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ECR 2019 / C-2490
ACR-TIRADS and Eu-TIRADS, are they so different?
Congress: ECR 2019
Poster No.: C-2490
Type: Educational Exhibit
Keywords: Head and neck, Thyroid / Parathyroids, Ultrasound, Ultrasound-Colour Doppler, Structured reporting, Decision analysis, Diagnostic procedure, Endocrine disorders, Neoplasia, Pathology
Authors: F. Diaz, I. García Duitama, A. Radosevic, A. Solano, C. V. Martinez Stocker, M. Vilas Gonzalez, A. Agustí; Barcelona/ES

Findings and procedure details



Is a scoring system, based in the US features of a given nodule. The higher the score, the greater the risk of malignancy, which would imply performing complementary interventions (namely FNA) for a better characterization of the lesion. Detailed description of the nodules features' and scores can be found in Figure 1. 



Fig. 1: Figure 1. The 2017 ACR-TIRADS system.
References: Tessler FN, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. Journal of the American College of Radiology. 2017 May;14(5):587–95.


It stratifies nodules into the following suspicion groups: Fig. 1

  • TR1: Benign: Cancer risk 0.3%. In this case, FNA is not indicated.

  • TR2: Not suspicious: Cancer risk 1.5%. Similarly to TR1, FNA not indicated.

  • TR3: Mildly suspicious: Cancer risk 4,8%.  FNA is indicated if nodule is more or equal than 2.5cm, and follow up if more or equal than 1.5cm.

  • TR4: Moderately suspicious: Cancer risk is 9.1%. FNA is indicated if nodule is more or equal than 1.5cm, and follow up if more or equal than 1 cm.

  • TR5: Highly suspicious: Cancer risk is 35%. FNA is indicated if nodule is more or equal than 1 cm, and follow up if more or equal than 0.5cm. 



Its main goal was to develop simplified classification system, and by this means, to reduce the interobserver variability and improve the reproductibility. It is based on "classic pattern categories".


Fig. 2: EU-TIRADS algorithm for classification of nodules and FNA decision-making.
References: Russ G, et al. European Thyroid Association Guidelines for Ultrasound Malignancy Risk Stratification of Thyroid Nodules in Adults: The EU-TIRADS. European Thyroid Journal. 2017;6(5):225–37.


It defines the following US categories:

  • Normal gland, no nodules (EU-TIRADS 1).

  • Benign (EU-TIRADS 2): Risk of malignancy close to 0%. FNA is not indicated, unless compressive symptoms.

  • Low risk (EU-TIRADS 3): Risk of malignancy 2-4%. Proceed to FNA if more than 20mm.
  • Intermediate risk (EU-TIRADS 4): Risk of malignancy 6-17%. Proceed to FNA if more than 15mm.

  • High Risk (EU-TIRADS 5): Risk of malignancy 26-87%. Proceed to FNA if more than 10mm. 

Table 1: EU-TIRADS SYSTEM. Categories are defined by the classic picture of nodules.
References: Russ G, et al. European Thyroid Association Guidelines for Ultrasound Malignancy Risk Stratification of Thyroid Nodules in Adults: The EU-TIRADS. European Thyroid Journal. 2017;6(5):225–37.


ACR-TIRADS and EU-TIRADS: practical points and differences 


Both the EU-TIRADS and ACR-TIRADS are practical, useful and very good classifications systems recently developed. They share common characteristics, but also several differences. Categorization differences are shown in Table 2, and the differences in terms of management are described in  Table 3 .


Table 2: ACR/EU - TIRADS differences in terms of classification of nodules.
References: Hospital del Mar, Hospital del Mar - Barcelona/ES


Table 3: ACR/EU - TIRADS differences in terms of management of nodules by risk category.
References: Hospital del Mar, Hospital del Mar - Barcelona/ES


  • EU-TIRADS It is a system that assigns each lesion into a risk group according to the presence of certain US findings.
  • ACR-TIRADS is a score-based system, according to the US features of a given nodule.


  • In ACR-TIRADS, the score increases in a summatory way with every US feature added. So, a nodule must have a sum of features to be classified into a determined risk category, instead of a definitory feature alone, as used by EU-TIRADS (5 definitory high risk characteristics).  


  • In EU-TIRADS, the threshold to perform FNA are 2cm (low risk - EU-TIRADS 3), 1.5cm (intermediate risk - EU-TIRADS 4) and 1cm (high risk - EU-TIRADS 5). 


  • In ACR-TIRADS, the threshold size to perform a FNA are 2.5cm (TR3), 1.5cm (TR4) and 1 cm (TR5).


  • In EU-TIRADS 5, the guideline recommends repeating the FNA in 3 months if the FNA result is benign, to exclude a false negative.  Fig. 7 Fig. 9


  • In EU-TIRADS, the threshold to indicate active surveillance is <1cm high-risk nodules (EU-TIRADS 5). No specific recommendation is made for low and intermediate risk nodules. Fig. 8 


  • In ACR-TIRADS, the threshold size to initiate active surveillance are 1.5cm (TR3), 1cm (TR4) and 0.5cm (TR5). The system states that performing a biopsy of a nodule between 5 and 9mm can be appropriated under certain circumstances (shared referring doctor - patient decision making).


