Risk factors of occult lymph node metastasis of levels Ⅲ and Ⅳ in papillary thyroid carcinoma

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Objective: To investigate the potential risk factors for occult lateral cervical lymph node metastasis (LNM) to levels Ⅲ and Ⅳ in patients with papillary thyroid carcinoma (PTC) and the necessity of super-selective lateral lymph node dissection for patients harboring these metastases. Methods: This prospective study included PTC patients who were operated by the same surgeon in the Department of Head and Neck Surgery of Cancer Hospital, Chinese Academy of Medical Sciences from October 2015 through October 2019. Preoperative ultrasound and enhanced Computer Tomography (CT) did not denote suspected enlarged lymph nodes in the lateral neck. All patients underwent lymph node dissection in levels Ⅲ and Ⅳ on the basis of original thyroid collar incision after LNM to level Ⅵ was confirmed by preoperative fine needlebiopsy or intraoperative frozen pathology. Results: Of all 143 patients, 74 (51.7%) had occult LNM in levels Ⅲ and Ⅳ confirmed by postoperative pathology. The average number of metastasized lymph nodes in levels Ⅲ and Ⅳ was 2.64±1.80, and that in level Ⅵ was 3.77±3.27. There was a significant linear positive correlation between the number of metastasized lymph nodes in level Ⅵ and that in levels Ⅲ and Ⅳ (r=0.341, P<0.001). That the metastasized lymph nodes in level Ⅵ equals three was the best predictor of occult lateral LNM to levels Ⅲ and Ⅳ. Univariate analysis showed that age <55 years, tumor size ≥2.0 cm, number of metastasized lymph nodes in level Ⅵ ≥3, and percentage of metastasized lymph nodes in the total number of dissected lymph nodes in level Ⅵ >50% were associated with occult LNM in levels Ⅲ and Ⅳ (P<0.05). Multivariate analysis showed that number of metastasized lymph nodes in level Ⅵ≥3 was an independent risk factor for occult LNM in levels Ⅲ and Ⅳ (P=0.006). Conclusions: Age, tumor size and LNM in level Ⅵ were associated with occult lateral LNM in PTC patients. Lymph node dissection in levels Ⅲ and Ⅳ could be considered for selective patients, since it will help to avoid secondary operation for residual tumor or recurrence resulted from insufficient treatment without increasing the incidence of complications or affecting patients' appearances.