Comprehensive analysis of carotid triangle lymph node metastasis in papillary thyroid carcinoma.

BACKGROUND: Carotid triangle lymph nodes (CAT LN) represent a frequently overlooked region during lateral neck dissection (LND) in patients with papillary thyroid carcinoma (PTC), and their metastatic characteristics remain poorly defined. This study aimed to comprehensively evaluate the clinicopathological risk factors and metastatic patterns associated with CAT LN involvement. METHODS: This single-center retrospective study analyzed 410 lateral neck dissections performed in 380 patients with PTC. The lateral neck side, paired with the ipsilateral thyroid lobe and ipsilateral central compartment, was used as the unit of analysis. Clinicopathological variables associated with CAT LN metastasis were evaluated using univariate and multivariate logistic regression analyses. The status of lymph node metastasis in other cervical regions was compared between CAT-positive and CAT-negative neck sides. Conditional probability analysis was further performed to explore predominant metastatic pathways according to tumor location. RESULTS: CAT LN metastasis was observed in 174 of 410 dissected neck sides (42.4%). Multivariate analysis identified tumor size >2 cm (OR = 2.243, 95% CI: 1.431-3.547, P < 0.001), tumor location, and aspect ratio ≥1 (OR = 2.181, 95% CI: 1.280-3.802, P = 0.005) as independent predictors of CAT LN metastasis. Upper-pole tumors had a significantly higher risk (OR = 1.791, 95% CI: 1.145-2.816, P = 0.011), while lower-pole tumors had a lower risk (OR = 0.295, 95% CI: 0.147-0.559, P < 0.001) compared to middle-pole tumors. CAT-positive necks demonstrated significantly higher metastatic rates in levels II, III, and VI and had a greater total number of involved nodal levels (all P < 0.05), indicating a substantially higher metastatic burden across cervical lymph node regions. Conditional probability analysis revealed multiple potential metastatic putative pathways leading to the carotid triangle (CAT). Moreover, the lymphatic metastatic putative routes to the CAT were strongly correlated with primary tumor location: CAT LN metastasis in upper-pole tumors appeared to preferentially spread through the lateral cervical lymphatic pathway, whereas CAT involvement in middle-pole tumors was more likely to arise through upward dissemination from the central compartment. CONCLUSIONS: CAT LN metastasis is common among PTC patients undergoing LND and is associated with tumor size, tumor location, aspect ratio, and overall regional nodal burden. The metastatic pattern of CAT LN appears to vary according to tumor location, suggesting distinct lymphatic dissemination pathways. Increased awareness of this anatomical region may improve surgical completeness and optimize lateral neck dissection strategies in selected high-risk patients.