Interobserver variability and diagnostic performance in US assessment of thyroid nodule according to size.

PURPOSE: To evaluate the interobserver variability for US assessments of thyroid nodules and analyze the diagnostic performances of US assessments in thyroid nodules according to nodule size. MATERIALS AND METHODS: This was an IRB-approved retrospective study with waiver of informed consent. A total of 400 surgically-confirmed thyroid nodules were included. Nodules were divided into 4 groups by size; group 1 (nodule size < 5 mm), group 2 (5 mm ≤ nodule size < 10 mm), group 3 (10 mm ≤ nodule size < 20 mm), and group 4 (nodule size ≥ 20 mm). Three experienced (7 - 10 years) radiologists retrospectively reviewed the US images. Agreement of each US descriptor and final US assessment, and diagnostic performances were calculated in each group and compared. RESULTS: Composition represented substantial or good agreement (k = 0.719 - 0.89). Margin showed the lowest agreement (k = 0.322 - 0.365). Individual kappa values for final assessment according to nodule size were as follows: group 1 (k = 0.674), group 2 (k = 0.596), group 3 (k = 0.674), and group 4 (k = 0.673). Specificity, PPV, and accuracy were significantly different among the groups with different size (p value < 0.05) and lowest in group 1. NPV, specificity, PPV and accuracy except PPV of observer 3 increased with nodule size (p < 0.05). CONCLUSION: Interobserver agreements were relatively good (k = 0.637) in final US assessment regardless of nodule size in experienced radiologists. High false-positive rate was observed in US assessment in nodules less than 5 mm in maximum diameter.