Factors Influencing Central Neck Lymph Node Metastasis in Patients with Papillary Thyroid Microcarcinoma

Purpose: A papillary thyroid microcarcinoma (PTMC) measures 1 cm or less in diameter. The diagnosis, and thus the apparent incidence, of PTMC has recently increased owing to an increase in the detection of subclinical small and low-risk carcinomas with ultrasonography and fine needle aspiration cytology. However, central neck lymph node metastasis (CLNM) can occur in patients with PTMC. We evaluated the factors influencing CLNM in patients with PTMC. Methods: We reviewed medical records including clinical information and pathologic reports, and analyzed 622 patients with PTMC who underwent thyroid surgery from January 2002 to December 2012. Results: CLNM was detected in 119 patients (19.1%) of the 622 with PTMC. Lymph node metastasis occurred more frequently in males (P=0.025), and those with bilateral tumors (P=0.016), more than two tumors (P=0.035), tumor size greater than 5 mm (P＜0.001), and lymphovascular invasion (P=0.024). There were no statistically significant differences in age and capsular invasion. Multivariate analysis showed that significant factors affecting lymph node metastasis included age at operation (odds ratio [OR]=0.647, 95% confidence interval [CI]=0.422∼0.990, P=0.045), sex (OR=0.489, 95% CI=0.268∼0.891, P=0.020), tumor size (OR=3.034, 95% CI=1.761∼5.224, P＜0.001), and lymphovascular invasion (OR=15.036, 95% CI=1.450∼155.911, P=0.023). Conclusion: Age less than 45 years, male sex, tumor size greater than 5 mm, and lymphovascular invasion were risk factors associated with CLNM.