The Prevalence of Extranodal Extension in Papillary Thyroid Cancer Based on the Size of the Metastatic Node: Adverse Histologic Features Are Not Limited to Larger Lymph Nodes

Extranodal extension (ENE) is a prognostic indicator of aggressiveness for papillary thyroid cancer (PTC). The association between the size of metastatic nodes and the prevalence of ENE has not been previously explored. However, there is a common belief that small lymph nodes with metastatic disease do not significantly impact patient outcome. This study investigates the relationship between the prevalence of ENE and the size of a positive lymph node. Linear dimensions and malignant histological characteristics of 979 metastatic lymph nodes from 152 thyroid cancer patients were retrospectively analyzed. Data was analyzed using chi-square tests and multilevel logistic regression modeling. ENE was present in 144 of 979 lymph nodes; the sizes of the involved lymph nodes ranged from 0.9 to 44 mm. ENE was identified in 7.8% of lymph nodes measuring ≤ 5 mm, 18.9% between 6 and 10 mm, 23.1% between 11 and 15 mm, 25.0% between 16 and 20 mm, and 14.0% between 21 and 25 mm in size. The association between node size and ENE status was significant (odds ratio (OR) = 1.07, confidence interval (CI) = [1.04, 1.11]). The size of the metastatic focus directly correlated with ENE (OR = 1.07, 95% CI = [1.07, 1.14], p value < 0.001). Increasing lymph node size increases the likelihood of ENE for metastatic PTC. Importantly, small positive lymph nodes can also harbor ENE to a significant extent. Further studies are required to determine the clinical and prognostic significance of lymph node size and the presence of ENE.