What is the role of embryology in the pathophysiology of pediatric omphalocele and gastroschisis (abdominal wall defects)?

Updated: Nov 05, 2019
  • Author: James G Glasser, MD, MA, FACS; Chief Editor: Dharmendra J Nimavat, MD, FAAP  more...
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Answer

Following fertilization, cellular division generates a hollow sphere, bisected by a bilaminar plate composed of epiblast and hypoblast, which abut the amnion and yolk sac cavities respectively. [7] The epiblast cells form the embryo; the hypoblast develops into the placenta. The bilaminar disc is divided axially by the primitive streak, at the apex of which is the primitive node. Epiblast cells pour into the primitive node, converting the bilaminar disc into a disk with three germ cell layers. Invagination occurs along the primitive streak, giving the embryo (in cross-section) the appearance of an omega. The curved portion of the omega fuses, forming the neural tube (central nervous system [CNS]) and displacing the notochord ventrally. The pinched-off tissue, dorsal to the neural tube, becomes epiderm. Laterally, the mesoderm undergoes differentiation: para-axial (peripheral nervous system), intermediate (gonads and kidneys), and lateral, which further divides into splanchnic (gastrointestinal [GI] tract) and somatic (body wall). The splanchnic mesoderm and endoderm fuse ventrally to form a tube (the GI tract); the somatic mesoderm and epiderm layers fuse anteriorly forming the anterior body wall and abdominal cavity (intraembryonic coelom). The embryo is surrounded by amnion, which encloses the extra-embryonic coelom. [8]

During the sixth week of development, rapid growth of the liver and intestines causes herniation of the midgut into the amniotic cavity. By the 10th week, the abdominal cavity is sufficiently large to accommodate return of the midgut. Rotation and fixation of the proximal and distal midgut (duodenum and ascending colon) occurs upon their return.

As the hindgut elongates, ingrowth of mesoderm forms the urorectal septum. Mesoderm also invades the cloacal membrane, uniting the genital tubercles and creating the urogenital sinus.

The body folds unite where the amnion invests the yolk sac and body stalk. Fusion is a complex process: A surface glycoprotein promotes adhesion between opposing segments of the nascent body wall; migration and apoptosis (planned cellular death) knit together the cephalic, caudal, and lateral folds about the attenuated yolk sac, causing constriction of the umbilical ring.


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