The cause of gastroschisis remains unknown but may be due to an embryological aberration of the vitelline vessels resulting in a paramedian defect distinct from the umbilical stalk, usually on the right. The herniated gut is commonly short and malrotated, indicating a more complex aetiology than merely an abdominal defect. The incidence of the condition appears to be increasing and it is more common among younger gravidas. Smoking and drug abuse are other possible factors.
If the anterior abdominal wall is carefully scrutinized, gastroschisis is not usually missed. Bowel herniates through a paramedian defect distinct from the umbilical vessels. Due to exposure to the amniotic fluid and as a consequence of impaired circulation, the bowel may be tortuous, matted and thickened. The bowel can be some distance from the fetus, often around the feet, so the whole amniotic cavity must be scanned. Gastroschisis is associated with elevated maternal serum alpha-fetoprotein levels. In comparison with omphalocele, associated anomalies are uncommon and may only be found in about 5% of cases. A cardiac examination is usually recommended. Karyotypic abnormalities are rare (< 0.5%).
Omphalocele, the other major condition with an anterior abdominal wall defect, involves herniation of abdominal contents into the umbilical stalk; these are usually enclosed within a sac, although rupture of the covering sac may occur. Body stalk abnormalities can give the impression of gastroschisis but the lower half of the body below the umbilicus is distorted. Normal thickening of the umbilical cord is occasionally mistaken for bowel; Doppler studies should settle the issue. Fetus in fetu can have the appearance of torted gastroschisis with apparently normal bowel within the abdomen and dilated bowel outside.
Anterior abdominal wall defect distinct from the umbilical vessels, usually to the right
Bowel, sometimes thickened and dilated (in the third trimester, maximum diameter for small bowel is 8mm and large bowel is 18mm), floating within the amniotic fluid
No sac visible
Rarely bladder, liver or spleen involvement
Reduced amniotic fluid volume may be seen
Fetus may be small for dates
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