To analyze the influencing factors of maximum Young's modulus (Emax) of shear wave elastography (SWE) of thyroid nodules, and to explore whether grouping by the most significant influencing factors can improve the diagnostic value of Emax.

A total of 368 patients (with 413 nodules in total) who underwent surgery for thyroid nodules at Bethune Hospital Affiliated to Shanxi Medical University from January 2017 to November 2019 were retrospectively selected. All patients underwent preoperative two-dimensional ultrasound and SWE examination. The size, number, shape, position, internal composition, echo, margin, and calcification of nodules were recorded by conventional ultrasound. Emax values and the depths of nodules were recorded by SWE. Spearman rank correlation was used to screen the influencing factors of Emax value of thyroid malignant nodules. Multiple linear regression analysis was performed on the related factors, and the diagnostic value of Emax value was further analyzed according to the grouping of the most significant influencing factors.

Among 413 thyroid nodules, 106 were benign and 307 were malignant. The results of correlation analysis showed that the size, margin, and calcification of thyroid malignant nodules were positively correlated with Emax value (r=0.477, 0.244, and 0.256, respectively; P＜0.05 for all), while the depth of thyroid nodules was negatively correlated with Emax value (r=-0.132, P＜0.05). Multiple linear regression analysis showed that nodule size had the most significant effect on Emax value (standardized partial regression coefficient, 0.537). The nodules were divided into group A (maximum diameter ≤1 cm), group B (1 cm < maximum diameter ≤2 cm), and group C (2 cm < maximum diameter ≤3 cm) according to their maximum diameter. The cutoff value was 36.0 kPa, the area under the ROC curve (AUC) was 0.830, and the sensitivity and specificity were 73.0% and 81.1%, respectively, for the diagnosis of thyroid malignant nodules not grouped by Emax value. The cutoff value of Emax for diagnosis of thyroid malignant nodules in groups A, B, and C according to the size of nodules was 33.7 kPa, 37.8 kPa, and 57.1 kPa, and AUC was 0.832, 0.889, and 0.952, respectively. The diagnostic sensitivity and specificity in group A were 68.0% and 87.9% in group A, 89.0% and 82.1% in group B, and 94.7% and 90.9% in group C, respectively. Compared with the nodules not grouped by nodule size, the AUCs of groups A, B, and C increased to varying degrees, the diagnostic sensitivity and specificity of Emax value decreased in group A, and increased in groups B and C.

The Emax value of thyroid nodule is most significantly affected by the size of thyroid nodules. Grouping by the size of thyroid nodule can improve the diagnostic value of Emax value for thyroid nodules with the maximum diameter >1 cm. When using Emax value to diagnose the nature of thyroid nodules, it is recommended to use different cutoff values for different nodule sizes.