Prediction and investigation of the potential risk factors for the upper mediastinal metastasis of papillary thyroid carcinoma

Abstract

Objective: To predict and investigate the potential risk factors for the upper mediastinal metastasis of papillary thyroid carcinoma (PTC). Methods: This study was a prospective cohort study. The admission criteria were patients with untreated thyroid cancer diagnosed in Cancer Hospital, Chinese Academy of Medical Sciences from December 2013 to December 2015, and positive lymph node (cN1, including cN1a and cN1b) was diagnosed by ultrasound. All patients underwent neck to thorax enhanced Computed Tomography (CT) examination preoperatively. All patients with suspected upper mediastinal lymph node metastasis experienced suspicious regional dissection, and those who had not undergone surgery and whose postoperative pathology was non-papillary thyroid carcinoma were excluded. Kaplan-Meier method was selected for survival analysis and all the factors were analyzed by multivariate Logistic regression. Results: Of the 248 patients, 54 were prompted by postoperative pathology for upper mediastinal lymph node metastasis, 86 cases were phase T1, 94 cases were phase T2, 17 cases were phase T3 and 51 cases were phase T4, 21 cases were N1a phase and 227cases were N1b phase. There was a statistically significant difference in the T-phase and N-phase between the upper mediastinal lymph node metastasis group and no upper mediastinal lymph node metastasis group(P<0.05). Univariate analysis showed that among the preoperative relevant factors, ultrasound tumor length> 2 cm, ultrasound tumor bilaterally, CT double neck lymph node metastasis, increased thyroglobulin (Tg), and increased anti-thyroglobulin antibody (ATG) were all risk factors for upper mediastinal lymph node metastasis(all P<0.05). Among the postoperative factors, bilateral tumor, double neck lymph node metastasis, tumor invasion of the recurrent laryngeal nerve, trachea, esophagus or larynx, T3 staging, T4 staging, total number of metastatic lymph nodes>10, the number of metastatic lymph nodes in level Ⅵ>3 and >6, the proportion of metastatic lymph nodes in level Ⅵ>1/2, the number of metastatic lymph nodes in level Ⅳ> 5 and metastatic proportion >1/3 are risk factors for metastasis of upper mediastinal lymph node(all P<0.05). Multivariate analysis showed that CT indicated double neck lymph node metastasis, increased Tg, increased ATG, the proportion of metastatic lymph nodes in level Ⅵ >1/2, and in level Ⅳ>1/3 are independent risk factors for upper mediastinum lymph node metastasis(all P<0.05). The 5-year recurrence-free survival rates of the upper mediastinal lymph node metastasis group and the no upper mediastinal lymph node metastasis group were 92.3% and 94.8% respectively, and the difference was not statistically significant(P=0.307). Conclusions: For preoperative ultrasound considering the presence of lymph node metastases, enhanced neck to thorax CT should be performed routinely. When bilateral cervical lymph node metastasis is determined by CT, or endocrine tests suggest abnormally increased antibodies, attention should be paid to the upper mediastinal lymph nodes metastasis. In the course of neck dissection, if more lymph node metastases in level Ⅵ and level Ⅳ were detected, surgeons should be vigilant of the upper mediastinal metastasis. The prognosis of patients underwent complete mediastinal dissection is not significantly different from that of patients without mediastinal metastasis.