Risk Factors Of Lymph Node Posterior To The Right Recurrent Laryngeal Nerve Metastasis In Papillary Thyroid Carcinoma

BackgroundThyroid cancer is one of the most common malignant tumors of the endocrine system and the head and neck,and is the fourth common cancer in China now.The most common pathological subtype of thyroid cancer is papillary thyroid carcinoma(PTC).PTC has clinical features of low malignancy,well differentiation,and slow progression of disease.But it is prone to cervical lymph node metastasis,especially the central compartment(Level Ⅵ).There are massive lymphatic and adipose tissue posterior to the right recurrent laryngeal nerve.The right recurrent laryngeal nerve ascends through the adipose tissue of the right central compartment,which are divided into two subgroups: lymph node anterior to the right recurrent laryngeal nerve(VIa compartment)and lymph node posterior to the right recurrent laryngeal nerve(VIb compartment or LN-pr RLN).Because LN-pr RLN is deep and difficult to dissect,it remains controversial whether to dissect LN-pr RLN.To the end,we performed this retrospective study which enrolled 469 patients with PTC to identify the clinicopathological risk factors for LN-pr RLN metastasis,investigate the cut-off point of these risk factors and indication for LN-pr RLN dissection in PTC.MethodPatients with PTC including papillary thyroid microcarcinoma(PTMC)who were pathologically diagnosed and underwent LN-pr RLN dissection in the Department of General Surgery of Zhongshan Hospital Affiliated to Xiamen University from January2016 to September 2020 were included.Their clinicopathological information was reviewed,including gender,age,preoperative ultrasonography and computed tomography(CT)imaging data,thyroid function tests,operation records,pathological reports and surgical complications.According to the inclusion criteria and exclusion criteria,a total of 469 cases were included in the group.These patients were analyzed retrospectively.Univariate and multivariate Logistic regression were used to analyze the risk factors of LN-pr RLN metastasis,and then receiver-operator characteristic(ROC)curve and Youden’s index were used to calculate the cut-off point.ResultsThe rate of central lymph node metastasis(CLNM)was 52.5%(246/469),the rate of VIa central lymph node metastasis was 48.2%(226/469),and the rate of LN-pr RLN metastasis was 16.6%(246/469).Univariate analysis showed that VIa central lymph node metastasis,right lateral lymph node metastasis,tumor size in right thyroid,tumor multifocality,capsular invasion and extrathyroidal extension,lymphovascular invasion were significant risk factors for LN-pr RLN metastasis.LN-pr RLN metastasis was not associated with age,gender,tumor bilaterality and nerve invasion.On multivariate Logistic regression,VIa central lymph node metastasis,right lateral lymph node metastasis,tumor size in right thyroid,tumor multifocality,lymphovascular invasion were independent risk factors for LN-pr RLN metastasis.The ROC analysis showed that the areas under the ROC curves for the prediction of LN-pr RLN metastasis by the risk factors tumor size in right thyroid > 1.25 cm,number of VIa central lymph node metastasis > 2.5,number of right lateral lymph node metastasis > 1.5 were0.646,0.711 and 0.625(P<0.05),respectively.Among 469 patients,5 patients had postoperative hemorrhage,3 patients had lymphatic leakage,60 patients underwent parathyroid glands autotransplantation,4 patients had temporary hoarseness and 5patients transient slight numbness of hands and feet.ConclusionThe removal of LN-pr RLN should be considered when dissecting the right central lymph node in patients with papillary thyroid carcinoma,especially for the patients with tumor size in right thyroid > 1.25 cm,number of VIa central lymph node metastasis ≥3,number of right lateral lymph node metastasis ≥2.LN-pr RLN dissection is safe and feasible with the support of experience and technology,and the type and incidence rate of complications are acceptable.