umbilical-urachal sinus umbilical-urachal sinus umbilical-urachal sinus is a congenital disorder of the urinary bladder caused by failure of obliteration of proximal or distal part of the allantois, and the presentation of this anomaly is more common in children and rarer in adults. umbilical-urachal sinusother namesurachal sinusspecialtyurology it is thought have been first described by cabriolus in 1550. complications infection, with possible abscess formation. concurrent occurrence of a tumour.