A NOVEL SCORING SYSTEM FOR RISK OF PAPILLARY THYROID CANCER METASTASES IN LYMPH NODES POSTERIOR TO THE RIGHT OF THE RECURRENT LARYNGEAL NERVE

Background: Papillary thyroid carcinoma (PTC) can frequently metastasize to the cervical lymph node, especially in the central compartment. Some surgeons believe that dissection posterior to the right recurrent laryngeal nerve lymph node (PRRLN-LN) is unnecessary because of the low metastasis rate and high complication risk. However, persistent metastatic lymph nodes may have a higher recurrence rate, surgical risk, and complications. Thus, it is important to distinguish patients who require PRRLN-LN dissection. The aim of this study was to identify the risk factors for PRRLN-LN metastasis (LN-prRLN), and to establish a scoring system, to help determine whether PRRLN-LN dissection is required in PTC patients. Methods: The study comprised 821 patients with primary PTC in the right or both lobes who had undergone right lobectomy or total thyroidectomy with only right, or bilateral central compartment dissection with/without lateral neck dissection, between January 2010 and June 2016 in our institution. Participants were randomly allocated to development and validation cohorts in a 2:1 ratio. A nomogram-based predictive model for LN-prRLN was established based on the risk factors identified in the development cohort. Results: LN-prRLN was diagnosed pathologically in 15.1% (124/821) of patients from the entire cohort. Multivariate analysis identified age (odds ratio [OR] 0.964, 95% confidence interval [CI] 0.945–0.983; P<0.001), tumor size (OR 1.536, 95%CI 1.135–2.079; P=0.005), extrathyroidal extension (OR 2.271, 95%CI 1.368–3.770; P=0.002), clinically-involved right central compartment lymph node metastasis (OR 1.643, 95%CI 1.055–2.559; P=0.028), and right lateral lymph node metastasis (OR 4.271, 95%CI 2.325–7.844; P<0.001) as predictors of LN-prRLN. A risk model was established and well validated. Calibration curves to evaluate the nomogram in both the development and validation cohorts revealed a C-index of 0.756±0.058 and 0.745±0.042, respectively. Conclusions: Our scoring system may be useful for helping surgeons to decide which patients should undergo dissection of the PRRLN-LN. Abbreviations: ATA = American Thyroid Association; CCD = Central compartment dissection; CI = Confidence interval; C-index = The concordance index; ETE = Extrathyroidal extension; FNA = Fine-needle aspiration; LNM = Lymph node metastasis; LN-prRLN = Posterior to the right recurrent laryngeal nerve lymph node metastasis; OR = Odds ratio; PRRLN-LN = Posterior to the right recurrent laryngeal nerve lymph node; PTC = Papillary thyroid carcinoma; RLN = Recurrent laryngeal nerve.