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3/1/2009

Fetal Ventral Abdominal Wall Defects

Gastroschisis and omphalocele are the most common fetal ventral abdominal wall defects.

Omphalocele is a midline ventral abdominal wall defect through which abdominal contents herniate.  The defect generally occurs at the base of the umbilicus, with the umbilical cord inserting at the apex.  It is covered by amnion and peritoneum.  Large omphaloceles may contain the fetal liver as well as other abdominal organs. Chromosomal abnormalities occur in up to 60% of fetuses with omphaloceles that do not contain liver.  Omphaloceles may be associated with amniotic band syndrome, Pentalogy of Cantrell, Beckwith-Wiedemann syndrome and cloacal exstrophy.  Up to 50 % of omphaloceles are associated with cardiac defects.  Gastrointestinal, genitourinary, and CNS abnormalities can also be present.  Fetuses with small omphaloceles can be delivered vaginally while those with defects larger than 5 cm are typically delivered by cesarean.  Primary surgical closure is usually performed for smaller omphaloceles. 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.  Loops of intestine are seen within the amniotic fluid without overlying membrane.  Bowel and genitourinary abnormalities are associated with gastroschisis.  There does not appear to be an increase in chromosomal abnormalities.  Fetuses with gastroschisis can be delivered vaginally at or near term.  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 is used to protect the bowel, and surgical repair is performed later.

Pentalogy of Cantrell is characterized by a median supraumbilical abdominal wall defect, defect in the sternum, diaphragmatic pericardial deficiency, anterior diaphragmatic deficiency and intracardiac defects.  It has been associated with cystic hygroma, cranial defects and chromosomal abnormalities.

Body stalk anomaly is generally lethal.  It is characterized by cranial, midline facial, thoracic, 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 membranes and directly attached to the placenta with an absent or shortened umbilical cord.  The associated scoliosis and omphalocele may appear as an amniotic band syndrome.

Cloacal exstrophy may present with hypogastric omphalocele, meningomyelocele, bladder herniation, scoliosis, and abnormalities of the renal and genitourinary system.  A single umbilical artery is often associated, as are spinal and skeletal defects.  Bladder exstrophy occurs at a lower level compared to cloacal exstrophy and may include defects of the bladder and urethra as well as diastasis of the symphysis and malposition of the anus.  The diagnosis of both types of exstrophy is excluded by a normal urinary bladder.  Surgical correction is undertaken to prevent ascending infection, incontinence and prolapse.

Urachal abnormalities result in a communication between the anterior abdominal wall and bladder.  They may appear as a complete or partially patent urachus, urachal diverticulum, urachal sinus or cyst.  A communication between the bladder and a cystic mass confirms a patent urachus.  Urachal anomalies are corrected surgically with good outcomes.

Several ultrasound imaging characteristics allow distinguishing between these defects.  Umbilical cord insertion into the apex of the defect suggests omphalocele.  Insertion to the side suggests gastroschisis, while below suggests ectopia cordis and above suggests exstrophy.  Gastroschisis is also associated with higher levels of maternal serum alphaprotein levels than omphaloceles or neural tube defects.  Visualization of an overlying membrane differentiates an omphalocele from other defects.  Due to physiologic herniation, the diagnosis of ventral abdominal defects may not usually be made with certainty before 12 weeks gestation.

Further reading:

O'Connell RV, Dotters-Katz SK, Kuller JA, Strauss RA. Gastroschisis: A Review of Management and Outcomes. Obstet Gynecol Surv. 2016 Sep;71(9):537-44. doi: 10.1097/OGX.0000000000000344.

Prefumo F, Izzi C. Fetal abdominal wall defects. Best Pract Res Clin Obstet Gynaecol. 2014 Apr;28(3):391-402. doi: 10.1016/j.bpobgyn.2013.10.003. Epub 2013 Dec 3.

Initial approval March 2009; Revised February 2015; Reaffirmed November 2017; Reaffirmed May 2019

 

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