Fetal megacystis

Last revised by Satish Kumar Gupta on 16 Sep 2023

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

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

Associated anomalies are common 6 and include:

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

It is generally defined as a bladder diameter of:

  • >7 mm in the 1st trimester 3

  • >30 mm in the 2nd trimester ref

  • >60 mm in the 3rd trimester ref

Ancillary sonographic findings:

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.

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