Fetal megacystis: a lot more than LUTO

OBJECTIVE: Megacystis represents a challenge in terms of counseling and management due to its various etiology and evolution. The aim of this study is to present a comprehensive overview of the underlying etiologies and structural anomalies associated with fetal megacystis. METHODS: This was a retrospective multicenter study carried out at the Fetal Medicine Units (FMUs) of the eight Academic Hospitals in the Netherlands. For each case referred to one of these centers due to fetal megacystis, data and measurements of fetal urinary tract and associated structural anomalies were collected. All available postmortem examinations and postnatal investigations were reviewed in order to establish the final diagnosis. In the first trimester, fetal megacystis was defined as a bladder with a longitudinal diameter (LBD) ≥ 7 mm, and in the 2nd and 3rd trimester as an enlarged bladder failing to empty during an extended US examination lasting at least 40 minutes. RESULTS: Out of 541 megacystis, megacystis was isolated (or merely accompanied by other signs of LUTO) in 360 cases (66%); and associated with other abnormal ultrasound findings in 181 cases (34%). The most common associated anomaly was an increased nuchal translucency (NT22%), followed by SUA and cardiac defects (10%). A final diagnosis was established in 418 cases, including 222 cases with isolated LUTO (53%) and 60 infants (14%) with normal micturition or isolated urological anomalies. In the remaining 136 cases (33%), a genetic syndrome, developmental or chromosomal abnormality was diagnosed. In total, 40 chromosomal abnormalities were diagnosed, including: Trisomy 18 (n = 24), Trisomy 21 (n = 5), Turner syndrome (n = 5), Trisomy 13 (n = 3) and deletion 22q11 (n = 3). Thirty-two cases presented with Ano-Rectal Malformations involving anus, rectum and urogenital tract. In cases with confirmed urethral and anal atresia, megacystis occurred early in pregnancy and the bladder appeared severely distended (the longitudinal diameter was equal or greater than twice the gestational age). Fetal macrosomia was detected in 6 cases and an overgrowth syndrome was detected in other 4 cases: 2 infants with Beckwith-Wiedemann and 2 infants with Sotos syndrome. Megacystis-microcolon-intestinal hypoperistalsis syndrome was diagnosed in five cases (1%) and prenatally suspected only in one case. CONCLUSIONS: Although the main cause of megacystis is LUTO, an enlarged fetal bladder can also be present as corollary finding of miscellaneous genetic syndromes, developmental disturbances and chromosomal abnormalities. This study provides an overview of the structural anomalies and congenital disorders associated with megacystis and proposes a flowchart for the differential diagnosis of genetic syndromes, chromosomal and developmental abnormalities, focusing on the morphological examination of the fetus. This article is protected by copyright. All rights reserved.