Exomphalos and Gastroschisis

Exomphalos literally translated from the Greek means 'outside the navel'. It is also called an omphalocoele. It is a congenital abnormality in which the contents of the abdomen herniate into the umbilical cord through the umbilical ring. The viscera, which often includes the liver, is covered by a thin membrane consisting of peritoneum and amnion.¹

Gastroschisis means 'stomach cleft'. It is a congenital defect of the abdominal wall, usually to the right of the umbilical cord insertion. Abdominal contents herniate into the amniotic sac, usually just involving the small intestine, but sometimes also the stomach, colon and ovaries. Unlike exomphalos, there is no covering membrane.²

Both conditions are sometimes referred to as ventral hernias.

Exomphalos and gastroschisis are the commonest congenital abnormalities encountered by paediatric surgeons.³

One UK study estimated the incidence of exomphalos at 3 in 10,000 births.⁴ Epidemiological studies over 40 years have found an association with increasing age, and its link with genetic factors is evident from twin studies, and from the high incidence in consecutive children and different generations of the same family.³ One study confirmed a high incidence of chromosomal abnormalities.⁵

Another study found that the total prevalence increased in the UK but the birth prevalence decreased, due to improved antenatal detection and termination of pregnancies with multiple abnormalities.⁶ This study also found that for gastroschisis the total prevalence and birth prevalence has increased, and that fewer pregnancies resulted in termination, presumably because there were fewer babies with multiple abnormalities. The birth prevalence in 1996 was 4.72 per 10,000. The study confirmed that the incidence was highest in younger mothers (11-19 year age group compared to 35-39 years for exomphalos) and that there were fewer pregnancies with foetal chromosomal abnormalities (0.8 per cent compared to 30.6 per cent). The increase in prevalence seen in recent years has been described as a 'pandemic' and raises interesting possibilities about interaction between genes and environment.⁷

Both exomphalos and gastroschisis have been linked to conditions affecting placental insufficiency, including maternal illness and infection, drug dependency and smoking.³

Exomphalos and gastroschisis may both present prenatally as a rise in alpha-fetoprotein in the second trimester⁸ or as an abnormality on ultrasound scan.⁹

Exomphalos results in a 4 -12cm abdominal wall defect which may be central, epigastric or hypogastric.³ A large defect may be associated with under-development of the abdominal and thoracic cavities. Associated congenital defects may be evident (see below). One study found that 74.4% of patients with exomphalos had associated defects, as opposed to 16.6% of patients with gastroschisis.¹⁰

Gastroschisis presents as an opening usually less than 5cm in length, to the right of the umbilical cord.³ There is much less variation in size than there is in exomphalos. Other abnormalities are not usually present.

Exomphalos and gastroschisis need to be differentiated from each other and from other causes of an abdominal wall mass. Exomphalos is more centrally placed than gastroschisis, is covered with a membrane, and is more likely to be associated with other congenital defects. The hernial sac in the two conditions also feels different. An exomphalic sac feels firm, and may contain liver and tightly packed bowel, whereas in gastroschisis the sac contains only free loops of bowel and feels softer.²

Other causes of abdominal wall mass include:¹¹

• Physiological bowel herniation. This occurs at 10-13 weeks' gestation and may be detected on ultrasound scan. It can be differentiated from exomphalos as a scan at 15 weeks will show that it has disappeared. A large defect which contains liver indicates exomphalos at any stage.
• Umbilical hernia. These are frequent in premature infants. An ultrasound scan will help to diagnose them.
• Amniotic band syndrome. This is a common cause of abdominal wall defects. This starts with an accidental break in the inner amniotic membrane which results in the fetus being exposed to fibrous amniotic bands. The appearance may be similar to gastroschisis, but a scan may demonstrate the atypical location of the defect and contiguity with amniotic membranes.
• Extrophy of the urinary bladder. This appears on a scan in female babies as a mass superior to the foetal genitalia. Serial scans subsequently fail to demonstrate the presence of a bladder, and other abnormalities of the urogenital system may be detected.
• Limb-body wall complex. There is a severe and fatal anterior abdominal wall defect lateral to the umbilical cord insertion point. Other congenital defects involving the heart, limbs, brain and spine may also be detected.
• Multiple cavernous haemangiomas. These are most frequently found over the lower body. Other surface masses may be found that cause limb hypertrophy. This is called Klippel-Trenaunay-Weber syndrome.
• Pseudo-omphalocoele. This term is used to describe a structurally normal abdomen which has been changed in shape by external pressure. This has been known to occur as a result of pressure from an ultrasound transducer. It can also occur in oligohydramnios and other causes of compression of the lower thoracic wall.

Laboratory tests

• Maternal serum alphafetoprotein (MSAFP) levels. These are raised in exomphalos and gastroschisis. The levels are higher in gastroschisis than in omphalocoele.³
• Karyotyping. The strong link between exomphalos and chromosome abnormalities makes karyotyping an essential part of the investigation of this condition.¹²

Imaging

• Ultrasonography. This is the mainstay of diagnosis. Differentiation of exomphalos from gastroschisis and other causes of abdominal wall mass can be made from the size and site of the defect and any associated features (see Differential diagnosis, above).¹³
• Magnetic Resonance Imaging. This may be helpful as an adjunct to ultrasonography, particularly in identifying abnormalities in the position of the liver.¹⁴

Procedures

• Amniocentesis is indicated if a raised alphafetoprotein is combined with appearances on ultrasound suggestive of exomphalos.³

Exomphalos. This may be associated with a number of other congenital abnormalities including:

• Thoraco-abdominal pentalogy of Cantrell. In this condition exomphalos is associated with a cleft sternum, anterior diaphragmatic hernia, heart defects (ventricular septal defect and ectopia cordis) and an absent pericardium.¹⁵
• Beckwith-Wiedemann syndrome. This is a congenital overgrowth condition characterised by exomphalos, macroglossia and gigantism.¹⁶
• Cloacal extrophy. This is a low exomphalos combined with bladder or cloacal extrophy. It may also be associated with other caudal anomalies, such as meningomyelocele anal atresia and lower-limb anomalies.¹¹

Exomphalos

• A baby with an intact sac is usually medically stable and may not require much in the way of pre-operative medical care. If the sac is ruptures, the medical treatment should be the same as for gastroschisis.
• Fluid intake should be maintained intravenously and the sac covered with non-adherent gauze.
• Replacement of the contents within the abdominal cavity and surgical closure is usually achieved without much difficulty with small to moderate sized sacs. Large exomphalos containing the liver may be more challenging.
• Closure of a giant omphalocoele containing the liver is always challenging. A temporary artificial holding sac (a silo) may need to be constructed. Recently, sterile adhesive film and polypropylene mesh has been used for this purpose.¹⁹ Closure of a large abdominal wall defect may require an artificial patch. A variety of rigid and non-rigid patches have been used. Non-rigid patches have the advantage of revascularisation from liver blood vessels and hence lower chance of sepsis, but the incidence of subsequent secondary herniation is higher.³ One centre has had good results using natural biomaterials (dura and bovine patches).²⁰ Optimal outcomes are obtained by utilising a multidisciplinary approach in both the antenatal and postnatal period.²¹

Gastroschisis

Scheduled preterm delivery may improve postoperative outcome.²² Some patients can be managed by plastic closure (vigorous stretching of the abdominal wall with gradual decompression of the abdominal contents from a temporary silo into the abdomen).²³ In the majority of patients, however, primary closure of the defect is the main objective. However, this may need to be delayed if the intestines are too inflamed and hence too enlarged to be replaced in the abdominal cavity. Recent advances in surgery have resulted in improved cosmetic appearance.²⁴

The baby may furthermore require medical stabilisation before surgery. Respiratory distress may require gastric decompression, and sometimes endotracheal intubation. Fluid loss must be corrected intravenously. The baby should be placed under a radiant heater to minimise heat loss. A broad spectrum antibiotic should be administered to prevent infection.

Parenteral nutrition should be provided via a central venous line, the baby should be catheterised to measure urine output, and digital examination should be performed to dilate the rectum.
The gastroschisis sac will require temporary protection in a reservoir (silo). Recently a spring-loaded silo has been used to good effect.²⁵

• Exomphalos can act as a metabolic drain affecting nitrogen balance and leading to failure to thrive.
• Poor nutritional status can result from the omphalocoele acting as a metabolic drain.
• Hepatomegaly and cholestasis can result from prolonged parenteral feeding.
• Sepsis is highly likely if nutritional status is poor, and this can be further complicated by respiratory dysfunction due to increased intrathoracic pressure. One study of gastroschisis patients found that Enterobacter spp. and Klebsiella spp. were the main pathogenic bacteria found in the gut. 20% of patients developed wound sepsis.²⁶
• A large exomphalos can require several surgical procedures to correct the defect. A prolonged stay in hospital is common, and may be complicated by respiratory compromise requiring intubation.
• Trauma to the liver can be a late complication if it is sited beneath the area normal protected by the rib cage.
• The main complication of gastroschisis is intestinal atresia which can occur in 10-20% of patients.²⁷ In this condition, the mucosa and submucosa of the intestine forms a web or diaphragm which partly obstructs the lumen.²⁸ Malabsorption syndromes are common sequelae.
• Post-operatively, several weeks of intestinal dysfunction is common, and prolonged parenteral feeding may be required, Too tight closure of the defect can result in compromise of pulmonary function, cardiac output and blood circulation to the kidneys.
• Significant loss of viable bowel can result in short gut syndrome in both exomphalos and gastroschisis.²⁹

Exomphalos

Prognosis depends on the size of the defect, whether any associated chromosomal abnormalities are present, and whether complications such as pulmonary dysfunction or sepsis develop. Despite improvements in nutritional and respiratory support, mortality and morbidity still occurs. The mortality rate of uncomplicated exomphalos is 10%, but rises to 100% in the present of chromosomal abnormalities with severe associated defects.¹¹

In one series of 104 patients, five patients died pre-operatively and nineteen died of post-operative complications.³⁰

Gastroschisis

The pre-operative mortality rate is 17%.¹⁷ Most deaths are the result of sepsis, premature deliver or bowel infarction. The post-operative survival rate is 87-100% although the length of hospital stay is prolonged. Poor prognosis is more likely with bowel-related complications, such as necrosis, atresia, severe dilation or thickening of the bowel, or difficulty in closing the defect.

The presence of other congenital anomalies adds to the morbidity. One study of 24 patients found that one-third experienced growth delay. Neurodevelopment was not delayed.³¹

Pre-pregnancy counselling should include advice about a healthy lifestyle with adequate nutrition and the avoidance of smoking and recreational drugs.

The role of folic acid supplementation, whilst established for the prevention of spina bifida, is less supported for the prevention of ventral hernias, although animal experiments suggest it may play a part.³

Termination of pregnancy may be considered if there is a large exomphalos, especially if there are associated congenital abnormalities.