CAN the AMERICAN THYROID ASSOCIATION, K-TIRADS, and ACR-TIRADS ULTRASOUND CLASSIFICATION SYSTEMS BE USED to PREDICT MALIGNANCY in BETHESDA CATEGORY IV NODULES?

Objective: Management of thyroid nodules with Bethesda category III and IV cytology on fine needle aspiration (FNA) is challenging as they cannot be adequately classified as benign or malignant. Ultrasound (US) patterns have demonstrated the utility in evaluating the risk of malignancy (ROM) of Bethesda category III nodules. This study aims to evaluate the value of 3 well-established US grading systems (American Thyroid Association [ATA], Korean Thyroid Imaging Reporting and Data System [Korean-TIRADS], and The American College of Radiology Thyroid Imaging Reporting and Data System [ACR-TIRADS]) in determining ROM in Bethesda category IV nodules. Methods: Ninety-two patients with 92 surgically resected thyroid nodules who had Bethesda category IV cytology on FNA were identified. Nodule images were retrospectively graded using the 3 systems in a blinded manner. Associations between US risk category and malignant pathology for each system were analyzed. Results: Of the 92 nodules, 56 (61%) were benign and 36 (39%) were malignant. Forty-seven per cent of ATA high risk nodules, 53% of K-TIRADS category 5 nodules, and 50% of ACR-TIRADS category 5 nodules were malignant. The ATA high-risk category had 25% sensitivity, 82% specificity, 47% positive predictive value (PPV) for malignancy. K-TIRADS category 5 had 25% sensitivity, 85% specificity, 53% PPV for malignancy. ACR-TIRADS category 5 had 25% sensitivity, 84% specificity, 50% PPV for malignancy. None of the 3 grading systems yielded a statistically significant correlation between US risk category and the ROM (P =.30,.72,.28). Conclusion: The ATA, Korean-TIRADS, and ACR-TIRADS classification systems are not helpful in stratifying ROM in patients with Bethesda category IV nodules. Clinicians should be cautious of using ultra-sound alone when deciding between therapeutic options for patients with Bethesda category IV thyroid nodules. Abbreviations: ACR-TIRADS = The American College of Radiology Thyroid Imaging Reporting and Data System; ATA NSP = American Thyroid Association nodule sonographic patterns and risk of malignancy classification system; FN = follicular neoplasm; FNA = fine needle aspiration; FTC = follicular thyroid carcinoma; FVPTC = follicular variant of papillary thyroid carcinoma; HCC = Hurthle cell carcinoma; HCN = Hurthle cell neoplasm; K-TIRADS = Korean Thyroid Imaging Reporting and Data System; NIFTP = noninvasive follicular thyroid neoplasm with papillary-like nuclear features; NPV = negative predictive value; PPV = positive predictive value; ROM = risk of malignancy; US = ultrasound