Diagnostic imaging of adnexal lesions in pregnancy: systematic review.

objectiveTo describe the imaging features of adnexal lesions during pregnancy and assess the performance of current models for the risk assessment of such lesions.

methodsThis was a PROSPERO-registered systematic review including studies published from inception to 1 August 2025 and was performed as per Preferred Reporting Systems for Systematic Reviews and Meta-Analysis guidance using Covidence software. Studies were included if they utilized an objective or standardized assessment of imaging features (based on the International Ovarian Tumor Analysis (IOTA) terms and definitions, or predefined categorical variables), expert description or quantitative data (such as lesion measurements and number of papillary projections) to assess the risk of adnexal lesions during pregnancy. Standardized extraction of imaging features was performed and classification of outcomes was based on histology, resolution or expert impression. Diagnostic model performance was also extracted. Meta-analysis of model performance was not performed owing to study heterogeneity.

resultsOverall, 3349 studies were screened, of which 40 underwent full-text review and 16 were included in the systematic review, comprising 1674 patients and 1660 adnexal lesions. Most included studies were retrospective and ultrasound-based. Excluding six studies that exclusively reported benign lesions, 93.1% (1284/1379) of patients had benign lesions, 3.4% (47/1379) had borderline ovarian tumors (BOTs) and 3.5% (48/1379) had malignant lesions. Excluding studies reporting exclusively on endometrioma, the most common benign adnexal lesions were simple cysts (39.0% (393/1007)), mature cystic teratomas (24.2% (244/1007)) and endometriomas (14.9% (150/1007)). Malignant lesions were most often epithelial ovarian cancer or metastases. Both BOTs and malignant lesions retained imaging characteristics comparable with those observed in non-pregnant women. Decidualization was present in 11.8-39.5% of reported endometriomas. While decidualized endometriomas (DEs) and BOTs typically share characteristics, experts noted distinguishing morphological features and behaviors. BOTs were larger (median, 88.0 mm vs 48.1 mm), and although both were predominantly unilocular-solid lesions, BOTs were relatively more often multilocular-solid (30.0% vs 22.4%) compared with DEs. Both showed high vascularity, with most cases having a color score of 3. Most DEs (83.9%) had one to three papillary projections, whereas most BOTs (66.7%) had more than three papillary projections. Diagnostic models, such as the IOTA two-step strategy and the Assessment of Different NEoplasias in the adneXa model alone, showed high specificity (70.0-90.2%) and negative predictive value (90.0-98.3%), but performance was limited by misclassification of DEs as malignant.

conclusionsUltrasound can reliably assess adnexal lesions in pregnancy. DEs and BOTs can appear similar owing to their morphological overlap. Both BOTs and malignant lesions in pregnancy show morphology comparable with that in non-pregnant women, and IOTA models maintain a high negative predictive value for excluding malignancy in such cases. Future research should refine diagnostic tools to improve the differentiation of benign from malignant cysts with solid components. © 2026 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.