Urachus

The allantois develops as a outgrowth of the cloaca. Thus the embryonic urinary bladder is connected to the allantoic cavity by a patent (open) duct through which urine can flow. The connection between bladder and allantois within the median ligament of the bladder is named: urachus (a Greek term).

Normally at birth, the urachus has degenerated and is evident only as a scar at the apex of the urinary bladder. Possible developmental anomalies include:
      • patent urachus (urachal fistula) urine dribbling through the open urachus keeps the umbilical area wet (A above);
      • vesical diverticulum (urinary bladder diverticulum) the proximal end of the urachus persists and may retain urine, predisposing the individual to chronic cystitis (B);
      • urachal sinus (urachal umbilical sinus) the distal end of the urachus remains patent and can be a site of infection and a source of drainage (B).

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