Abstract: Thyroid nodules are common diseases in neck. As the most commonly used imaging technique for the evaluation of thyroid nodules, ultrasound has a high accuracy of differentiating malignant from benign thyroid nodules. However, there are inter-observer variabilities in the diagnosis and description of thyroid nodules by ultrasound. And terms used to describe nodules are often poorly defined, which is the major cause of inter-observer variabilities. Several authors have recently described a standardized risk stratification system called the Thyroid Imaging, Reporting and Data System (TI-RADS), modeled on the BI-RADS system for breast imaging. And then they recommended corresponding fine-needle aspiration (FNA) or follow-up according to risk stratification. Despite these efforts, none of these TIRADS classifications have been widely adopted. With the widely use of high-quality imaging, incidental thyroid nodules (ITNs), which are defined as nodules not previously detected or suspected clinically, are increasingly prevalent. Most ITNs are small and benign. And incidental thyroid malignancies typically have indolent behavior. There is no unified standard for clinical management of ITNs by now. As a result, American College of Radiology (ACR) formed the Incidental Thyroid Findings Committee and ACR TI-RADS Committee. They published “Managing ITNs Detected on Imaging: White Paper of the ACR Incidental Thyroid Findings Committee”, “Thyroid Ultrasound Reporting Lexicon: White Paper of the ACR TIRADS Committee” and “ACR TI-RADS: White Paper of the ACR TI-RADS Committee” from 2015 to 2017. Through establishing these white papers, ACR tried to provide guidance regarding management of thyroid nodules on the basis of their ultrasound appearance, standardize the diagnostic approach to thyroid nodules through the development of a lexicon and recommend a practical approach to managing ITNs on CT, MRI, nuclear medicine and ultrasound studies.

Key words: American College of Radiology, Thyroid Imaging, Reporting and Data System, Thyroid nodules, Incidental thyroid nodule