Improving risk stratification of indeterminate adnexal masses on MRI: What imaging features help predict malignancy in O-RADS MRI 4 lesions?

•O-RADS MRI is a risk stratification system is for assessing adnexal masses.•Prevalence of malignancy in O-RADS MRI 4 lesions vary widely from 5 to 90%.•Imaging/clinical findings were different in malignant and benign O-RADS 4 lesions.•O-RADS MRI 4 lesions may be sub-stratified based on solid tissue and CA-125. Ovarian-Adnexal Reporting and Data System (O-RADS) MRI uses a 5-point scale to establish malignancy risk in sonographically-indeterminate adnexal masses. The management of O-RADS MRI score 4 lesions is challenging, as the prevalence of malignancy is widely variable (5–90%). We assessed imaging features that may sub-stratify O-RADS MRI 4 lesions into malignant and benign subgroups. Retrospective single-institution study of women with O-RADS MRI score of 4 adnexal masses between April 2021–August 2022. Imaging findings were assessed independently by 2 radiologists according to the O-RADS lexicon white paper. MRI and clinical findingswere compared between malignant and benign adnexal masses, and inter-reader agreement was calculated. Seventy-four women (median age 52years, IQR 36–61) were included. On pathology, 41 (55.4%) adnexal masses were malignant. Patients with malignant masses were younger (p=0.02) with higher CA-125 levels (p=0.03). Size of solid tissue was greater in malignant masses (p=0.01–0.04). Papillary projections and larger solid portion were more common in malignant lesions; irregular septations and predominantly solid composition were more frequent in benign lesions (p