  • The EU-TIRADS includes a standardized reporting form, which is more extensive, and may be more time consuming.


  • Only the EU TIRADS includes a visual diagram of the thyroid gland, to standardize nodule location for reporting.  Fig. 3


  • The EU-TIRADS normal gland (1 category)  doesn't exists in ACR-TIRADS, in which such category 1 represents a benign nodule. 


  • EU-TIRADS 2 means a benign nodule, and ACR-TIRADS 2 means a non-suspect nodule. Both of them have distinct US characteristics. EU-TIRADS 2 is the equivalent to ACR-TIRADS 1.  Fig. 4


  • Although there are differences among systems in categories 1 and 2, they don't imply changes in terms of patient's management.


  • ACR-TIRADS 2 is an intermediate category, which is not included in the EU-TIRADS.  Fig. 10  Fig. 12  Fig. 13


  • The EUTIRADS states that there are 4 US characteristics (non oval shape, irregular margins, microcalcifications or marked hypoechogenicity) that if present, would be enough to classify a nodule as a high risk one. Such findings where first described in 2002, having a high degree of specificity (83-84%), but low sensitivity (26-59%).  Fig. 11


  • The EU-TIRADS takes into account several factors and situations excluded from the given scheme, which may reduce its usability. Examples to this: macrocalcifications (ACR included with 1 point), and extrathyroidal extension (ACR included with 3 points). 


  • The EU-TIRADS considers the possibility of a nodule formed by coalition of smaller ones. 


  • Nodule growth seems to weigh less in EU-TIRADS than in ACR TIRADS. In ACR-TIRADS, they tell us specific parameters to consider significant growth: at least 20% in 2 diameters, at least 2mm or 50% or more increase in volume.


  • EU-TIRADS takes into account scars as very hypoechoic lesions, and downscale its category. Such scars could be mistaken as a highly suspicious nodule using ACR-TIRADS.  


  • Both systems recommend to check lymphadenopathies, specially in the intermediate and high risk, and puncture them in case of suspiction. Suspiction features are: globular shape, loss of normal echogenic hilium, peripheral (intead of hilar) flow, heterogeneity and gland-like tisue within the node.  Fig. 5   Fig. 6


  • Respecting the multinodular disease, the recommedation is to report at least the 3 nodules with highest TIRADS (EU-TIRADS) and a maximun of 4 (ACR-TIRADS). 


EU-TIRADS and ACR-TIRADS: The accumulated evidence


Both of them are newly developed or revisited systems designed to discriminate the high risk lesions, reducing in this way, the unnecessary complementary explorations such as FNA and surgery.


The ACR TIRADS has been used for a while, being a useful tool, with high degree of sensibility and specificity, to discriminate the lesions.

The EU-TIRADS is even newer, and due to this, more studies are needed to demonstrate its capacity to discriminate. We need more comparative studies with the most known classification systems used nowadays.


A recent published article compared in a prospective way 5 of the most used classification systems (ACR, ATA, AACE/ACE/AME, EU-TIRADS and K-TIRADS). It was shown that all of them have a very good discriminatory capacity, reducing the number of unnecessary biopsies, being particularly higher in the case of ACR. The article concluded that ACR showed a better overall performance, classifying half of the biopsies as unnecessary, with a false negative rate of 2% [4].


Other recent study published in 2018 studied the interobserver variability of the classification systems AAC/ACE/AME, ACR, ATA, EU-TIRADS, K-TIRADS and the interobserver concordance in the indication of FNA biopsy. When selecting the nodules to be performed the FNA biopsy, which is the main objective of this classifications, the interobserver agreement is substantial to almost perfect [5].


Another recent sudy from 2018 comparing and estimating the performance of ATA, AACE/ACE/AME, ACR-TIRADS in discriminating high risk citology nodules. 1077 thyroides nodules submitted to FNA were classified according the classification systems. OR y ROC curves for the high risk categories were calculated. The ACR-TIRADS had the highest área below the curve ROC for identifying high risk citology nodules. [6]


Other recent study in 2018 was conducted to evaluate the temporal stability of initial risk calculated with 5 systems, and determine whether the risk class increases during the follow up is indicative of malignancy. It was demonstrated that benign nodules tend to stay stable in time, and changes that require biopsies are rare. Development of new nodules are frequent, but few of them (less than 5%) are classified as a high risk. So, this means that benign nodules could be followed in a secure way with less intense surveillance protocols.[7]


A prospective study comprehending almost 1000 nodules submitted to FNA, in which the US images were analyzed and classified by 4 experts, according the systems BTA, ATA y ACE/AME/AACE. It was revealed that those classification systems had high PPV for malignancy in high risk cases. [8]


Another study studied the validity of 6 US characteristics (mild hypoechogenicity, marked hypoechogenicity, irregular/microlobulated margins, microcalcifications, taller than wide shape and thin halo abscence) to stratify the thyroid nodules in iodine deficiency áreas in Austria. It was demonstrated that all criteria but mild hypoechogenicity were significantly more frequent in thyroid cancer than in benign nodules.This supports the use of EU-TIRADS. Apart from the mild hypoechogenicity, the US criteria can be applied to stratify the thyroid nodules risk in iodine deficiency areas in Austria.[9]



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