VP04.12: Decidualised endometrioma versus borderline ovarian tumour: a difficult differential diagnosis during pregnancy

A 37-year-old patient with a previous history of endometriosis and hemicolectomy in the context of invaginated appendix due to an endometriotic lesion was diagnosed with a right adnexal mass on first-trimester ultrasound during pregnancy. On expert ultrasound at 16 weeks, a unilocular-solid mass was described, measuring 84x69x60 millimetres, with inhomogeneous low-level content and multiple round smooth papillary projections suggestive of decidualised endometrioma. A left ovarian mass with classic US endometrioma features and measuring 35x34x34 millimetres was also identified. Tumor markers were CA 125 34.4 U/mL and CA 19.9 11.1 U/mL. Considering the cyst morphology, the dimensions and homolateral persistent abdominal pain, it was not possible to exclude a borderline tumour, so a surgical approach was decided. She underwent a laparoscopic bilateral cystectomy, at 18 weeks of pregnancy, with a definitive pathology report describing markedly decidualised endometriomas. The pregnancy continued uneventfully until term. Endometrioma decidualisation during pregnancy (probably a progesterone effect) is an infrequent finding. Although ultrasonographic features of decidualised endometrioma can mimic a potential ovarian malignancy, a previously known endometrioma, and identification of smooth papillary contour on the adnexal mass can be very helpful for a more confident diagnosis of decidualisation. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.