Fetal Ventral Abdominal Wall Defects
Mar 2009 – by R. Tamura, MD
Fetal ventral abdominal wall defects include the more common gastroschisis and omphalocoele and the less common ectopis cordis, limb-body wall complex, cloacal exstrophy and urachal cyst. By the 6th week (8 weeks from the last menstrual period) of development, the abdominal cavity is not large enough to accommodate all its contents and the intestines protrude at the base of the umbilical cord into the residual extraembryonic coelm. This physiologic but transient herniation is evident by ultrasound between the 7th and 9th weeks of development, but resolves by the 10th week of development.
An omphalocele is a midline ventral abdominal wall defect through which the abdominal contents herniate. The defect generally occurs at the base of the umbilicus with the umbilical cord inserting at the apex and is covered by amnion and peritoneum. Large omphaloceles may contain the fetal liver as well as other abdominal organs such as bowel and may be seen by abdominal ultrasound as early as 10 weeks of development (12 weeks from LNMP). Small omphaloceles do not contain the liver, and diagnosis usually occurs after 12 weeks of gestation. Chromosomal abnormalities occur in up to 60% of fetuses with omphaloceles that do not contain the liver. Omphaloceles may be associated with other fetal anomalies and syndromes such as amniotic band syndrome, Pentalogy of Cantrell, Beckwith-Wiedemann syndrome and OEIS syndrome. Up to 50 % of omphaloceles are associated with cardiac defects and gastrointestinal, genitourinary, and central nervous system abnormalities are also present. Fetuses with small omphaloceles are delivered vaginally while for those with defects larger than 5 cm, may be delivered cesarean section. Primary surgical closure is usually performed for smaller omphaloceles; non-surgical options such as silos, elastic bandages and epithelialization with delayed surgical repair are used for larger defects.
Gastroschisis results from a full thickness defect in the ventral abdominal wall. The pathogenesis of gastroschisis is thought to be the result of a vascular accident of either the umbilical vein or the omphalomesenteric artery, and all layers of the abdominal wall are absent. Loops of intestine are seen within the amniotic fluid without overlying amnion or peritoneum. Bowel as well as genitourinary abnormalities are associated with gastroschisis, but there does not appear to be an increase in chromosomal abnormalities. Gastroschisis is associated with some of the highest levels of maternal serum alphaprotein levels as compared to omphaloceles or neural tube defects. Fetuses with gastroschisis are usually delivered vaginally at or near term in a referral center with pediatric surgeons. Immediate repair and closure lessens problems such as infection, hypothermia and acidosis. Primary closure is possible when the bowel can be returned to the abdominal cavity (80% of cases). Otherwise, a silo placement is used to protect the bowel, and surgical repair is performed at a later date.
Ectopia cordis is a defect wherein the heart is partly or completely positioned outside of the thorax and is usually associated withintracardiac defects an pulmonary hypoplasia. Neonatal mortality is high and the diagnosis can be made with ultrasound by the 14th week of gestation.
Pentalogy of Cantrell is caused by the failure of the cephalic body folding. It is characterized by median supraumbilical abdominal wall defect, defect in the sternum, diaphragmatic pericardial deficiency, anterior diaphragmatic deficiency and intracardiac defects. This defect may be diagnosed by ultrasound as early as 11 weeks gestation and has been associated with cystic hygroma, cranial defects and chromosomal abnormalities.
Body stalk anomaly results from the failure of fusion of all four body folds during the 4th week of development and is generally lethal. This anomaly is characterized by cranial defects, facial midline clefts, thoracic and abdominal wall and limb defects. By ultrasound the intrathoracic and abdominal organs may be seen outside of the body cavities within a sac covered by amnioperitoneal membranes and directly attached to the placental with an absent or shortened umbilical cord. The associated scoliosis and omphalocele may appear as an amniotic band syndrome.
Cloacal extrophy results from abnormal caudal folding and may present with hypogastric amphalocele, meningomyelocele, bladder herniation, scoliosis, abnormalities of the renal and genitourinary system. A single umbilical artery is often associated with this defect as are spinal and skeletal defects. Bladder exstrophy also results from abnormal caudal folding but at a lower level of the abdominal wall as compared to cloacal exstrophy and may include defects of the bladder and urethra as well as diastaisi of the symphysis and malposition of the anus. A normal urinary bladder excludes the diagnosis of both types of exstrophy. Surgical correction is undertaken to prevent ascending infection, incontinence and prolapse.
Urachal abnormalities include failure of regression which results in a communication between the anterior abdominal wall and bladder. This may appear as a complete or partially patent urachus, urachal diverticulum, urachal sinus or cyst. A communication between the bladder and cystic mass is confirmatory for a patent urachus. Urachal anomalies are corrected surgically with good outcomes.
- Chromosomal abnormalities are increased with omphaloceles especially those not containing the liver.
- The risk aneuploiy is not increased with gastroschisis.
- Maternal serum alphafetoprotein levels are higher with gastroschisis than with omphaloceles or neural tube defects.
- A membrane surrounding an abdominal defect usually suggests an omphalocele.
- Umbilical cord insertion into the apex of the defect suggests omphalocele. Insertion to the side suggests gastroschisis while below the defect suggests ectopia cordis and above the defect suggests exstrophy.
- Due to physiologic herniation, diagnosis of ventral abdominal defects may not be made before 12 weeks gestation with certainty. Some abdominal wall defect such as body stalk anomaly, ectopia cordis and exstrophy may be made prior to 12 weeks gestation.