Comparison of Risk of Malignancy Index (RMI) and Ovarian-Adnexal Reporting and Data System (O-RADS) Score in Diagnostic Evaluation of Adnexal Masses: A Diagnostic accuracy study

Abstract

Background: Accurate preoperative differentiation between benign and malignant adnexal masses is essential for appropriate surgical planning and optimal patient outcomes. Ultrasound-based risk stratification systems such as the Ovarian-Adnexal Reporting and Data System (O-RADS) and biochemical-clinical models like the Risk of Malignancy Index (RMI) are commonly used for this purpose. Objectives: To evaluate and compare the diagnostic accuracy of O-RADS ultrasound classification and Risk of Malignancy Index-2 (RMI-2) in predicting malignancy in adnexal masses, using histopathology as the reference standard. Methods: This diagnostic accuracy study included 250 patients with adnexal masses who underwent preoperative ultrasonography and serum CA-125 estimation. Each lesion was classified according to O-RADS and RMI-2. All patients subsequently underwent surgical intervention, and histopathological diagnosis was obtained. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and receiver operating characteristic (ROC) curve analysis were calculated and compared. Results: Histopathology revealed 180 (72%) benign and 70 (28%) malignant lesions. O-RADS showed higher sensitivity (85.7%), specificity (83.3%), NPV (93.1%) compared to sensitivity, specificity and negative predictive value of RMI-2 (65.7%, 86.7% and 83.3%, respectively). ROC analysis revealed a significantly higher area under the curve for O-RADS (0.89) compared to RMI-2 (0.81) (p = 0.016). Conclusion: O-RADS demonstrates superior diagnostic performance over RMI-2 for preoperative risk stratification of adnexal masses and can be effectively adopted as a primary ultrasound-based assessment tool.