Real-world agreement in the ultrasound classification of subcapsular thyroid nodules: comparison with expert...

Ultrasound (US) is the most accurate tool for the assessment of thyroid nodules (TNs). Despite the subcapsular position of TNs may represent a game changer for clinical practice in selecting cases for biopsy or surgery, this parameter is not included in US-based risk stratification systems. The present study evaluated the agreement of endocrinologists using US in clinical practice with the experts' results employed as reference standard.

A sub-series of TNs for which the agreement between US expert endocrinologists and radiologists was perfect was assumed as reference. Participants of the 2025 Thyroid Update of Associazione Medici Endocrinologi (AME) were asked to assess TNs in a 3-choice answer: subcapsular, non-subcapsular, or uncertain. The agreement was determined according to majority consensus (i.e., ratings > 50% = final consensus outcome) and Fleiss κ (from 0.1 to 1.0).

The series included 13 TNs (6/13 cancer, 7/13 echographically at high risk) whose median distance from the anterior and posterior thyroid capsule was 0 and 1.5 mm, respectively. One hundred and six endocrinologists (females, 62%; age, < 40 years 33%; specialized professionals, 81%) participated as raters. The TNs assessed by experts as subcapsular were judged as subcapsular in 90% to 97% of votes. The TNs assessed as non-subcapsular by experts were classified as non-subcapsular by 3% to 48% of votes. The majority consensus fully matched the experts' assessment (κ = 1.0, p = 0.0003). The distance from the anterior thyroid capsule was an independent factor of assessment (p = 0.005, R² = 0.86).

Clinical endocrinologists largely agree with experts' assessment in subcapsular cases where experts had perfect concordance while uncertainty is present for non-subcapsular nodules. Future studies should establish a standardized definition of subcapsular TN.