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Fetal megacystis

Fetal megacystis refers to the presence of an unusually large bladder in a fetus. 

The estimated incidence of antenatal imaging is at ~1:1500 pregnancies.

It can result from a number of causes but the main underlying mechanism is either distal stenosis or reflux.

Associated anomalies are common 6 and include:

It is generally defined as:

  • bladder diameter >7 mm in the first trimester 3
  • bladder diameter >30 mm in the second trimester reference required
  • bladder diameter >60 mm in the third trimester reference required

The overall prognosis can be variable from progressive obstruction to spontaneous resolution. A follow-up ultrasound is necessary to correctly interpret the significance of megacystis detected in the first trimester.

If the fetus is chromosomally normal and there is megacystis on the 1st trimester scan:

  • there is a spontaneous resolution of the megacystis in about 90% of cases when the 1st trimester longitudinal bladder diameter is between 7-15 mm 4
  • if the bladder diameter is >15 mm, there is a very high likelihood of progressive obstructive uropathy 4

Management will depend on the underlying pathology.

Article information

rID: 13417
Tag: cases, cases
Synonyms or Alternate Spellings:
  • Antenatal megacystis
  • Megacystis
  • Fetal megabladder

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Cases and figures

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