Introduction/Background The purpose of this study was to evaluate the Ovarian-Adnexal Reporting Data System Magnetic Resonance Imaging (O-RADS MRI) score for risk stratification of sonographically indeterminate adnexal masses.

Methodology Thirty-four patients with sonographically indeterminate adnexal mass according to Simple Rules were enrolled between March 2020 and March 2021. Subjective impression of risk of malignancy at ultrasound (US) examination by an experienced sonographer in the field and a pelvic MRI were performed. MRI included morphological, functional sequences and O-RADS MRI score (from 1 to 5: 1, nonadnexal lesion; 2, almost certainly benign; 3, low risk; 4, intermediate risk and 5, high risk). Patients were enrolled to surgery and the US and MRI results were compared to the reference standard (histopathological report).

Results In 34 patients enrolled, 21 (61.8%) had a benign ovarian mass, 6 (17.6%) borderline ovarian tumour and 7 (20.6%) ovarian cancer. At the US examination by an experienced sonographer 22 (64.7%) ovarian masses remained inconclusive at the US examination, 5 (41.7%) were classified correctly as benignant and 5 (41.7%) as malignant.The false positive and negative rates were both 16.7% for the experienced US examination. O-RADS MRI correctly classified as benign (score 2–3) 20 (58.8%) and as malignant (score 4–5) 10 (29.41%) ovarian masses. O RADS MRI showed a false positive rate of 5% and a false negative rate of 23% for the diagnosis of ovarian tumour risk of malignancy. O-RADS MRI showed an accuracy of 88%. Interestingly, in the subgroup of ovarian lesions inconclusive at the US expert examination (n=22), O-RADS MRI showed an overall accuracy of 100%.

Conclusion In this study, the O-RADS MRI score was accurate when stratifying the risk of malignancy in adnexal masses. O-RADS MRI score can be used to further characterise ovarian lesions indetermined by Simple Rules that remained inconclusive at US expert examination.