Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia is produced by the failure of the diaphragm to fuse properly during fetal development, allowing the abdominal organs to migrate up into the chest cavity. This results in the two primary problems underpinning congenital diaphragmatic herniae: pulmonary hypertension and pulmonary hypoplasia. This is compounded by dysfunction of the surfactant. Associated diseases, notably cardiac abnormalities, are frequent and outlined below.

There are 3 basic types of hernia:

• Posterolateral Bochdalek hernia occurs at around 6 weeks' gestation: a left-sided Bochdalek hernia occurs in approximately 85% of cases. Left-sided hernias allow herniation of both small and large bowel as well as intra-abdominal solid organs into the thoracic cavity. In right-sided hernias (13% of cases), only the liver and a portion of the large bowel tend to herniate. Bilateral hernias are uncommon and pose very difficult problems.¹ Other features include:²
  • A variable degree of pulmonary hypoplasia with reduction in the area for gas exchange and dysfunction of the surfactant system.
  • Left ventricular hypoplasia is seen in very severe cases.
  • Pulmonary capillary blood flow is decreased because of the small area of the pulmonary vascular bed. It may be further decreased by abnormal pulmonary vasoconstriction.
• Anterior Morgagni hernia through the foramen of Morgani represents about 3% of diaphragmatic herniae. It tends to be small and is easily repaired via the laparoscope.
• Hiatus hernia is often taken as synonymous with gastro-oesophageal reflux disease but the latter is often functional rather than structural in origin. Hiatus hernia only needs repair if symptoms are severe.

Congenital diaphragmatic hernia occurs in 1 in 2000-5000 births and accounts for 8% of all major congenital defects. Males are more commonly affected than females with a ratio of 3:2.

Risk factors

• The majority of cases are idiopathic.
• Familial clusters have been occasionally been observed (<2% of cases) and chromosomal abnormalities are thought to account for approximately 30% of cases. It is thought most likely that these clusters are due to multi-factorial inheritance and recently the 15q24-q26 site has been linked with this condition.³
• The risk of recurrence in a future pregnancy is about 2%.

Most cases are now diagnosed pre-natally on routine ultrasound scans or scans following the discovery of polyhydramnios in the mother. This allows for detailed planning of the delivery and immediate aftercare of the neonate. Previously undiagnosed cases still occur and these will present at - or very soon after - birth depending on the severity of the hernia. Signs include:

• Cyanosis soon after birth
• Tachypnoea
• Tachycardia
• Asymmetry of the chest wall
• Absent breath sounds on one side of the chest, usually the left with the heart shifted to the right.
• Bowel sounds audible over the chest wall
• The abdomen possibly feels " less full" on palpation

About 10% of patients may present rather later than birth, even into adult life. These are the least severe and prognosis is much better.⁴

• Pneumothorax
• Pleural effusion
• Aspiration syndromes
• Persistent newborn pulmonary hypertension

• Many infants are now diagnosed in utero by ultrasound scan.
• Chest x-ray or ultrasound scan will confirm the diagnosis in a neonate who has not previously been diagnosed. Also look for pneumothorax.
• Arterial blood gas measurements are required for pH, PaCO₂ and PaO₂. With persistent pulmonary hypertension with right-to-left ductal shunting, the PaO₂ may be higher from a pre-ductal (right-hand) sampling site.
• Monitor blood for electrolytes, calcium and glucose.
• Ultrasound of the heart and urinary system may be required to assess for other abnormalities.
• Cranial ultrasonography will highlight neural abnormalities such as hydrocephalus and neural tube defects.
• Chromosome analysis may be indicated.

Posterolateral hernia may occur in association with other congenital anomalies and is part of multiple malformations in up to 40% of infants. The other areas involved are principally the cardiovascular, genitourinary and gastrointestinal systems. Retrosternal hernias are also associated with cardiovascular, genitourinary and gastrointestinal malformation. Lethal anomalies are present in up to 16% of infants.

Karyotype abnormalities have been reported in 4% of infants and it may be found in various chromosomal anomalies including trisomy 13 (Patau's syndrome), trisomy 18 (Edwards' syndrome), trisomy 21 (Down's syndrome), Turner syndrome (monosomy X) and Plaister-Killian syndrome (tetrasomy 12p mosaicism).

It may also be associated with nonchromosomal disorders such as the Cornelia de Lange syndrome.

Immediate care

• Children born without a prior diagnosis of congenital diaphragmatic hernia present a paediatric emergency and the initial management must be aimed at reducing the pressure in the chest and increasing oxygenation. If bowel sounds are heard in the chest of a neonate who has respiratory distress, the child should be resuscitated in a "head up", rather than the more usual "head down" position.
• Endotracheal intubation and mechanical ventilation are required for all infants with severe disease who present in the first hours of life.
• Avoid bag-and-mask ventilation in the delivery room because the stomach and intestines become distended with air and further impair lung function.
• Passage of an oro-gastric tube will facilitate location of the stomach on x-ray as well as permitting decompression of the stomach.
• Use of surfactant at an early stage may be beneficial.
• Blood gases should be monitored and an indwelling arterial catheter is advantageous.
• An indwelling venous catheter will enable administration of drugs (e.g. inotropic agents and hypertonic solutions).

