Prospective Validation of Accuracy of American College of Radiologists- Thyroid Imaging Reporting and Data System (ACR-TIRADS) in Diagnosing Malignancy in Thyroid Nodule and a Prediction Score (TiPS) for Thyroid Malignancy.

Introduction: Studies on diagnostic accuracy of revised ACR-TIRADS have been mostly retrospective and includes selection bias for surgery.

Methods: Consecutive subjects >12 years of age, with palpable or ultrasound-revealed thyroid nodule, were included in the study. Nodules of size >1 cm or TIRADS score 4 or 5 >5 mm underwent ultrasound-guided FNAC. All Bethesda 4, 5 and 6 nodules underwent thyroidectomy. Patients with Bethesda 3 nodules were given options of close follow up or surgery.

Results: There were 253 benign (Bethesda 2), 23 malignant (Bethesda 6) and 41 indeterminate (Bethesda 3,4,5) nodules. Among 41 indeterminate nodules, 19 underwent surgery of which 14 were malignant. 295 nodules had a definitive outcome (defined as final outcome variable); which could be a benign cytology report or a histopathology report. Proportion of thyroid cancer was 12.5%. ACR-TIRADS had a sensitivity of 100% and specificity of 60.5%, considering final outcome variable as gold standard and ACR-TIRADS 1-3 as test negative and score 4-5 positive. Lower age and higher serum TSH level were associated with malignancy (P < 0.05). Predictive scoring system was formulated with age, TSH, ACR-TIRADS and Bethesda. Cumulative score of 6 (IQR 4.5- 6.5) or above had a sensitivity and specificity of 96.2%, and 97.5% respectively and negative predictive value of 99.5%.

Conclusion: Owing to high sensitivity, ACR-TIRADS can be considered as a good tool to rule-out malignancy, but not to predict the same due to lower specificity. Cumulative scoring system had high diagnostic accuracy for prediction of malignancy risk and can be a useful tool for selecting nodules for surgery.