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Grand Rounds

Fetal Megacystis: More than Just Lower Urinary Tract Obstruction?

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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

Standard 2nd Trimester Reference Library, Now Available on Your Phone with ObGFirst

Learn More  »

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