| Discussion: |
Gastroschisis is a congenital, full-thickness fusion defect of the anterior abdominal wall that results in herniation of abdominal contents into the amniotic cavity. It typically occurs to the right of the umbilical cord and is not covered by a membrane. Most cases involve the small bowel and portions of the large bowel.
There is controversy regarding the pathophysiology of gastroschisis, but most do agree that it is secondary to a vascular accident. One suggestion is that there is abnormal involution of the right umbilical vein, resulting in weakness of the anterior abdominal wall which subsequently ruptures. Others suggest premature interruption of the right omphalomesenteric artery or rupture of an exomphalos.
A similar congenital defect is an omphalocele. An omphalocele differs from gastroschisis in that it occurs midline at the base of the umbilical cord and is covered by a membrane. It is also associated with other serious structural defects and chromosomal abnormalities, whereas gastroschisis is typically an isolated defect.
Gastroschisis is usually detected during the second trimester ultrasound. It is visualized by bowel protruding through the fetal abdominal wall. Since these free-floating bowel loops lie uncovered in the amniotic fluid, they may become thick and edematous and appear as an echogenic cauliflower-shaped mass.
In addition, it may also be detected by an elevated maternal serum alpha-fetoprotein (AFP) level. Gastroschisis occurs in approximately 1 in 4000 births and is twice as common as an omphalocele.
An omphalocele is also typically detected during the 2nd trimester ultrasound. It is visualized by an anterior midline abdominal mass at insertion of the umbilical cord and there is typically fetal ascites. The mass has a smooth surface and contains bowels, stomach and the liver. There is a membrane covering the viscera, although it may be difficult to visualize. The average size of the defect is 2.5 to 8 cm. Similar to gastroschisis, an omphalocele has an elevated maternal AFP level. In an omphalocele, acetylcholinesterase levels may also be increased.
After diagnosis of gastroschisis in utero, it is recommended to have serial ultrasounds to assess fetal well-being. Many patients are delivered via cesarean section, although this has not been shown to have any benefit over vaginal delivery.
After delivery, it is recommended to cover the bowels with sterile dressings in order to help prevent infection and to preserve fluid and heat.
After delivery the bowel is surgically replaced in the abdomen via primary repair or a staged repair process. In a staged repair, the temporary placement of a silo may be used to help reduce the hernia. The baby usually spends several weeks in the neonatal intensive care unit until the intestines are able to allow feeding.
As mentioned before, gastroschisis is typically an isolated defect. It is, however, associated with other gastrointestinal problems such as intestinal atresia, stenosis and necrosis. These morbidities occur in 25% of patients. Intrauterine growth restriction (IURG) also occurs in most fetuses due to nutrient loss through exposed bowel in the amniotic space. Most mortality in these babies result from necrotizing enterocolitis, and complicated cases unfortunately have short bowel syndrome.
Overall survival is 90% and the babies eventually feed normally and grow up normally.
The prognosis of an omphalocele depends on the severity of the associated co morbidities, such as pulmonary hypoplasia due to the decreased size of the thoracic cavities, or chromosomal defects. When associated anomalies are present, the mortality rate is 80%, but if chromosomal and/or cardiovascular abnormalities are present, it can increase to 100%. If the omphalocele is an isolated defect, it has a similar prognosis to gastroschisis.
Both gastroschisis and omphalocele have increased incidence of adhesions and secondary bowel obstuctions, as a consequence of either the primary repair and often due to their repeated abdominal surgeries.