UNASSIGNED: Ultrasound-based risk stratification systems (Thyroid Imaging Reporting and Data Systems (TIRADSs)) of thyroid nodules (TNs) have been implemented in clinical practice worldwide based on their high performance. However, it remains unexplored whether different TIRADSs perform uniformly across a range of TNs in routine practice. This issue is highly relevant today, given the ongoing international effort to establish a unified TIRADS (i.e. I-TIRADS), supported by the leading societies specializing in TNs. The study aimed to conduct a direct comparison among ACR-, EU-, and K-TIRADS in the distribution of TNs: (1) across the TIRADS categories, and (2) based on their estimated cancer risk.
UNASSIGNED: A search was conducted on PubMed and Embase until June 2023. Original studies that sequentially assessed TNs using TIRADSs, regardless of FNAC indication, were selected. General study characteristics and data on the distribution of TNs across TIRADSs were extracted.
UNASSIGNED: Seven studies, reporting a total of 41,332 TNs, were included in the analysis. The prevalence of ACR-TIRADS 1-2 was significantly higher than that of EU-TIRADS 2 and K-TIRADS 2, with no significant difference observed among intermediate- and high-risk categories of TIRADSs. According to malignancy risk estimation, K-TIRADS often classified TNs as having more severe risk, ACR-TIRADS as having moderate risk, and EU-TIRADS classified TNs as having lower risk.
UNASSIGNED: ACR-, EU-, and K-TIRADS assess TNs similarly across their categories, with slight differences in low-risk classifications. Despite this, focusing on cancer risk estimation, the three TIRADSs assess TNs differently. These findings should be considered as a prerequisite for developing the I-TIRADS.

Ultrasound (US) is the pivotal procedure during the diagnostic work-up of thyroid nodule and several US-based risk stratification systems (RSSs) have been recently developed. Since the performance of RSSs in detecting medullary thyroid carcinoma (MTC) has been rarely investigated, the present systematic review aimed to achieve high evidence about (1) how MTC is classified according to RSSs; (2) if RSSs correctly classify MTC at high risk/suspicion, and (3) if MTC is classified as suspicious at US when RSSs are not used.
The review was performed according to MOOSE. The online search was performed by specific algorithm on January 2022. A random-effects model was used for statistical analysis.
Twenty-five papers were initially included and their risk of bias was generally low. According to ATA system, 65% of MTCs was assessed at high suspicion and 25% at intermediate suspicion. Considering all RSSs, a 54.8% of MTCs was put in a high-risk/suspicion category. Pooling data from studies without data of RSS the prevalence of ultrasonographically suspicious MTCs was 60%.
As conclusion, MTC presentation according to RSSs is partially known and it is classified in a high-risk/suspicion category of RSSs in just over a half of cases. This advises for further studies, ideally supported by international societies, to better define the US presentation of MTC.

Background: Several ultrasound (US)-based risk stratification systems have been increasingly used for the optimal management of thyroid nodules. However, there are considerable discrepancies across these systems. This study aimed to summarize and compare the category-based diagnostic performance in the detection of thyroid cancer of different US-based risk stratification systems from four societies: the American College of Radiology-Thyroid Imaging Reporting and Data System (ACR-TIRADS), the American Thyroid Association (ATA), the Korean Thyroid Association/Korean Society of Thyroid Radiology (KTA/KSThR; K-TIRADS), and the European Thyroid Association (EU-TIRADS). Methods: MEDLINE/PubMed and EMBASE databases were searched to identify original articles investigating the category-based diagnostic performance according to at least one of the following guidelines: ACR-TIRADS, ATA, K-TIRADS, and EU-TIRADS. Pooled sensitivity and specificity were calculated using a bivariate random-effects model. A subgroup analysis on nodules of 1 cm or larger and a meta-regression analysis to identify factors associated with the diagnostic performance were performed. Results: A total of 29 articles including 33,748 thyroid nodules met the eligibility criteria and were included in the analysis. For ACR-TIRADS, the pooled sensitivity and specificity were, respectively, 66% and 91% for category 5 and 95% and 55% for category 4 or 5. For ATA, the pooled sensitivity and specificity were, respectively, 74% and 88% for category 5 and 91% and 64% for category 4 or 5. For K-TIRADS, the pooled sensitivity and specificity were, respectively, 55% and 95% for category 5 and 89% and 64% for category 4 or 5. For EU-TIRADS, the pooled sensitivity and specificity were, respectively, 82% and 90% for category 5 and 96% and 52% for category 4 or 5. Study location, proportion of female patients and malignant nodules, and study design were associated with study heterogeneity. Conclusions: The overall diagnostic performance of the four US-based risk stratification systems was comparable.

Ultrasound (US) based classification systems exist for the stratification of thyroid nodules based on the risk for malignancy. This systematic review aimed to assess the evidence for the performance of US-based thyroid nodule classification systems through correlation with fine needle aspiration biopsy (FNAB). PubMed and Scopus were searched using keywords that included \'ultrasound classification\', \'thyroid nodules\', \'fine needle aspiration\', and \'malignancy\'. Inclusion criteria were as follows: studies/reviews reporting on US imaging for the classification of thyroid nodules. Exclusion criteria were as follows: no comparison between US imaging findings and histology reports based on FNAB, no full English text available/accessible. The database searches identified 66 publications. After evaluation, 12 studies met the inclusion criteria. Two US-based classification systems for thyroid nodules were assessed: the Thyroid Imaging Reporting and Data System (TIRADS) and the American Thyroid Association (ATA) guidelines. For TIRADS, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) ranged from 70.6% to 97.4%, 29.3% to 90.4%, 23.3% to 64.3%, and 87.1% to 99.0%, respectively. The median sensitivity, specificity, PPV, and NPV for TIRADS was 90.0%, 57.4%, 49.0%, and 91.0%, respectively. One study comparing TIRADS with the ATA guidelines demonstrated that TIRADS was superior in terms of sensitivity, whereas the ATA guidelines were superior in terms of specificity and PPV. The high sensitivity and NPV of the US-based TIRADS classification system have excellent utility for correctly classifying nodules as positive for malignant disease and for predicting the absence of malignant disease. The paucity of studies assessing the ATA guidelines highlights avenues for further research comparing TIRADS with other systems of thyroid nodule classification.