Predicting recurrent laryngeal nerve invasion by preoperative ultrasonography in patients with thyroid carcinoma

BACKGROUND: For thyroid cancer staging, evaluation of extent of local invasion, including recurrent laryngeal nerve (RLN), may assist surgical decision-making. METHODS: This prospective study evaluated patients who underwent thyroidectomy at a single tertiary-level academic institution. Patients with complete clinical information and ultrasound imaging of thyroid carcinoma and RLN were enrolled. Those who had thyroidectomy before or did not fit the above conditions were excluded. Patients were assigned to either a development or validation cohort. Development of models was constructed in a primary cohort based on preoperative ultrasound features and clinicodemographic data from August 2020 to December 2021. Validation of the models was then performed on an independent cohort between January and March of 2022. Multivariate logistic regression and nomograms were mainly used for statistical analysis. RESULTS: Using data from 816 patients (80 RLN invasion), we built nomogram 1 based on age [95% confidence interval (CI): 1.315 to 145.933, P=0.029], body mass index (BMI; 95% CI: 1.228 to 10.874, P=0.020), tumor size (95% CI: 4.677 to 1,373.1, P=0.002), tumor adjacent to medial (95% CI: 1.816 to 26.713, P=0.005) and posterior thyroid capsules (95% CI: 5.567 to 756.583, P=0.001), and distance <1 mm between tumor and the RLN (95% CI: 10.389 to 826.746, P<0.001). Nomogram 2 was built based on tumor adjacent to the posterior thyroid capsule (95% CI: 2.922 to 53,074.51, P=0.017), distance <1 mm between tumor and the RLN (95% CI: 1.478 to 1,241.646, P=0.029), and loss of typical fascicular echotexture of the RLN along the long axis (95% CI: 35.11 to 53,272.81, P<0.001). In the validation cohort, nomogram 1 and 2 showed sensitivities of 94.74% and 57.89%, specificities of 74.12% and 95.29%, positive predictive values (PPV) of 45.00% and 73.26%, negative predictive values (NPV) of 98.43% and 91.03%, accuracies of 76.92% and 88.46%, and C-indices of 0.86 and 0.89. CONCLUSIONS: Preoperative ultrasound is a feasible approach to evaluate RLN invasion in patients with thyroid carcinoma. Nomogram 1 may sensitively identify the risk of RLN invasion, and it may be checked using the more specific and accurate nomogram 2 to reduce false positives.