Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia is a congenital defect in the diaphragm allowing herniation of abdominal viscera into the thoracic cavity during fetal development, most commonly through the posterolateral Bochdalek defect on the left side.

It produces pulmonary hypoplasia and persistent pulmonary hypertension of the newborn, as a direct consequence of the herniated abdominal contents compressing the developing lung throughout gestation.

It is a life-threatening neonatal surgical emergency with substantial associated mortality. Mortality is predominantly determined by the severity of the pulmonary hypoplasia and pulmonary hypertension rather than by the surgical repair itself. Repair is necessary but is not typically the primary determinant of survival.

Pathophysiology

• Failure of normal diaphragmatic development most commonly affects the posterolateral portion of the diaphragm (the Bochdalek defect). This accounts for the great majority of cases.
• The defect occurs more frequently on the left side, believed to reflect the relative protection afforded to the right hemidiaphragm by earlier hepatic development on that side.
• It allows herniation of abdominal viscera (including bowel, stomach and, in more severe cases, liver) into the thoracic cavity during a critical period of fetal lung development.
• Herniation compresses the developing lung on the affected side. Given the resulting mediastinal shift, it frequently also compresses and impairs development of the contralateral lung.
• The degree and bilaterality of compression directly determine the severity of pulmonary hypoplasia, characterised by reduced numbers of bronchial branches and alveoli together with abnormal, hypertrophied pulmonary vasculature.
• This abnormal pulmonary vascular development underlies the severe persistent pulmonary hypertension of the newborn that develops after delivery.
• The newborn circulation transitions from the fetal pattern, in which pulmonary vascular resistance is normally high and falls rapidly after birth. With abnormal, hypertrophied pulmonary vasculature, this normal fall fails to occur.
• The result is right-to-left shunting across the persistently patent fetal circulatory pathways (foramen ovale and ductus arteriosus) and severe hypoxaemia, the principal, critical determinant of survival in this condition.

• Antenatal ultrasound identifies a substantial proportion of cases, typically showing herniated abdominal viscera within the thoracic cavity together with mediastinal shift.
• This allows antenatal counselling and delivery planning at an appropriate specialist centre with immediate access to neonatal intensive care and paediatric surgical support.
• Where not identified antenatally, affected infants typically present immediately at birth with severe respiratory distress, cyanosis and a scaphoid (concave, sunken) abdomen reflecting displacement of the abdominal contents into the thorax.
• Examination shows reduced or absent breath sounds on the affected side (sometimes with audible bowel sounds within the chest) and displacement of the heart sounds toward the contralateral side, reflecting the mediastinal shift.
• Severity varies considerably according to the degree of pulmonary hypoplasia and the resulting persistent pulmonary hypertension.
• It ranges from severe, immediate and profound respiratory failure at birth (reflecting severe bilateral pulmonary hypoplasia and carrying the poorest prognosis) through to milder presentations with less severe respiratory compromise.
• Uncommonly, presentation is delayed until later in infancy or even childhood, with a smaller defect and correspondingly less severe pulmonary impact.
• Associated congenital anomalies occur in a meaningful proportion of affected infants, including cardiac defects and, in a subset, an underlying genetic syndrome. This underscores the importance of full assessment for associated anomalies as part of the overall evaluation.

• Antenatal ultrasound is the primary diagnostic approach in the substantial proportion of cases identified before birth.
• Fetal magnetic resonance imaging, where available, adds valuable prognostic information including estimation of relative lung volume. This is directly relevant to anticipated severity and guides antenatal counselling and delivery planning.
• Postnatal chest radiography confirms the diagnosis in cases not identified antenatally or presenting acutely at birth. It shows bowel loops or other abdominal viscera within the thoracic cavity together with mediastinal shift and, frequently, a paucity of visible bowel gas within the abdomen given the displaced position of the bowel.
• Full assessment for associated congenital anomalies, including echocardiography and, where clinically indicated, genetic assessment, is an important component of the diagnostic evaluation. This reflects the recognised association and its relevance to prognosis and management planning.
• Ongoing, structured assessment of respiratory status and evidence of persistent pulmonary hypertension is an essential component of postnatal management. It includes echocardiographic assessment of pulmonary artery pressure and the presence and direction of shunting across the foramen ovale and ductus arteriosus, and directly guides the intensity of respiratory and haemodynamic support required.

• Immediate postnatal management prioritises respiratory stabilisation rather than emergency surgical repair. The diaphragmatic defect requires eventual surgical correction but is not the immediate, primary threat to survival.
• Initial management comprises prompt endotracheal intubation, avoiding bag-mask ventilation where possible because of the risk of further bowel distension with air, which worsens the existing thoracic compression.
• Place a nasogastric or orogastric tube to decompress the herniated bowel and stomach. Use gentle, lung-protective ventilation strategies aimed at minimising further lung injury in the setting of pulmonary hypoplasia.
• Management of persistent pulmonary hypertension of the newborn is a central, critical component of ongoing care. It comprises careful, lung-protective mechanical ventilation and inhaled nitric oxide, a selective pulmonary vasodilator and an important, specific treatment for this condition.
• For the most severe cases with inadequate response to conventional management, extracorporeal membrane oxygenation provides temporary cardiopulmonary support to allow time for pulmonary vascular resistance to improve.
• Surgical repair is generally deferred until the infant has achieved a degree of physiological stability, rather than performed as an immediate emergency procedure. Repair does not address the underlying pulmonary hypoplasia and pulmonary hypertension, and premature surgery in a physiologically unstable infant may worsen rather than improve outcome.
• Time surgery individually according to the infant's clinical trajectory and response to initial stabilisation measures.
• Surgical repair comprises reduction of the herniated abdominal viscera back into the abdominal cavity together with closure of the diaphragmatic defect. Use direct primary closure for smaller defects, or a prosthetic patch for larger defects where primary closure would produce excessive tension or is not anatomically feasible.
• Full, ongoing multidisciplinary follow up throughout infancy and childhood addresses the range of long-term morbidities recognised in survivors.
• These include chronic lung disease, gastro-oesophageal reflux (common given the altered anatomical relationships following repair), growth and nutritional difficulty, and neurodevelopmental impairment (reflecting both the direct impact of the condition and the intensity of neonatal intensive care required).
• In a proportion, recurrent diaphragmatic hernia requires further surgical intervention. The long-term, multidisciplinary care needs extend well beyond the immediate neonatal surgical repair.