Ultrasound risk stratification systems for thyroid nodule: between lights and shadows, we are moving towards a new era

Ultrasound (US) has long played a major role in the assessment of thyroid nodules and their risk of malignancy, and its importance has been further enhanced over the past decade by the development of a number of US-based risk stratification systems (US-RSSs), referred to in some cases as TIRADS (Thyroid Imaging Reporting And Data Systems). The high-risk categories of all currently available US-RSSs display strong associations to cytological diagnostic classes of “malignant/suspicious-for-malignancy” and the low-risk classes are clearly associated to “not neoplastic/benign” cytology. The introduction of these systems has elevated the diagnostic performance of US to a level approaching that of fine-needle aspiration (FNA) cytology. The time seems ripe to exploit this new level of accuracy to reduce the number of FNAs for nodules likely to be benign (i.e., sonographically classified as low-risk with no suspicious clinical features). In the near future, US-RSS could also become the main tool for diagnosing papillary thyroid cancers. The establishment of a new “international TIRADS”—currently in progress—will be critical to guide us towards a new era.