Original articleHealth services research and policyACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee
Introduction
Thyroid nodules are exceedingly common, with a reported prevalence of up to 68% in adults on high-resolution ultrasound [1]. Currently, fine-needle aspiration (FNA) is the most effective, practical test to determine whether a nodule is malignant or may require surgery to reach a definitive diagnosis [2]. However, most nodules are benign, and even malignant nodules, particularly ones smaller than 1 cm, frequently exhibit indolent or nonaggressive behavior 3, 4, 5. Therefore, not all detected nodules require FNA and/or surgery.
Despite a rapid increase in the reported incidence of papillary thyroid cancer that resulted from screening thyroid sonography in asymptomatic patients in South Korea, mortality has remained extremely low [6]. In the United States, overdiagnosis of thyroid cancer, defined as “diagnosis of thyroid tumors that would not, if left alone, result in symptoms or death” accounted for 70% to 80% of thyroid cancer cases in women and 45% of cases in men between 2003 and 2007 [7].
Therefore, a reliable, noninvasive method to identify which nodules warrant FNA on the basis of a reasonable likelihood of biologically significant malignancy would be highly desirable. In 2015, committees convened by the ACR published white papers that presented an approach to incidental thyroid nodules and proposed standard terminology (lexicon) for ultrasound reporting 8, 9. The purpose of the present white paper is to present our system for risk stratification, which is designed to identify most clinically significant malignancies while reducing the number of biopsies performed on benign nodules.
Section snippets
Project Rationale and Consensus Process
Several professional societies and groups of investigators have proposed methods to guide ultrasound practitioners in recommending FNA on the basis of ultrasound features 10, 11, 12, 13, 14, 15, 16, 17, 18. Some of these systems were termed TI-RADS (Thyroid Imaging, Reporting and Data System) because they were modeled on the ACR’s BI-RADS®, which has been widely accepted in breast imaging. Other societies, such as the American Thyroid Association (ATA), have taken a slightly different,
Overview of ACR TI-RADS
The ultrasound features in the ACR TI-RADS are categorized as benign, minimally suspicious, moderately suspicious, or highly suspicious for malignancy. Points are given for all the ultrasound features in a nodule, with more suspicious features being awarded additional points. Figure 1 presents these features arranged per the five lexicon categories [8]. When assessing a nodule, the reader selects one feature from each of the first four categories and all the features that apply from the final
Structure
To make the system easy to understand and apply, the ACR TI-RADS does not include subcategories, nor does it include a TR0 category to indicate a normal thyroid gland. The ACR TI-RADS also lends itself to implementation as templates in voice recognition reporting or computerized decision support systems. The committee decided against the pattern-based approach used by the ATA on the basis of the results of a study by Yoon et al [25], which showed that the ATA guidelines were unable to classify
ACR TI-RADS Feature Categories
In this section, we elaborate on the five groups of ultrasound findings, ACR TI-RADS levels, and size thresholds. Readers are encouraged to refer to the lexicon white paper for detailed descriptions of all the categories and features [8]. As well, any history of prior FNA or ethanol ablation should be sought, as these procedures may lead to a suspicious appearance at follow-up ultrasound [31].
Papillary Thyroid Microcarcinomas
The ACR TI-RADS is concordant with other guidelines in recommending against routine biopsy of nodules smaller than 1 cm, even if they are highly suspicious. However, because some thyroid specialists advocate active surveillance, ablation, or lobectomy for papillary microcarcinomas, biopsy of 5- to 9-mm TR5 nodules may be appropriate under certain circumstances 24, 55, 56, 57. The determination to perform FNA will involve shared decision making between the referring physician and the patient.
Measurement and Documentation
Accurate sizing of thyroid nodules is critical, as the maximum dimension determines whether a given lesion should be biopsied or followed. Although some interobserver discrepancy is inevitable because of variable conspicuity, consistent technique improves measurement accuracy and reproducibility.
Nodules should be measured in three axes: (1) maximum dimension on an axial image, (2) maximum dimension perpendicular to the previous measurement on the same image, and (3) maximum longitudinal
Future Directions
The committee believes that the ACR TI-RADS meets our stated goals, although acknowledging the limitations of our additive approach, which does not fully account for the possibility that the risk conferred by a given ultrasound feature may vary depending on what other features are present in a nodule. As well, several committee members have embarked on a parallel project in which interobserver variability of ultrasound feature assignment will be measured. We plan to revise the ACR TI-RADS
Take-Home Points
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The goal of this project is to define a risk stratification system for thyroid nodules (ACR TI-RADS) to guide decisions regarding FNA and follow-up.
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The ACR TI-RADS chart allows practitioners to assign points to nodules based on ultrasound features from a standardized lexicon that lends itself to structured reporting.
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The features that form the basis of this system will be assessed for inter-observer variability in a parallel project.
Acknowledgments
The authors thank Dr Herbert Chen, chair of the Department of Surgery at the University of Alabama at Birmingham, for reviewing the manuscript. We also are grateful to Dr Xuan V. Nguyen of Ohio State University for performing the SEER data analysis.
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Dr Berland received personal fees from Nuance Communications during the conduct of the study. Dr Beland has received personal fees from Hitachi Aloka America outside the submitted work. All other authors have no conflicts of interest related to the material discussed in this article.