Gastroschisis

Gastroschisis represents a congenital defect characterized by a defect in the anterior abdominal wall through which the abdominal contents freely protrude. There is no overlying sac and the size of the defect is usually less than 4 cm. The abdominal wall defect is located at the junction of the umbilicus and normal skin, and is almost always to the right of the umbilicus.

Omphalocele is another congenital birth defect, but it involves the umbilical cord itself, and the organs remain enclosed in visceral peritoneum, and the defect is much larger than in gastroschisis.

Causes
High-risk pregnancies such as those complicated by infection, young maternal age, smoking, drug abuse, or anything that contributes to low birth weight can increase the incidence of gastroschisis, which is more frequent in newborns who are small for gestational age. Whether the intrauterine growth retardation can facilitate the apparition of gastroschisis or the abdominal wall defect impairs fetal growth is not clear yet.

A change in paternity (childbearing with different fathers) has been implicated as a risk factor in a recent study, suggesting that the immune system of the mother may play a role in the development of gastroschisis.

Genetics
Gastroschisis as a stand-alone congenital defect is usually inherited in an autosomal recessive manner. It may begin as a sporadic mutation, can be associated with non-genetic congenital disorders, but has also been observed to be autosomal dominant.



Genetic counseling and further genetic testing, such as amniocentesis, may be offered during the pregnancy, as this and other abdominal wall defects are associated with genetic disorders. If there are no additional genetic problems or birth defects, surgery soon after birth can often repair the opening.

Pathophysiology
At least six hypotheses have been proposed:
 * 1) Failure of mesoderm to form in the body wall
 * 2) Rupture of the amnion around the umbilical ring with subsequent herniation of bowel
 * 3) Abnormal involution of the right umbilical vein leading to weakening of the body wall and gut herniation
 * 4) Disruption of the right vitelline (yolk sac) artery with subsequent body wall damage and gut herniation
 * 5) Abnormal folding of the body wall results in a ventral body wall defect through which the gut herniates
 * 6) Failure to incorporate the yolk sac and related vitelline structures into the yolk sac

The first hypothesis does not explain why the mesoderm defect would occur in such a specific small area. The second hypothesis does not explain the low percentage of associated abnormality compared with omphalocele. The third hypothesis was criticized due to no vascular supplement of anterior abdominal wall by umbilical vein. The fourth hypothesis was commonly accepted, but it was later shown that the right vitelline artery (right omphalomesenteric artery) did not supply the anterior abdominal wall in this area. More evidence is needed to support the fifth hypothesis.

Embryology
During the fourth week of development, the lateral body folds move ventrally and fuse in the midline to form the anterior body wall. Incomplete fusion results in a defect that allows abdominal viscera to protrude through the abdominal wall. The bowel typically herniates through the rectus muscle, lying to the right of the umbilicus.

Prognosis
Current advances in surgical techniques and intensive care management for neonates have increased the survival rate to 90%, in adequate settings. The possibility of prenatal diagnosis either through echosonogram or any other method available allows the mother to be referred to an adequate center where a caesarean section or induced natural birth can be performed before term (as natural birth is recommended and just as safe as with a normal baby), preferably within 2 weeks of term, and allow the immediate surgery to be performed on the newborn.

The general procedure for gastroschisis is to simply tuck the protruding organs back into the opening and apply a belly band pressure until the wound heals itself. New advances have been pioneered in repairing the protruding bowel by placing a protective "silo" around the intestine outside the abdomen, then slowly pressuring the herniated intestine into the abdominal cavity. This new procedure allows for the bowel to return to its intended shape and location without further traumatizing the infant's viscera with undue internal pressure. The main cause for lengthy recovery periods in patients is the time taken for the infants' bowel function to return to normal.

The morbidity is closely related to the presence of other malformations and complications of the wound or the intestine. Patients frequently require more than one surgery.

Epidemiology
The malformation is slightly more frequent in males than females. The frequency of gastroschisis is associated with young maternal age, and low number of gestations. This abnormality is seen in ratio of 1:10,000 and is usually detected before birth.

It has been reported that the incidence of gastroschisis has increased in recent years.