Congenital diaphragmatic hernia

What is congenital diaphragmatic hernia?¹

Congenital diaphragmatic hernia (CDH) is a congenital defect in the diaphragm that allows herniation of abdominal viscera into the thorax. The resulting abnormal lung development leads to pulmonary hypoplasia and pulmonary hypertension, which are the primary determinants of morbidity and mortality for these patients.

An unintended consequence of advances in neonatal care, which have improved survival from 50% to almost 80% over the past three decades, has been the frequency and severity of morbidity among survivors.

Associated diseases, notably cardiac abnormalities, are frequent.

Types of hernia

There are three basic types of hernia:

• Posterolateral Bochdalek's hernia occurs at around 6 weeks of gestation: a left-sided Bochdalek's hernia occurs in approximately 85% of cases.² 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.³ Other features include:
  

  • 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's hernia through the foramen of Morgagni represents about 3% of diaphragmatic hernias. 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.

How common is congenital diaphragmatic hernia? (Epidemiology)

Congenital diaphragmatic hernia occurs in about 1 in 3300 live births.¹

Right-sided lesions are rare (10-15%) compared with left-sided (85%) as the liver plugs the opening. Right congenital diaphragmatic hernia carries a disproportionately high mortality and morbidity.^{4 5}

Risk factors

• The majority of cases are idiopathic.

• Familial clusters have 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 multifactorial inheritance and recently the 15q24-q26 site has been linked with this condition.⁶

• The risk of recurrence in a future pregnancy is about 2%.

Congenital diaphragmatic hernia symptoms (presentation)

Many cases are now diagnosed prenatally on routine ultrasound scans or scans following the discovery of polyhydramnios in the mother.⁷

This allows for detailed planning of the delivery and immediate aftercare of the neonate. Previously undiagnosed cases still occur and these will usually 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.^{8 9} These are the least severe and prognosis is much better.¹⁰

Differential diagnosis

• Pneumothorax.

• Pleural effusion.

• Aspiration syndromes.

• Persistent newborn pulmonary hypertension.

Investigations¹

Many infants are now diagnosed in utero by ultrasound scan.

CXR 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. Blood electrolytes, calcium and glucose should also be closely monitored.

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.

Chromosomal analysis may be indicated.

The severity of congenital diaphragmatic hernia can be estimated prenatally using observed-to-expected lung–head ratios (by ultrasound) and total fetal lung volumes (by MRI), as well as fetal liver position.

Associated diseases

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 they 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 Pallister-Killian syndrome (tetrasomy 12p mosaicism).

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

Congenital diaphragmatic hernia treatment and management¹

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.

Infants with CDH require intensive cardiopulmonary support after birth, including immediate endotracheal intubation and “gentle" mechanical ventilation, as well as careful fluid and inotropic support. 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 orogastric 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 (eg, inotropic agents and hypertonic solutions).

Pulmonary hypertension, as assessed by echocardiography, may require the use of pulmonary vasodilators and other medical adjuncts (eg, prostaglandin E1, milrinone) or, in severe cases, extracorporeal life support, if available.

Non-surgical management

The aim is to optimise oxygenation while avoiding barotrauma.¹¹ 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 dubious but others report a positive outcome in the management of pulmonary hypertension associated with congenital diaphragmatic hernia.¹²

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.¹³

Surgical management

Open surgical repair of the diaphragmatic defect should usually be delayed until physiologic stability has been achieved.

Surgery consists of replacing the abdominal organs within the abdominal cavity and repairing the diaphragmatic defect.

Many surgeons now prefer to operate when echocardiography has shown normal pulmonary arterial pressures maintained for at least 24 to 48 hours. Therefore, delayed surgical repair is now usual, performed as an elective procedure, and rarely as an out-of-hours procedure.¹¹

• Respiratory support will be required before, during and after surgery and, extracorporeal membrane oxygenation (ECMO) may be used to maintain oxygen levels whilst allowing the lungs to recover. 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. It is used where there is severe but reversible respiratory failure in term (or near-term) infants.¹⁴ The addition of surfactant does not seem to offer any benefit.¹⁵

• Circulatory stability, respiratory mechanics and gas exchange deteriorate after surgical repair.

• Thoracoscopic repair has been found safe and efficacious by the National Institute for Health and Care Excellence (NICE).¹⁶

Infants with CDH should undergo long-term, multidisciplinary surveillance that includes standardised neurodevelopmental testing, especially if they are considered high risk (needing pulmonary support at 30 days, needing a patch repair or requiring extracorporeal life support).

Fetal surgery

It is not possible to perform intrauterine correction of the defect of the diaphragm but an innovative approach of ligation or occlusion of the fetal trachea has been developed. 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 technique 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.¹⁷ Optimal timing during gestation and length of occlusion are still under investigation.

Complications¹⁸

The advent of improved prenatal imaging has already improved the prognosis and advances in fetal surgery will undoubtedly further improve the outlook for these children; however, long-term problems are common.

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).

They 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 hypoxaemia in the first days of life. 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 three years and further assessment before starting school.

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.

Prognosis

Congenital diaphragmatic hernia is a condition with variable morbidity and mortality. Large population-based studies suggest the overall mortality is close to 70% at 1 year.¹⁹

Pulmonary hypoplasia, persistent pulmonary hypertension and surfactant deficiency are largely responsible for the outcome.

Increasing severity of pulmonary hypertension is associated with increasing mortality. Other factors associated with mortality were birth weight, gestational age at birth, inborn status and need for extracorporeal membrane oxygenation.²⁰

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

For those infants diagnosed in utero, the survival rate is as high as 80% with antenatal diagnosis and optimal care.²¹

Antenatal diagnosis means that the condition is expected, resuscitation is anticipated and delivery can be in a place that offers ECMO - all of which 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.¹⁷ Bilateral hernias are usually fatal. Overall survival is about 50% but this varies between units and according to the individual circumstances of the patient.¹⁸