Looking through the keyhole at Fetal Megacystis

Maria Chaney Cahill, Univeristy College Dublin 


Megacystis is a sonographic feature of an abnormally large fetal bladder for gestational age. The incidence is estimated to be 0.38% globally with predominantly male fetuses affected. Even with treatment options and early diagnosis this condition has a relatively poor prognosis.

The fetal kidneys produce urine from around 10 weeks. During the first trimester from 10 14 weeks the normal sagittal diameter of the bladder is <7mm. A measurement above this is classified as megacystis. The diagnosis is made in the second and third trimester when there is an enlarged fetal bladder that fails to empty over a 45 minute period or a fetal bladder that measures >10% of the craniocaudal length of the fetus. The prognosis and outcomes of megacystis are varied because of the wide spectrum of aetiologies involving the kidneys and other structures of the urinary system. This following is a case of megacystis caused by lower urinary tract obstruction (LUTO).

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