Adnexal Lesions Pregnancy: Ultrasound Findings

A SYSTEMATIC review found that ultrasound could reliably assess adnexal lesions in pregnancy, with most lesions proving benign while malignant lesions remained uncommon. Adnexal lesions are abnormalities arising near the uterus, including ovarian cysts and tumours, and are commonly identified during pregnancy.

Malignancy in the general obstetric population was reported at 1 in 12,000 to 1 in 47,000 pregnancies. This makes accurate preoperative assessment important, as non-obstetric surgery during pregnancy was associated with miscarriage, preterm birth and increased maternal anaesthetic complications.

Decidualised Endometriomas Created a Diagnostic Challenge

The review included 16 studies involving 1,674 patients and 1,660 adnexal lesions. Among 1,379 patients from studies that did not exclusively report benign lesions, 93.1% had benign lesions, compared with 3.4% with borderline ovarian tumours (BOTs) and 3.5% with malignant lesions.

Most studies were retrospective and ultrasound-based. Simple cysts were the most common benign lesions, followed by mature cystic teratomas and endometriomas. Malignant lesions were most often epithelial ovarian cancers or metastases.

Borderline ovarian tumours and malignant lesions retained imaging features comparable with those seen in non-pregnant women. However, decidualised endometriomas (DEs) could resemble BOTs. Decidualisation was reported in 11.8–39.5% of endometriomas.

Both DEs and BOTs were often unilocular-solid and highly vascular. BOTs tended to be larger, with a median size of 88.0 mm versus 48.1 mm for DEs. Most DEs had one to three papillary projections, while most BOTs had more than three.

IOTA Models Showed Promise for Risk Assessment

Diagnostic models, including the International Ovarian Tumor Analysis two-step strategy and Assessment of Different NEoplasias in the adneXa model, showed specificity of 70.0–90.2% and negative predictive values of 90.0–98.3%. Their performance was limited by DEs being misclassified as malignant.

Transvaginal and transabdominal ultrasound remained the recommended first-line imaging approaches throughout pregnancy, although the gravid uterus could compromise views at more advanced gestations. Where ultrasound was inconclusive, diffusion-weighted MRI could improve diagnostic yield and offered a suitable second-line investigation.

The review highlighted a need to refine diagnostic tools, particularly for lesions containing solid components. Better differentiation between decidualised endometriomas, borderline ovarian tumours and malignant lesions could support more accurate risk assessment and help clinicians navigate management decisions while limiting unnecessary intervention during pregnancy.

However, the evidence base had limitations: most studies were retrospective and ultrasound-based, and substantial heterogeneity meant that model performance could not be combined in a meta-analysis. Further research will therefore be needed to establish how refined imaging criteria and diagnostic models perform across different pregnancy settings.

Reference

Cooper N et al. Diagnostic imaging of adnexal lesions in pregnancy: a systematic review. Ultrasound Obstet Gynecol. 2026;DOI:10.1002/uog.70296.

Featured image: Елена Бутусова on Adobe Stock