Predicting occult lymph node metastasis in level II using preoperative factors.

[BACKGROUND] Super-selective neck dissection which declining level II and V for better neck function preservation remains controversial in the treatment of papillary thyroid carcinoma (PTC). This study aims to explore association between occult lymph node metastasis (OLNM) in level II and preoperative clinical characteristics.

[METHODS] This retrospective study reviewed unilateral cN1b PTC patients who underwent surgery (2000-2017), with clinical lateral neck metastasis limiting in level III and IV. The OLNM in level II was assessed with preoperative clinical characteristics using logistic regression model; its association with pathological nodes distribution was examined with restricted cubic spline; the prognosis value of level II OLNM was evaluated using Kaplan-Meier method and Cox regression model.

[RESULTS] A total of 640 patients (mean [SD] age, 41[11.3] years; 440[68.8 %] female individuals; 307[48.0 %] with OLNM in level II) were analyzed. Primary tumor size (>1.5 cm, OR, 1.625[1.174-2.252]; P = 0.003) and clinical positive lymph nodes (multiple, OR, 4.241 [2.283-8.506]; P < 0.001) are associated with elevated risk of level II OLNM. A non-linear relationship was found between level II OLNM and metastatic lymph nodes number in levels III and IV. No significant difference in all-site recurrence-free survival (RFS) or regional RFS was found between patients with or without level II OLNM, even after adjusting other potential risk factors.

[CONCLUSION] The primary tumor size and metastatic burden in adjacent cervical compartments are associated with risk of level II OLNM, super-selective neck dissection could be considered in patients with small primary tumor cancer and low metastatic burden.