OP31.06: Decidualisation of endometriotic lesions in pregnancy

Endometriosis affects approximately 10% of premenopausal women. Ultrasound features of endometriosis in non-pregnant women are well described. There is paucity of data regarding prevalence and morphological appearances of endometriosis in pregnancy. This study examined a large number of women with pelvic endometriosis in pregnancy. We examined endometriotic lesions for signs of decidualisation and assessed the frequency of changes, accounting for lesion type and site. We searched our clinic database to identify all pregnancies with concomitant endometriosis on ultrasound scan. Vascularity of lesions was assessed by ultrasound Doppler examination. Endometriomas were defined as ovarian cysts filled with hyperechoic fluid and surrounded by healthy ovarian tissue. Endometriotic nodules were solid, hypoechoic lesions within the recto-sigmoid colon, rectovaginal septum, uterosacral ligaments or on the pelvic peritoneum, which were fixed on palpation. Features suggestive of ovarian decidualisation were thick irregular inner wall, papillary projections and high vascularity on Doppler examination. Decidualised endometriotic nodules were hyperechoic with moderate to high vascularity. We identified 85 women with pelvic endometriosis on early pregnancy scan between March 2008 and February 2017. The median maternal age was 35 years (range 22-45). 64/85 were nulliparous and 15/85 conceived using assisted reproductive technology. The median gestational age at presentation was 7+2 weeks (range 4+0–19+3). 69/85 women were diagnosed with endometriomas [n=111 cysts], 27/85 with endometriotic nodules [n=52 nodules] and 11/85 had both cysts and nodules. 8/111(7.2%) endometriomas showed sonographic features suggestive of decidualisation compared to 12/52(23.1%) endometriotic nodules (P=0.004). In 7/8 women with multiple lesions and decidualisation, all lesions were affected. Decidualised endometriosis in pregnancy is relatively common and may mimic pelvic malignancy. All sonologists should be familiar with these changes to avoid false positive diagnosis of malignancy and unnecessary surgical intervention.