A
urachal fistula is a
congenital disorder caused by the persistence of the
allantois (later,
urachus), the structure that connects an embryo's
bladder to the
yolk sac. Normally, the urachus closes off to become the
median umbilical ligament; however, if it remains open,
urine can drain from the bladder to an opening by the
umbilicus.
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