Non-surgical management

The aim is to optimise oxygenation while avoiding barotrauma. These infants are critically ill and will invariably need intensive care support. This involves mechanical ventilation, blood pressure support via volume expansion/inotropic agents/colloid agents, monitoring of glucose levels and adequate calcium concentrations. PaO₂ and PaCO₂ targets remain a little controversial. Alkalinisation may be used because of its ability to produce a rapid pulmonary vasodilation. The use of nitric oxide in the management of these children remains controversial. Some have found that the beneficial effects are dubious⁵ but others report a positive outcome in the management of pulmonary hypertension associated with congenital diaphragmatic herniae.⁶ A Cochrane review concluded that it appears reasonable to use inhaled nitric oxide for term and near term infants with hypoxic respiratory failure but only those without a diaphragmatic hernia.⁷

Surgical management

Surgery consists of replacing the abdominal organs within the abdominal cavity and repairing the diaphragmatic defect. It used to be performed early, in the first 24 hours of life. Some suggest that repair 24 hours after stabilisation is ideal but delays of up to 7 or 10 days are often well tolerated. Many surgeons now prefer to operate when echocardiography has shown normal pulmonary artery pressures are maintained for at least 24 to 48 hours. Therefore delayed surgical repair is now usual⁸ and it is performed as an elective and rarely as an out-of-hours procedure.⁹

• Respiratory support will be required before, during and after surgery and in some cases extracorporeal membrane oxygenation (ECMO) may be used to maintain oxygen levels whilst allowing the lungs to recover.¹⁰ This is essentially an adaptation of a coronary bypass involving insertion of catheters into the internal carotid artery, the internal jugular vein (or both) and the use of a membrane lung.² It is used where there is severe but reversible respiratory failure in term (or near-term) infants.¹¹ The addition of surfactant does not seem to offer any benefit.¹²
• Circulatory stability, respiratory mechanics and gas exchange deteriorate after surgical repair.

Fetal surgery

It is not possible to perform intrauterine correction of the defect of the diaphragm but an innovative approach has been developed of ligation or occlusion of the fetal trachea. The fetal lung secretes fluid that provides a template for lung growth. Occlusion of the fetal trachea traps this fluid and stimulates lung growth, either by retention of growth factors within the lung or stimulation of local growth factors by the gentle distension provided by the fluid. In the fetal lamb model, this procedure reverses both pulmonary hypoplasia and vascular abnormalities but does not correct left ventricular hypoplasia.

This has been performed in a small number of cases, using both fetal tracheal occlusion via open hysterotomy and the recently developed video-fetoscopic technique. The results were rather better with the latter technique¹³ but it is still early to decide its place in management. The selection criteria for in utero surgery remain controversial. The position of the fetal liver and the size of the fetal lungs relative to the fetal head are used as indicators of severe disease.¹⁴ Optimal timing during gestation and length of occlusion are still under investigation.

The advent of improved pre-natal imaging has already improved the prognosis and advances in fetal surgery will undoubtedly further improve the outlook for these children but long-term problems are common.¹⁵

Lungs

Some severely affected infants have chronic lung disease (characterised by obstructive and restrictive lung function impairments due to altered lung structure and prolonged ventilatory support)¹⁶ and may require prolonged oxygen and diuretics, as for bronchopulmonary dysplasia. The use of steroids, particularly high doses for prolonged periods, is controversial and may actually hinder appropriate lung and brain development. There are also residual persistent vascular abnormalities which may give rise to recalcitrant pulmonary hypertension.

Nervous system

Nervous system damage may arise as a result of perinatal and neonatal hypoxemia in the first days of life.¹⁶ Possible cerebral injury may be assessed via CT scanning. Before discharge a hearing check should be made and there is a high incidence of hearing loss. This should be repeated at 6 months. Developmental assessment should be made with close follow up for 3 years and further assessment before starting school.²

Feeding

Significant gastro-oesophageal reflux is very common. Most cases can be managed medically but surgical intervention with Nissen or Thal procedures is sometimes required. Failure to thrive may result from increased energy requirements with chronic lung disease, poor oral feeding because of neurological delays and gastro-oesophageal reflux. For those surviving into adulthood, the incidence of oesophagitis is high and Barrett's oesophagus may ensue.¹⁶

Pulmonary hypoplasia, persistent pulmonary hypertension and surfactant deficiency are largely responsible for the outcome. Herniated viscera in the chest per se do not have an adverse effect as long as bowel decompression is continuous using a nasogastric tube.

For those children known to have congenital diaphragmatic hernia but who have not had fetal surgery, prior planning of not only the delivery but also provision of immediate supportive care and emergency surgery has improved prognosis.

For those infants diagnosed in utero, the survival rate is now as high as 80% with antenatal diagnosis and optimal care.¹⁷ Antenatal diagnosis means that the condition is expected, resuscitation is anticipated and delivery can be in a place that offers extracorporeal membrane oxygenation (ECMO) which all improve outcome.

In general those children who do less well are those in whom the fetal stomach is present in the chest and those whose mothers are diagnosed as having polyhydramnios. The presence of associated malformations is also a poor prognostic factor.¹⁴ Bilateral herniae are usually fatal.² Overall survival is about 50%¹⁶ but this varies between units and according to the individual circumstances of the patient.