An Interobserver Comparison of the Ultrasound Lexicon Classification of Thyroid Nodules: A Single-Center Prospective Validation Study

<b>Background/Objectives</b>: Guidelines for the risk stratification of thyroid nodules are based on certain well-recognized sonographic features of nodules. However, significant variations in reported sensitivity and specificity values are observed due to the overlap of imaging characteristics between benign and malignant nodules. Additionally, differences in ultrasound (US) equipment and the varying experience levels of radiologists performing the imaging procedures contribute to these discrepancies. Inevitably, there are also interobserver differences. The aim of this study was to investigate interobserver agreement on these criteria using the international thyroid imaging reporting and data system (I-TIRADS) thyroid evaluation framework, independently assessed by three residents and one consultant. <b>Methods</b>: We included 393 patients who underwent ultrasound-guided fine needle aspiration biopsy (FNAB) within four months. In each case, longitudinal and transverse video images of the thyroid gland, neck chain, and biopsied nodules were recorded. The evaluations of the parameters defined in the I-TIRADS dictionary were then performed by a radiologist with 15 years of experience and radiology assistants with 3, 3, and 2 years of experience, respectively, blinded to the images, pathology data, and patient demographics. The parameters evaluated included composition, echogenicity, margin, direction of growth, calcification, extension beyond the thyroid, and lymph node. An interobserver comparison between the US lexicon classifications of thyroid nodules was then performed. <b>Results</b>: The results of our study showed that the highest level of consensus was observed in the 'mixed predominantly cystic' classification, indicating a solid consistency between the assessors (κ = 0.729). Conversely, the subcategories 'Solid', 'Mixed Predominantly Solid' and 'Spongiform' showed moderate agreement, while the "Pure Cyst" subcategory exhibited the lowest level of agreement among the assessors (κ = 0.292). Agreement among the three radiology assistants was strong concerning the evaluation of nodule composition, growth direction, and lymph node assessment. In contrast, a moderate level of consensus was noted regarding the assessment of extrathyroidal extension, margins, and echogenicity. Notably, the parameter exhibiting moderate agreement across all readers was the presence of echogenic foci or calcifications. <b>Conclusions</b>: the reproducibility observed in the parameters defined within the lexicon supports its potential to enhance consistency and interobserver agreement in thyroid nodule assessment.