BACKGROUND AND PURPOSE:

• Fetal megacystis (a distended urinary bladder) is readily apparent on ultrasound
• Often accompanies lower urinary tract obstruction (LUTO) but may be associated with other anomalies
• Fontanella et al. (Ultrasound in Obstetrics & Gynecology, 2018) reviewed underlying etiologies and structural anomalies associated with fetal megacystis

METHODS:

• Retrospective multicenter study
  • Referral centers for fetal ultrasound anomalies including megacystis
• Data collection included
  • Measurements of fetal urinary tract
  • Associated structural anomalies
• Diagnosis: Postmortem and postnatal studies
• Fetal megacystis was defined as
  • First trimester: longitudinal bladder diameter (LBD) ≥ 7 mm
  • Second and third trimester: Enlarged bladder failing to empty during an extended ultrasound examination (min. 40 min)

RESULTS:

• 541 pregnancies included | 418 with confirmed final diagnosis
  • 222 (53%) were cases with isolated LUTO
  • 60 (14%) were infants with normal micturition or minor isolated urological anomalies
  • 136 (33%) were cases with a diagnosed developmental or chromosomal abnormality or genetic syndrome
• Fetal megacystis was
  • Isolated or involving no other structures beyond LUTO: in 67%
  • Other non-urinary findings: 33%
• Among other non-urinary findings, most common associated ultrasound anomalies included
  • Increased NT: 22%
  • Single umbilical artery (SUA): 10%
  • Congenital heart disease (CHD): 10%
  • VACTERL and OEIS (omphalocele, exstrophy, imperforate anus and spinal defect: 5%
• 40 chromosomal abnormalities were diagnosed
  • Trisomy 18: n = 24 (LUTO in 88% | Increased NT, CHD, omphalocele, skeletal anomalies)
  • Trisomy 21: n = 5 (LUTO in 60% | Increased NT, skeletal anomaly)
  • Turner syndrome: n = 5 (LUTO in 40% | Increased NT, umbilical cord cyst)
  • Trisomy 13: n = 3 (LUTO in 100% | CHD, SUA, polydactyly, cleft lip/palate)
  • 22q11 deletion: n = 3 (LUTO in 100% | CHD)
• 32 cases presented with anorectal malformations involving the anus, rectum, and urogenital tract
  • With urethral and anal atresia, megacystis appears early and is severe
• 6 cases presented with fetal macrosomia
  • 4 cases presented with an overgrowth syndrome
  • Beckwith–Wiedemann syndrome: 2 fetuses
  • Sotos syndrome: 2 fetuses
• Megacystis-microcolon-intestinal hypoperistalsis diagnosed in 1% (5 cases) following delivery, with only 1 prenatal consideration in differential 

CONCLUSION:

• Primary cause of fetal megacystis remains LUTO
  • Other birth defects and genetic syndromes may be associated with megacystis found on prenatal ultrasound
• The authors encourage a thorough structural exam to guide the diagnosis and look beyond the urinary tract, and include a flowchart to guide the differential diagnosis
  • Early diagnosis <18 weeks is especially worrisome for chromosomal anomalies and VACTERL (especially if associated spinal, renal, limb, CHD, SUA and umbilical cord cysts)

Learn More – Primary Sources:

Fetal megacystis: a lot more than LUTO

Related ObG Topics:

The Use of Microarrays in the Prenatal and Postnatal Setting – Current Professional Guidelines

Single Umbilical Artery, or the “Two Vessel Cord”: What Does it Mean? 

Chromosomal Microarrays and Abnormal Prenatal Ultrasound Findings

Can Whole-Exome Sequencing Help Diagnose Otherwise Unexplained Fetal Structural Anomalies?