Patterns of lymph node metastasis in Level IIB and Contralateral Level VI for Papillary Thyroid Carcinoma with pN1b and Safety of low collar extended incision for neck dissection in Level II
Authors: Ning Yudong , Zeng Dingfen , Zhou Yuqiu , Ma Linjie , Dong Shuang , Cai Yongcong , Li Chao 
Published: December 2022

Objective
To explore relevant clinical factors of Level IIB and contralateral Level VI lymph node metastasis and evaluate the safety of low -collar extended incision(LCEI) for lymph node dissection in level II for papillary thyroid carcinoma(PTC) with pN1b.
Method
A retrospective analysis was performed on 218 patients with PTC with pN1b who were treated by surgery in the Head and Neck Surgery Center of Sichuan Cancer Hospital from September 2021 to May 2022.The data on age, gender, body mass index(BMI), tumor location, maximum tumor diameter, multifocality, Braf gene, T staging, surgical incision style and lymph node metastasis in each cervical subregion were collected. The chi-square test were used for comparative analysis of relevant factors. All statistical analysis was completed by SPSS.24 software.
Result
Each subgroup on gender, age, BMI, multifocality ,tumor location, extrathyroidal extension, Braf gene, lymphatic metastasis in level III, level IV and level V had no statistical difference in the positive rate of lymph node metastasis in level IIB(P > 0.05).In contrast, patients with bilateral lateral cervical lymphatic metastasis were more likely to have lymphatic metastasis in level IIB than those with unilateral lateral cervical lymphatic metastasis, with a statistically significant difference (P = 0.000). Besides, lymph node metastasis in level IIA was significantly associated with lymph node metastasis in level IIB (P = 0.001). The LCEI group had the similar lymphatic metastasis number and lymphatic metastasis rate in both level IIA and level IIB with the L-shaped incision group(P > 0.05).Patients with ipsilateral central lymphatic metastasis had 86 cases(78.2%). While patients with contralateral central lymphatic metastasis accounted for 56.4%.The contralateral central lymphatic metastasis rate was not correlated with age, BMI, multifocality, tumor invasion and ipsilateral central lymphatic metastasis, and there was no statistical difference (P > 0.05). The contralateral central lymphatic metastasis in males was slightly higher than that in females, and the difference was statistically significant (68.2%vs48.5%, P = 0.041).
Conclusion
Lymphatic metastasis in Level IIA was an independent predictor of lymphatic metastasis in Level IIB. When bilateral lateral cervical lymphatic metastasis or lymph node metastasis of level IIA are found, lymph node dissection in level IIB is strongly recommended.When unilateral lateral cervical lymphatic metastasis and lymphatic metastasis in level IIA is negative, lymph node dissection in level IIB may be performed as appropriate on the premise of no damage to the accessory nerve.LCEI is safe and effective for lymph node dissection in Level II. When the tumor is located in unilateral lobe, attention should be paid to the contralateral central lymph node dissection because of the high lymphatic metastasis rate.