Analysis of 665 thyroid nodules using both EU-TIRADS and ACR TI-RADS classification systems

Abstract

Background: Ultrasound-based classification systems allow stratification of thyroid nodules to recommend fine-needle aspiration (FNA) based on their malignancy risk. However, these have discrepancies that may have an impact in thyroid cancer detection. We aimed to compare European Thyroid Association (EU-TIRADS) and American College of Radiology (ACR TI-RADS), in terms of FNA indication and diagnostic performance.

Methods: Retrospective study of 665 thyroid nodules from 598 patients who underwent ultrasound and fine-needle aspiration at a tertiary-care institution between January 1^st of 2016 and July 31^st of 2019. Based on their sonographic features they were classified according to the EU-TIRADS and ACR TI-RADS classification and then their cytological results were obtained. Differences in FNA indications according to these two classifications were analysed. In patients who underwent surgical removal of the nodules, the final pathological diagnosis was obtained.

Results: A statistically significant association was found between EU-TIRADS and ACR TI-RADS classification systems (p < 0.001). ACR TI-RADS allowed greatest reduction in FNA performed (32% vs 24.5%). A different risk category was obtained in 174 (26.1%) nodules, mostly higher with EU-TIRADS. The indication to FNA changed in 54 (8.1%) nodules (49 only indicated following EU-TIRADS recommendations), of which 4 had Bethesda IV and 5 had Bethesda III cytology. The FNA indication in a higher number of nodules using EU-TIRADS was due to difference in the dimensional threshold for FNA on low-risk nodules; to the fact that hypoechogenicity in a mixed nodule ascribes it moderate risk, while using ACR TI-RADS it would only be considered of low risk, and to the use of isolated sonographic features, namely marked hypoechogenicity, microcalcifications and irregular margins, to automatically categorize a nodules as high risk in EU-TIRADS, while ACR TI-RADS requires a group of potentially suspicious features to consider a nodule of high risk. The analysis of pathology proven nodules revealed equally good sensitivity of both systems in the detection of malignancy, but weak specificity, slightly greater with ACR TI-RADS (27.1% vs 18.6%).

Conclusions: The EU-TIRADS and ACR TI-RADS are both suitable to assess thyroid nodules and through risk stratification avoid unnecessary FNA. FNA was less performed using ACR TI-RADS, which was slightly more efficiency in excluding malignancy.

Keywords: ACR TI-RADS; EU-TIRADS; Fine-Needle Aspiration; Thyroid Neoplasms; Thyroid Nodules; Ultrasonography.

Fig. 1

Differences between ACR TI-RADS and EU-TIRADS classification systems. In ACR TI-RADS, the risk category is based on a sum of points assigned to 5 sonographic features. In EU-TIRADS a specific feature instantly classifies the nodule into one category. Adapted from references 3 and 6. Adapted from references 3 and 6

Fig. 2

Diagnostic Categories of the Bethesda System for Reporting Thyroid Cytopathology

Fig. 3

Final study sample selection after applying exclusion criteria (size < 10 mm, non-diagnostic cytology). AUS/FLUS = atypia of undetermined significance/follicular lesion of undetermined significance

Fig. 4

Risk Categories of the thyroid nodules assigned according to ACR TI-RADS (purple) and EU-TIRADS (blue)

Fig. 5

Representative images of nodules with different risk categories according to ACR TI-RADS and EU-TIRADS. A – nodule with mixed composition with isoechoic solid component (category ACR 2/EU 3); B – solid nodule markedly hypoechoic (category ACR 4/ EU 5); C – solid isoechoic nodule with punctate echogenic foci (arrow, category ACR 4/EU 5); D – solid hypoechoic nodule with taller-than-wide morphology (category ACR 4/ EU 5); E – solid hypoechoic nodule with posterior bulging of thyroid’s contour, indicative of extrathyroidal extension (category ACR 5/EU 4)