It is a severe anomaly and predominantly affects males. It is charcacterised by the exposure and protrusion of the mucosal surface of the posterior wall of the bladder to the exterior. It results due to the failure of the anterior abdominal wall and the anterior wall of the bladder to develop properly. Clinically it is associated with urinary drainage to the exterior and epispadias.
Exstrophy of bladder, available at: http://www.lucinafoundation.org/birthdefects-bladderextrophy.html
It occurs when a remnant of the allantois persists, thereby forming a fistula or a cyst. It is found along the midline, from the umblicus to the apex of the bladder. A urachal fistula is a direct conection between the bladder and the outside of the body at the umblicus, causing urinary discharge from the umbilicus.