Ultrasonic characteristics

A total of 749 thyroid nodules in 627 patients were enrolled in this study. The ORs of nodules that were solid or almost completely solid, hypoechoic, very hypoechoic, taller than wide, lobulated or irregular, or that had extrathyroidal extension, peripheral calcifications, and punctate echogenic foci were rated as greater than 1. All others were rated at less than 1.

The ORs of malignant and benign nodules were calculated and are shown in Table 1.

Table 1 Comparison of ultrasonic signs between the malignant nodules and benign nodulesThe new assignment process

According to the OR value calculated from Table 1 it was found that thyroid nodules with ultrasonic signs, that were solid or almost completely solid, hypoechoic or very hypoechoic, taller than wide, lobulated, irregular or had extrathyroidal extension, and peripheral calcifications or punctate echogenic foci, were risk factors for malignant nodules (OR > 1). The authors assigned those ultrasonic signs 1 point, while the others were assigned 0 points.

Compared with the 2017 ACR guideline, ultrasonic signs that had been assigned 2 or 3 points were now assigned 1 point, while those ultrasonic signs that had been assigned 1 point, or 0 points, were now assigned 0 points (Fig. 2).

Fig. 2

Simplified assignment process, comparison with 2017 ACR-TI-RADS

Comparison of the malignancy rate of thyroid nodules

According to the malignancy rate recommended by the guidelines, the authors calculated the malignancy rate of the thyroid nodules in this study and compared it with the 2017 ACR-TI-RADS and 2020 C-TI-RADS. It was suggested that the actual malignancy rate in this calculation was not exactly the same as that of the guidelines (Table 2).

Table 2 Comparison of malignancy risk between the various guidelinesThe diagnostic efficacy of the new assignment process

According to the assignment results, the new thyroid nodule scores of each patient and the malignancy rate of each score were calculated (Table 3).

Table 3 Nodule’s score and malignant rate of the new assignment process

Then, an ROC curve was created (Fig. 3). The area under the ROC curve (AUC) was 0.867 (95% confidence interval, 0.836–0.898). Using 3 points as the best cutoff to diagnose benign and malignant thyroid nodules, the sensitivity and specificity were 94.03% and 67.39%, respectively.

Fig. 3

ROC of the new assignment process, 2020 C-TIRADS, and 2017 ACR-TIRADS to diagnose benign and malignant thyroid nodules

The simplified TI-RADS (sTI-RADS) was proposed and compared with the 2020 C-TI-RADS

According to the scoring results of the thyroid nodules, the authors referred to the 2020 C-TI-RADS grading system and classified 0 points as sTI-RADS 3, with a malignancy rate of < 2%. One point was classified as sTI-RADS 4a, with a malignancy rate of 2–10%; 2 points as sTI-RADS 4b, with a malignancy rate of 10–50%; 3 points as sTI-RADS 4c, with a malignancy rate of 50–90%; and 4 and 5 points as sTI-RADS 5, with a malignancy rate of > 90%.

In contrast to the 2020 C-TI-RADS, 4 and 5 points were classified into five categories of sTI-RADS, and the malignancy rate was > 90%, while 3 and 4 points were classified into 4C categories, and 5 points were classified into 5 categories of 2020 C-TI-RADS (Fig. 4).

Fig. 4

The assignment process of sTI-RADS, and comparison with 2020 C-TI-RADS

An “almost completely solid” composition designation was added to sTI-RADS and 1 point was assigned to the solid composition. For echogenicity, sTI-RADS included “hypoechoic” and assigned 1 point as very hypoechoic. For echogenic foci, sTI-RADS included peripheral calcifications and assigned 1 point for punctate echogenic foci. However, the ACR-TI-RADS assigned III was defined as 0 points, whereas the 2020 C-TI-RADS assigned III was defined as 1 point. In the sTI-RADS, the authors followed the 2017 ACR-TI-RADS scoring criteria and classified them into III, which was defined as 0 points (Fig. 4).

The diagnostic performance of sTI-RADS, 2017 ACR-TI-RADS, and 2020 C-TI-RADS

Among the sTI-RADS, 2017 ACR-TI-RADS, and 2020 C-TI-RADS, the sTI-RADS had the highest specificity, accuracy, and positive predictive value (67.39%, 85.85%, and 86.68%, respectively), followed by the 2020 C-TI-RADS (64.78%, 85.58%, and 85.86%, respectively) and 2017 ACR-TI-RADS (46.09%, 82.91%, and 80.59%, respectively). The sTI-RADS had the highest Youden index (Table 4). In addition, the sTI-RADS had the maximum AUC (0.867), followed by the 2020 C-TI-RADS (0.865) and 2017 ACR-TI-RADS (0.861) (Fig. 3).

Table 4 Comparison of diagnostic efficiency in two guidelines and sTI-RADSSupplement to sTI-RADS

According to the thyroid nodule sTI-RADS score, there was a lack of classification of sTI-RADS 1 and sTI-RADS 2. Therefore, the authors classified the absence of nodules in the thyroid gland as sTI-RADS 1 with a malignancy rate of 0% and glial cysts as sTI-RADS 2 with a malignancy rate of 0%. Compared with the 2020 C-TI-RADS, the assignment result of -1 point was no longer applicable (Fig. 5).

Fig. 5

There was absence of nodules in the thyroid gland classified into as sTI-RADS 1 and 2020 C-TI-RADS 1. And the glial cysts are classified into as sTI-RADS 2, while -1 point was classified into as 2020 C-TI-RADS 2

Consistency of test results

FNAB or surgery confirmed which of 123 thyroid nodules were malignant (n = 90) or benign (n = 33). The ICC values of the 2017 ACR-TI-RADS, 2020-C-TI-RADS, and sTI-RADS were all greater than 0.80. Therefore, the intragroup diagnostic consistency of the five ultrasound doctors was good (Table 5). When comparing the diagnostic consistency between ultrasound doctors at the same level or with the same title, the kappa value of sTI-RADS was the highest, indicating that the intergroup diagnostic consistency was good only for sTI-RADS. The sTI-RADS had the highest accuracy, PPV, and Youden index; the Youden index showed an upward trend with an increase in the seniority of ultrasound doctors. A comparison of the diagnostic efficacy of the three scoring systems among the five ultrasound doctors is shown in Table 5.

Table 5 Comparison of diagnostic efficacy of different grading systems among five doctors