This was a 19  year old primi with history of consanguinity.The scan was done in the first trimester.
A large cystic mass was made out in the lower abdomen.

MULTI PLANAR VIEW OF FETUS SHOWING GROSSLY ENLARGED BLADDER

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The following text about mega cystis can be found in http://radiopaedia.org/articles/fetal-megacystis.

Fetal megacystis refers to the presence of an unusually large bladder in a fetus. It is generally defined as a

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

Epidemiology

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

Pathology

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

Associations

Associated anomalies are common ⁶ and include

• posterior urethral valves
• chromosomal anomalies
  • on a first trimester scan ( 10 – 14 weeks)
    • if the longitudinal bladder diameter of 7 – 15 mm there is a risk of a chromosomal defects is esimated at ~ 25% ⁴ 
    • if the bladder diameter is > 15 mm the risk of chromosomal defects is estimated at ~ 10% ⁴
• oligohydramnios
• megacystis microcolon intestinal hypoperistalsis (MMIH) syndrome (Berdon syndrome)
• megacystis megaureter syndrome
• prune belly syndrome

• Radiographic assessment

  Antenatal ultrasound

  Will show an enlarged bladder

  Ancilliary sonographic findings

  • may show evidence of oligohydramnios
  • may show associated renal anomalies

  Treatment and prognosis

  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 chromosmally normal and there is megacystis on the 1^st trimester scan

  • there is spontaneous resolution of the megacystis in about 90% of cases when the 1^sttrimester longitudinal bladder diameter is between 7 – 15 mm ⁴.
  • if the bladder diameter is > 15 mm there is a very high likelihood  of associated with progressive obstructive uropathy ⁴

  Management will depend on the underlying pathology