male (OR=3.105) and tumor size >1 cm (OR=3.863) were also demonstrated as independent risk factors of contralateral LNM in patients with solitary lesion in unilateral lobe, the prevalence of LNM were 26.5% in male and 26.1% in tumor size >1 cm, respectively. Conclusion: LNM was not “rare” in cN₀ PTC patients. Prophylactic central neck dissection should be performed in cN₀ patients with tumor size >1 cm. For cN₀ microcarcinoma, more active surgical treatment may be considered in male and young patients.

Key words: Papillary thyroid carcinoma, Clinical lymph node negative, Lymph node metastasis, Risk factor