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Background
Thyroid nodules are commonly encountered by radiologists. In 2017, the American College of Radiology assembled a committee to create the Thyroid Imaging Reporting and Data System (TI-RADS) for risk stratification of thyroid nodules to guide management and as a standardized lexicon to communicate results. The overall purpose was to determine whether nodules require fine needle aspiration (FNA) and to decrease the amount of benign nodules being biopsied. Radiology residents may find this algorithm complicated to navigate. This exhibit aims to guide them in assessing thyroid nodules and in using the TI-RADS lexicon to report results.

Educational Goals / Teaching Points
This exhibit will provide an overview of normal thyroid anatomy, basic ultrasound appearance, and useful search patterns. The TI-RADS feature categories will be discussed through a case-based review with imaging examples from our institution’s thyroid center to demonstrate the nuances of the lexicon. Management of nodules will be explored based on the respective TI-RADS score with examples of outcomes, including a brief explanation of the Bethesda scoring system for cases requiring FNA.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
There are five TI-RADS categories: composition, echogenicity, shape, margins, and echogenic foci. Each feature within a category has an assigned point value, with 0 points for benign features and up to 3 points for suspicious features. The likelihood of a nodule being malignant is directly proportional to the number of suspicious ultrasound features. Malignant nodules exhibit an average of 2 - 3 suspicious ultrasound findings. These include microcalcifications, hypoechogenicity, irregular or microlobulated contour, and a taller-than-wide shape. When multiple criteria are evaluated together, the specificity increases; thus, points are summed to give a nodule an overall TI-RADS score. TR1 and TR2 nodules are benign and do not require FNA. These include simple anechoic cysts, colloid cysts, and isoechoic spongiform nodules. TR3 nodules are mildly suspicious, TR4 nodules are moderately suspicious, and TR5 nodules are highly suspicious. Subsequent imaging follow-up and FNA recommendations for these nodules are based on their size. For nodules that do undergo FNA, pathologists utilize the Bethesda scoring system to report findings that help clinicians determine management. The Bethesda system describes six diagnostic categories including nondiagnostic (I), benign (II), atypia or follicular lesion of undetermined significance (III), follicular neoplasm or suspicious for follicular neoplasm (IV), suspicious for malignancy (V), and malignant (VI).

Conclusion
TI-RADS is a useful and standardized way to communicate thyroid nodule findings and to judicially determine which nodules warrant FNA and which require imaging follow-up. Though it may seem cumbersome to residents at first, a case-based review should be a helpful guide in solidifying their understanding of thyroid nodule management.