Omphalocele

Introduction

Omphalocele (also known as exomphalos) is a congenital, abdominal wall defect at the insertion of the umbilical cord. Abdominal contents herniates outside the abdomen within a membranous sac consisting of the peritoneum and amnion (1).

Epidemiology 

Omphalocele is thought to occur in 1 in 5,000 live births (2).

Pathophysiology 

During normal development of the intestines, the midgut begins to elongate at around 6 weeks gestation. However, at this time the liver and stomach are also growing, meaning there is not enough room in the abdomen to accommodate the midgut. In order to continue developing, the midgut herniates through the umbilical ring out of the abdomen into the umbilical cord (called physiological umbilical herniation). During the 10^th week, the abdomen has enlarged enough for the midgut to return (3).

The exact cause of omphalocele is unknown (4), however the main theory is failure of this normal intestinal migration back into the abdominal cavity, and persistence of the physiological umbilical herniation. Other theories include failure of central migration of the two lateral embryonic folds to fuse, or persistence of the body stalk for more than 12 weeks gestation (1, 2).

Risk factors

Risk factors include (2):

• Maternal smoking (possibly due to placental insufficiency and abnormal development of the vascular system).
• Maternal age >40 years old.

Clinical features

Omphaloceles are 4-12 cm abdominal wall defects, located centrally within the umbilical cord (Figure 1). Due to the presence of protective membranes surrounding the herniated gut contents (peritoneum and amnion), the intestines are usually healthy at delivery (2).

Omphalocele has high incidence of associated chromosomal anomalies and syndromes such as:

• Trisomy 13, 18, 21
• Turner syndrome
• Klinefelter syndrome
• Triploidy
• Beckwith-Wiedemann syndrome
• Pentology of Cantrell
• OEIS complex.

By TeachMeSeries Ltd (2024)

Figure 1: An illustration of a newborn with omphalocele.

Differential diagnosis

Gastroschisis – abdominal wall defect usually to the right of the umbilicus involving protruding bowel loops without membranous covering. It has less association with chromosomal anomalies (1).

Cloacal Exstrophy – abdominal wall defect where a segment of large bowel and two halves of the bladder are present outside the abdominal cavity (2).

Physiological gut herniation – herniation of bowel in early pregnancy at 6-8 weeks and subsequent return back into abdominal cavity at 12-13 weeks in utero (1).

Hernia of the cord – where the abdominal wall defect is less than 1.5cm.

By TeachMeSeries Ltd (2024)

Figure 2: Shows the difference between omphalocele and gastroschisis.

Investigations

Omphalocele is a mainly clinical diagnosis (2). It can be diagnosed by prenatal ultrasound or upon birth through physical examination.

Laboratory tests

Alpha-fetoprotein is routinely measured in antenatal screening and is typically elevated in abdominal wall defects. This may be as a result of direct protein loss from the intestine into the surrounding amniotic fluid. Elevated alpha-fetoprotein indicates further assessment through high-definition ultrasound in addition to routine scans (2).

Imaging and Invasive Procedures

Omphalocele can be picked up on routine antenatal ultrasounds in the second trimester (the anomaly scan), when masses outside the abdominal cavity can be detected. If there is evidence of omphalocele, invasive procedures can be performed to assess for associated chromosomal anomalies. This includes chorionic villus sampling at 10-12 weeks or amniocentesis at 15-20 weeks (2).

After birth, a thorough search for associated anomalies should be done along with echocardiography and abdominal ultrasound to check for cardiac and renal anomalies.

Management

Earlier detection through antenatal ultrasound scans is useful for discussion and planning with families about their birth plan. Women should give birth at tertiary care centres for immediate neonatal care if possible (4).

Immediate management

Following delivery, post-natal management includes immediate fluid resuscitation, maintaining adequate temperature and insertion of a nasogastric tube to decompress the bowel. The infant is then transferred urgently to a neonatal intensive care unit (2).

Definitive management 

The surgical principle in omphalocele is reduction of bowel into the abdominal cavity and closure of skin and fascia. The timing of definitive repair will depend on the size of the defect, the baby’s gestational age, and associated anomalies.

In cases with giant omphaloceles with large defects where primary repair is not safe, many surgeons will opt for the use of an agent promote epithelialisation to allow an eschar to develop over the intact amnion sac. This is usually done by silver-impregnated dressings or povidone-iodine solutions. After healing and once the infant is stable, later repair of the abdominal wall hernia is done.

Omphaloceles that have a ruptured membranous sac require immediate surgical intervention, similar to the management of gastroschisis (2).

Complications

• Ruptured omphalocele
• Abdominal Compartmental Syndrome

Prognosis

The prognosis largely depends on the associated congenital anomalies. Giant omphaloceles are generally associated with more long-term medical problems (1).

References