Ultrasonographic characteristics of medullary thyroid carcinoma according to nodule size: application of the Korean Thyroid Imaging Reporting and Data System and American Thyroid Association guidelines

Abstract

Background Few studies have categorized ultrasound (US) findings of various sized medullary thyroid carcinomas (MTCs) according to updated guidelines. Purpose To evaluate and compare the differences in US findings of MTC according to nodule size, using the Korean Thyroid Imaging Reporting and Data System (K-TIRADS) and American Thyroid Association (ATA) guidelines. Material and Methods The study included 119 patients with 129 MTC nodules, which were surgically confirmed at our institution between March 1999 and September 2017. Nodules were divided into large (≥1.0 cm) and small (<1.0 cm) groups. US images were analyzed according to the K-TIRADS and ATA guidelines. The differences in US characteristics between small and large nodules were compared using Fisher’s exact or Chi-square tests. Results Of 129 MTC nodules, 84 (65.1%) were large nodules and 45 (34.9%) were small nodules. According to the nodule size, small MTC nodules were classified more commonly as high suspicion by K-TIRADS and ATA (95.6% and 93.3%, respectively) ( P < 0.001), but presented neither cystic change, isoechogenicity, nor low suspicion category by K-TIRADS and ATA. In contrast, large MTC nodules showed more frequently cystic change (15.5%), isoechogenicity (16.7%), smooth margins (50%), or low or intermediate suspicion US features by K-TIRADS and ATA (59.6% and 36.0%, respectively) (all P values < 0.001). Conclusion Most small MTC nodules are classified as high suspicion on US, whereas large MTC nodules are diagnosed more frequently as low or intermediate suspicion by K-TIRADS and ATA.