Ultrasound appearance of decidualized non-ovarian endometriotic lesions during pregnancy and after delivery.

OBJECTIVE: To evaluate the changes in the ultrasound characteristics of decidualized non-ovarian endometriotic lesions that occur during pregnancy and after delivery. METHODS: This was a prospective observational cohort study carried out at a single tertiary center between December 2018 and October 2021. Pregnant women with endometriosis underwent a standardized transvaginal ultrasound examination with color Doppler imaging once in every trimester and after delivery. Non-ovarian endometriotic lesions were measured and evaluated by subjective semiquantitative assessment of blood flow. Lesions with moderate-to-marked blood flow were considered decidualized. The size and vascularization of decidualized and non-decidualized lesions were compared between the gravid state and after delivery. Only patients with non-ovarian endometriotic lesion(s) who underwent postpartum examination were included in the final analysis. RESULTS: Overall, 26 pregnant women with a surgical or sonographic diagnosis of endometriosis made prior to conception were invited to participate in the study, of whom 24 were recruited. Of those, 13 women with non-ovarian endometriosis who attended the postpartum examination were included. In 7/13 (54%) cases, the lesion(s) were decidualized. In 4/7 (57%) women with decidualized lesion(s), the size of the largest lesion increased during pregnancy, while in 3/7 (43%), the size was unchanged. The size of non-decidualized lesions did not change during pregnancy. On postpartum examination, only seven lesions were observed, of which three were formerly decidualized and four were formerly non-decidualized. Lesions that were detected after delivery appeared as typical endometriotic nodules and were smaller compared with during pregnancy. The difference in maximum diameter between the gravid and postpartum states was statistically significant in decidualized lesions (P < 0.01), but not in non-decidualized lesions (P = 0.09). The reduction in mean diameter was greater in decidualized compared with non-decidualized lesions (P = 0.03). CONCLUSIONS: Decidualization was observed in 54% of women with non-ovarian endometriotic lesion(s) and resolved after delivery. Our findings suggest that the sonographic features of decidualization, which might mimic malignancy, are pregnancy-related and that expectant management and careful monitoring should be applied in these cases. Clinicians should be aware of the changes observed during pregnancy to avoid misdiagnosing decidualized lesions as malignancy and performing unnecessary surgery. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.