Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia is often abbreviated to CDH but this will be avoided here for fear of confusion with congenital dislocation of the hip. An alternative name is congenital diaphragmatic defect and this can be abbreviated to CDD with less ambiguity.

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.

Deficiency of the diaphragm with the presence of abdominal contents in the chest is by no means the only problem. Pulmonary hypoplasia occurs along with pulmonary hypertension and dysfunction of the surfactant system. Cardiac maldevelopment may further complicate the problem.
There are 3 basic types of hernia:

• The posterolateral Bochdalek hernia occurs at around 6 weeks' gestation
• Anterior Morgagni hernia through the foramen of Morgani represents about 3% of diphragmatic herniae.
• Hiatus hernia.

The left-sided Bochdalek hernia occurs in approximately 90% 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, only the liver and a portion of the large bowel tend to herniate. Bilateral hernias are uncommon and pose very difficult problems.¹

There is a variable degree of pulmonary hypoplasia with reduction in the area for gas exchange and dysfunction of the surfactant system. In very severe cases, left ventricular hypoplasia is seen. Pulmonary capillary blood flow is decreased because of the small area of the pulmonary vascular bed, and flow may be further decreased by abnormal pulmonary vasoconstriction.
The anterior Morgani hernia tends to be small and is easliy 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.

The majority of cases are idiopathic, although familial clusters have been observed, and chromosomal abnormalities are thought to account for approximately 15% 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.² The risk of recurrence in a future pregnancy is about 2%.³

10% of patients may present rather later than birth, even into adult life. These are the least severe and prognosis is much better.⁴
Many cases are now diagnosed pre-natally on routine ultrasound scans, or scans following the discovery of polyhydramnios in the mother, and 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.

• 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

• Pneumothorax
• Pleural effusion
• Aspiration syndromes

• Most 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 preductal (right-hand) sampling site.
• Monitor blood for electrolytes, calcium and glucose.
• Ultrasound of the heart and urinary system may be required to assess other abnormalities.
• 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. Lethal anomalies are present in up to 16% of infants.
Karyotype abnormalities have been reported in 4% of infants, and may be found in various chromosomal anomalies including Edwards' syndrome (trisomy 18) and Patau's syndrome (trisomy 13). It may also be associated with nonchromosomal disorders such as the Cornelia de Lange syndrome.
Retrosternal hernias are also associated with cardiovascular, genitourinary, and gastrointestinal malformation.

• 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 the prognosis in this group.
• 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.
• New methods of ventilatory support are improving prognosis.⁵

• Surgery consists of replacing the abdominal organs within the abdominal cavity and repairing the diaphragmatic defect.
• 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.⁶ The addition of surfactant does not seem to offer any benefit.⁷
• In severe cases, nitric oxide has been used but any benefit is dubious.⁸ 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.⁹
• There is doubt about the optimum time to perform surgery. It used to be performed early, in the first 24 hours of life, but it may be that stabilization is more important for prognosis. Pulmonary hypoplasia, persistent pulmonary hypertension and surfactant deficiency are largely responsible for the outcome. Herniated viscera in the chest do not have an adverse effect as long as bowel decompression is continuous using a nasogastric tube.
• Circulatory stability, respiratory mechanics, and gas exchange deteriorate after surgical repair.
• The ideal time for repair is unknown. Some suggest that repair 24 hours after stabilization 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.

Delayed surgical repair is now usual and it is performed as an elective and rarely as an out-of-hours procedure.¹⁰

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 technique¹¹ but it is still rather early to decide its place in management. The selection criteria for in utero surgery remain controversial. Most recently, the position of the fetal liver and the size of the fetal lungs relative to the fetal head are promising as indicators of severe disease. 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.^{12 13}

Lungs

Some severely affected infants have chronic lung disease 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.

Nervous System

Possible cerebral injury may be sought be CT scanning. Before discharge a check for hearing 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.

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.

The prognosis has improved dramatically in the last decade, and for those infants diagnosed in utero, the survival rate is now as high as 80% with antenatal diagnosis and optimal care.¹⁴ 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. Antenatal diagnosis means that the condition is expected, resuscitation is anticipated and delivery can be in a place that offers extracorporeal membrane oxygenation (ECMO). This all improves outcome.¹⁵ Overall survival is about 50% but varies between units and there are features that have a marked influence on outcome.¹³