At the end of the fifth week of embryogenesis, the intra-embryonic mesoderm forms the axial part on both sides of the midline, the intermediate part, and the lateral plate. The space that is formed between the cells of the lateral plate delimits it into two layers: a layer of somatic mesoderm and a layer of mesoderm of the innards. The latter continues into the mesoderm of the wall of the yolk sac. The space between the aforementioned layers of the mesoderm makes up the intraembryonic celom (body cavity).
At first, the intraembryonic celom is directly connected to the extra-germinal cavity on both sides, but over time this connection disappears. The intra-embryonic cavity formed in this way extends from the thoracic to the pelvic area.
Defects in the body wall
Defects in the ventral wall of the body that occur both in the chest and in the abdominal area can cause heart defects, abdominal organs, and the genitourinary system. These defects can be the result of a violation of the folding processes of the embryo. In this case, the underdevelopment of one or several of the four folds (head, tail or two lateral), which normally ensure the formation of the ventral wall near the navel, causes a malformation of this wall. Another cause of this kind of defect may be a violation of the development of the embryo wall - muscles, bones, skin.
The sternum fissure - is a defect that occurs as a result of a violation of fusion along the midline of the two mesoderm plates from which this bone is formed. In the presence of sternum fissure or the absence of its lower third, the heart may protrude through this defect or even be outside the chest cavity (ectopy of the heart). Sometimes the defect extends to the abdominal wall, causing a whole range of disorders known as the Cantrell pentad, which connects the sternum fissure, ectopy of the heart, omphalocele, diaphragmatic hernia and congenital heart defects interventricular septal defect, Fallot tetrad. Ectopia of the heart occurs as a result of impaired development of the head and side folds.
Umbilical hernia (omphalocele) is a protrusion of the abdominal cavity through an enlarged umbilical ring. These organs, which may include the liver, small intestine, colon, stomach, spleen, bladder, are covered with amnion. The cause of umbilical hernia is the insolvency of the viscera to be drawn into the body cavity with their physiological protrusion during 6-10 weeks of development. This defect occurs with a frequency of 2.5 cases per 10,000 newborns and is accompanied by a high mortality rate (25%) and many other abnormalities, such as cardiac abnormalities (50%) и and neural tube developmental defects (40%). In approximately 50% of newborns with with omphalocele, chromosomal aberrations are detected.
Gastroschisis - is a protrusion of the insides through the defect of the abdominal wall directly into the amniotic cavity. A wall defect occurs lateral to the navel, usually on the right. The alvus are not covered by either the peritoneum or the amnion and can be damaged by amniotic fluid. In the case of omphalocele or gastroschis, the level of alpha-fetoprotein in the amniotic fluid is elevated, which can be determined prenatally.
Gastroschisis occurs with a frequency of 1 case per 10,000 newborns, and the number of children born with this defect increases. Unlike omphalocele, gastroschis is not accompanied by chromosomal aberrations, as well as other malformations, and therefore the possibility of survival of newborns with this defect is quite high. At the same time, twisting of the protruding intestines can lead to constriction of their blood vessels, gangrene of a significant segment of the intestine and fetal death.
Congenital diaphragmatic hernia is one of the most common developmental abnormalities (1 in 2,000 newborns). The cause of this defect is most often a violation of the process of closing the pericardial-abdominal canals with one or two pleuro-abdominal membranes. In this case, the peritoneal cavity and pleural cavities remain interconnected along the posterior wall of the body, and the organs of the abdominal cavity can penetrate into the pleural cavity. In 85-90% of cases, a congenital diaphragmatic hernia develops on the left side, and loops of the intestines, stomach, spleen, and even part of the liver can penetrate the chest cavity. As a result of this, the heart shifts forward, the lungs are compressed and remain underdeveloped. This defect is often incompatible with life (75% mortality) due to hypoplasia and lung dysfunction.
In some cases, the development of a small area of the muscle part of the diaphragm is impaired, and the hernia may remain unrecognized for several years of the child's life. Such a defect often occurs in the anterior portion of the diaphragm and is called a sternal hernia. In this case, a slight protrusion of the peritoneum, which may include bowel loops, penetrates the chest cavity between the sternum and costal parts of the diaphragm.
Diaphragmatic hernia of another type - a hernia of the esophagus passage, arises as a result of congenital shortening of the esophagus. In this case, the upper part of the stomach is located in the chest cavity, and the portion of the stomach, which is localized at the level of penetration through the defect of the diaphragm, is greatly narrowed.