Meanwhile, the endoderm migrates to the center of this cylinder.By the fourth week of gestation the umbilical ring is formed. During the 6th week the midgut rapidly grows from the endoderm which causes a herniation of the gut through the umbilical ring. The gut rotates as it re-enters the abdominal cavity which allows for the small intestine and colon to migrate to their correct anatomical position by the end of the 10th week of development. This process fails to occur normally in cases of exomphalos, resulting in abdominal contents protruding from the umbilical ring.Gut contents fail to return to the abdomen due to a fault in myogenesis (muscle formation and migration during embryogenesis). During embryogenesis the mesoderm that forms muscle divides into several somites that migrate dorso-ventrally towards the midline. The somites develop three parts that are sclerotome which will form bone, dermatome which will form skin of the back and myotome which will form muscle. The somites that remain close to the neural tube at the back of the body have epaxial myotome, whilst the somites that migrate to the midline have hypaxial myotome. The hypaxial myotome forms the abdominal muscles. The myotome cells will give rise to myoblasts (embryonic progenitor cells) which will align to form myotubules and then muscle fibers. Consequently, the myotome will become three muscle sheets that form the layers of abdominal wall muscles. The muscle of concern for exomphalos is the rectus abdominis.
The exomphalos sac is kept warm and covered with a moist saline gauze and plastic transparent bowel bag to prevent fluid loss. The neonate also requires fluid, vitamin K and antibiotic administration intravenously. After management strategies are applied, a baby with an intact sac is medically stable and does not require urgent surgery. This time is used to assess the newborn to rule out associated anomalies prior to surgical closure of the defect. Studies show there is no significant difference in survival between immediate or delayed closure.Surgery can be performed directly for small omphaloceles, which will require a short stay in the nursery department, or in a staged manner for large omphaloceles, which will require several weeks stay. Staged closure requires a temporary artificial holding sac (a silo) to be placed over the abdominal organs and sutured to the abdominal wall. This can be made of non-adhesive dressing. The silo is gradually reduced in size at least once daily until all of the viscera have been returned to the abdominal cavity. This is repeated for several days to a week until surgical closure of the fascia/skin can be done. Closure may require a patch that can be rigid or non-rigid and made of natural biomaterials such as a bovine pericardium or artificial materials. The skin is then closed over the patch and it is re-vascularised by the bodys liver blood vessels post-surgery. The staged surgery is required, as rushed reduction of the exomphalos compromises venous return and ventilation, as it raises intra-abdominal pressure.