omphalocele 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 MPheno.ontology exumbilication amniocele MP:0003052 Fyler:4404 exomphalos Do not confuse with umbilical hernia - caused by a failure to retract the umbilical hernia that occurs normally during development. abnormal abdominal wall morphology