EP06.38: Pop‐off mechanisms in fetal megacystis: extravasation, umbilical cord cyst, ureterocele and mega‐ureter

This study aimed to comprehensively analyse incidence, antenatal characteristics and prognostic implications of three antenatal pop-off mechanisms, which might alleviate intraluminal pressure within the urinary tract, in fetuses with megacystis. This was a retrospective multicentre study across all academic centres in the Netherlands, including fetuses with suspected megacystis (N = 543). Three antenatal pop-off mechanisms were identified: Umbilical cord cysts (UCC) (n = 39), extravasation (n = 47), and mega-ureter/ureterocele (n = 39). The identification of an UCC was significantly associated with early-onset megacystis (OR 4.2), normal amniotic fluid index (AFI) (OR 3.26), associated congenital anomalies (OR 3.27) and the highest prevalence of complex diagnoses (50%), primarily due to anorectal malformations (67%). Extravasation of urine was correlated with severe megacystis (OR 2.7), abnormal AFI (OR 2.8), and associated congenital anomalies (OR 2.1). Mega-ureter/ureterocele was associated with late-onset megacystis (OR 4.0), a thickened bladder wall (OR 6.7) and lowest prevalences of associated congenital anomalies (22%). Regarding outcomes, intrauterine fetal demise (IUFD) was most prevalent in fetuses with UCC (15%), termination of pregnancy and neonatal death were most common in extravasation-associated cases, 50% and 17% respectively, while the majority of mega-ureter/ureterocele cases were born alive (72%). UCC was associated with early-onset megacystis, normal AFI, other congenital anomalies and the highest prevalences of IUFD, while the occurrence of urinary extravasation was associated with an antenatal clinical picture characterised by severe megacystis, abnormal AFI and other congenital anomalies and associated with high rates of pregnancy termination and neonatal death. A mega-ureter/ureterocele mainly occurred in late-onset and isolated megacystis showing a thickened bladder wall, low prevalences of other congenital anomalies and highest survival rates.