Surgical treatment and prognosis values of extranodal extension to recurrent laryngeal nerve in papillary thyroid carcinoma

Purpose Recurrent laryngeal nerve (RLN) invasion by extranodal extension (ENE) is a rare condition that may occur in papillary thyroid cancer (PTC), and it has never been characterised in the literature.Our research aims to investigate the clinical significance of ENE to RLN including its effect on vocal cord function, relationship with the aggressive behaviour of PTC, and optimal surgical methods. Methods A total of 3119 patients, including 2868 patients without RLN invasion, 251 patients with RLN invasion [categorised into the ENE invasion group ( n = 55) and extrathyroidal extension (ETE) invasion group ( n = 196)] were analyzed retrospectively. Data on clinicopathological characteristics, vocal cord paralysis (VCP), postoperative complications, surgical methods, rates of recurrence and metastasis were collected. Predictive disease-free survival (DFS) was analysed using the Kaplan–Meier method. Results The ENE invasion group showed a similar rate of VCP and DFS compared with the ETE invasion group ( P = 0.15, P = 0.38, respectively). Sharp separation applied on the invaded nerves preserves the visual integrity of the RLN without significantly reducing the DFS ( P > 0.05). ETE or ENE to RLN, lymph nodes metastasis (LNM), and T4 stage were independent factors for total recurrence [ P = 0.04, hazard ratio (HR), 1.97 (1.04–3.75); P = 0.00, HR, 4.63 (2.24–9.54); P = 0.00, HR, 3.63 (1.94–6.77); P = 0.00, HR, 6.1 (3.24–11.50)]. RLN invasion, both by ETE or ENE, was significantly associated with reduced DFS ( P = 0.00; P = 0.00, respectively). Conclusions ENE to RLN, while rare, has not previously been well-studied. Our interesting premise and important findings including ENE to RLN has the same poor prognostic impact on recurrence as does invasion of the RLN by ETE and surgical management for the invaded RLN that preserves its visual integrity without compromising DFS. Those novel findings indicate that ENE to RLN could be considered as an additional factor beyond post-operative disease status and risk stratification, and it would be a valuable addition to further individualise treatment/surveillance for PTC.