Diagnostic performance of ultrasound-based risk-stratification systems for thyroid nodules: Comparison of the 2015 American thyroid association guidelines with the 2016 Korean thyroid association/Korean society of thyroid radiology and 2017 American congress of radiology guidelines

Purpose: The aim of this study was to compare the diagnostic performance of ultrasound (US)-based risk-stratification systems for thyroid nodules in the 2015 American Thyroid Association (ATA) guidelines with those of the 2016 Korean Thyroid Association (KTA)/Korean Society of Thyroid Radiology (KSThR) and 2017 American Congress of Radiology (ACR) guidelines. Methods: From June 2013 to May 2015, a total of 902 consecutive thyroid nodules were enrolled in four institutions, and their US features were retrospectively reviewed and classified using the categories defined by the three guidelines. The malignancy risk of each category, as defined by all three risk-stratification systems, was calculated, and the diagnostic performance of the fine-needle aspiration (FNA) indications of the ATA guidelines were compared to those of the KTA/KSThR and ACR guidelines. Results: Of all nodules, 636 (70.5%) were benign and 266 (29.5%) malignant. The calculated malignancy risks for ATA categories 5, 4, 3, 2, and 1 nodule(s) were 71.7, 21.5, 2.6, 3.8, and 0%. Of all nodules, 7.6% (69/902) did not meet the ATA pattern criteria, but the malignancy risk was calculated to be 10.1% (7/69). The ATA guidelines afforded significantly higher diagnostic sensitivity (95.0%) than the ACR guidelines (80.2%; p = 0.001) but a lower specificity (38.1 vs. 68.9%; p < 0.001). On the other hand, the ATA guidelines exhibited a lower diagnostic sensitivity than the KTA/KSThR guidelines (100.0%; p = 0.07) but a higher specificity (28.2%; p < 0.001). The unnecessary FNA rate was the lowest when the ACR guidelines were used (25.8%), followed by the ATA (51.2%) and KTA/KSThR (59.4%) guidelines. Conclusion: The 2015 ATA guidelines afford relatively moderate sensitivity and an unnecessary FNA rate for thyroid cancer detection compared to the 2016 KTA/KSThR and 2017 ACR guidelines. US practitioners require a deep understanding of the benefits and risks of the US-based FNA criteria of different guidelines and potential impact on the diagnosis of low-risk thyroid cancers.