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 <5mm), group 2 (5mm nodule size <10mm), group 3 (10mm nodule size <20mm), and group 4 (nodule size 20mm). 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 5mm in maximum diameter.