omphalocele Do not confuse with umbilical hernia - caused by a failure to retract the umbilical hernia that occurs normally during development. Fyler:4404 MP:0003052 MPheno.ontology amniocele exomphalos exumbilication protrusion of abdominal viscera at the base of the umbilical cord, with a covering membranous sac of peritoneum-amnion, that is caused by a severe body wall defect abnormal abdominal wall morphology