Omphalocele

An omphalocele is a congenital abdominal wall defect characterized by herniation of the abdominal viscera through the abdominal wall at the umbilicus. The omphalocele mass is covered by a membrane, not skin. The umbilical cord inserts into the mass and the umbilical vessels drape over the surface of the mass before entering the abdomen.

ICD 10- XVII Q79.2

An omphalocele occurs in 3.4 of 10,000 pregnancies and 1-2 per 10,000 live births.¹

During the fourth to fifth week of embryonic development rapid growth of the intestines and liver occurs, and the abdominal wall is formed. At eight weeks gestational age the abdominal cavity is too small for its contents and the bowel protrudes through the abdomen into the base of the umbilical cord. This herniation is a temporary physiological midgut herniation which is visible on ultrasound from 9-12 weeks gestational age. If this herniation is present after 12 weeks gestational age it is no longer physiological and is classified as an omphalocele. Normally, the liver is never outside the abdominal cavity during development. Therefore, if the liver protrudes into the base of the umbilical cord, the herniation is considered pathological at any gestational age.
The protruding abdominal organs are covered by a two-layered membrane composed of amnion and the peritoneum. The umbilical cord inserts into the membrane, and the cord vessels drape over the mass before entering the abdomen.^{2, 3}

 

The etiology of isolated omphalocele remains unclear. When additional abnormalities are suspected, there is a strong association with chromomal abnormalities, in particular trisomy 18.  

Omphaloceles can be divided into small and giant omphaloceles. A small (or minor) omphalocele can often be closed primarily, which is mostly done within 48 hours after birth. If the postnatal defect size equals or is larger than 5 cm, with liver (partly) protruding⁴, closure is usually delayed in view of the viscero-abdominal disproportion.⁵ Infants with such a ‘giant’ omphalocele are at risk of pulmonary hypoplasia, feeding problems and prolonged hospital stay.^6-9  

In up to 80% of omphalocele cases, additional anomalies, most commonly, Beckwith-Wiedemann syndrome are present. Beckwith-Wiedemann syndrome can be suspected in cases of omphalocele with large fetal size and polyhydramnios. Organomegaly of the liver, kidney and tongue may be identified, commonly in the third trimester. The most common associated structural abnormalities are cardiovascular abnormalities, followed by gastrointestinal and urogenital anomalies.^10-12 

Most cases of omphalocele are sporadic and have a low risk of recurrence among first degree relatives. When an omphalocele is a feature of a genetic condition, the condition determines the pattern of inheritance. The most common genetic syndrome associated with omphalocele is Beckwith-Wiedemann syndrome. This syndrome can occur sporadically with a low recurrence risk, but also familial with an autosomal dominant inheritance pattern. 

In centers with good screening ultrasound protocols, 90% of neonates with omphalocele and most of the additional anomalies are detected by prenatal ultrasound from 11 weeks' gestation onwards.^{1, 13} Small omphaloceles can sometimes elude prenatal detection unless careful attention is paid to the appearance of the umbilical cord insertion site (SLIDE.) In approximately one third of cases prenatally thought to be isolated, additional anomalies are detected after birth.^{11, 14, 15} These additional anomalies may influence postnatal outcome, including type of closure.

Previous studies have shown that ultrasound parameters can predict postnatal outcome in fetuses with an omphalocele.^16-22 The ratio between the omphalocele circumference (OC) and the abdominal circumference (AC), the OC/AC-ratio, can predicts the method of postnatal surgical closure.^{19, 21} The OC/AC-ratio is measured by dividing the omphalocele circumference by the abdominal circumference at the level of the defect with exclusion of edema.¹⁹ An OC/AC-ratio in second trimester of 0.66 or higher may predicts a the need for delayed closure of the defect after birth (unpublished data.)  

In the differential diagnosis of an omphalocele one should consider a body stalk anomaly, Pentalogy of Cantrell, gastroschisis and cloacal malformations. 

When an omphalocele is suspected, a thorough search for associated anomalies and invasive testing to determine chromosomal abnormalities is recommended. The fetal heart should be carefully evaluated. Follow-up scans to check for fetal growth, and amniotic fluid volume, calculation of the OC/AC-ratio as well as liver, kidney and tongue size and are recommended.

Neonates with isolated omphaloceles have a good prognosis and up to a 96% survival rate. Depending on the type and number of associated anomalies, survival rates decrease to 14%.¹¹
Neonates typically have normal mental development. Motor delay at age 2 is seen more often in children with a giant omphalocele compared to those with a small omphalocele.⁶
 

When omphalocele is identified, an advanced anomaly scan should be performed. Chromosome testing with either chorionic villus testing between 11-13 weeks of gestation, or amniocentesis should be offered if available. Genetic consultation can be considered, especially in the presence of associated anomalies or a suspicion of Beckwith-Wiedemann syndrome. Counselling by a pediatric surgeon birth as well as counselling by a fetal medicine specialist can be helpful since the prenatal and postnatal frames of reference regarding an omphalocele differ considerably.⁶ Termination of pregnancy, especially if additional abnormalities or a chromosome abnormality is found, should be discussed in countries where this is an option. Delivery at a center with excellent neonatal and pediatric surgery facilities is advised. A vaginal delivery can be performed in the majority of cases with cesarean delivery reserved for the usual obstetric indications. Postnatal screening for associated anomalies at the discretion of the pediatric team is recommended. 

Surgical repair includes either primary or delayed closure of the abdominal wall defect. The approach chosen depends on the size of the omphalocele and/or presence of pulmonary hypoplasia and/or associated anomalies. 
 

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