abnormal extraembryonic tissue morphology abnormal visceral yolk sac cavity morphology 2011-06-23T01:59:48Z MP:0011201 MPheno.ontology abnormal yolk sac cavity any structural anomaly of the closed space containing the yolk, formed by the fusion of the edges of the embryonic epiblast (hypoblast) and later surrounded by the visceral yolk sac (hypoblast and visceral yolk sac mesoderm) csmith