Diaphragmatic hernia usually occurs in the posterolateral portion of the diaphragm (Bochdalek hernia) in 95% of cases and is on the left side in 85% of cases; in 2% of cases it is bilateral. The estimated incidence is 1 to 4 in 10,000 live births. Anterior hernias (Morgagni hernia) are far less common (5% of cases). Other congenital anomalies are present in about 50% of cases, and adrenal insufficiency is relatively common.
Loops of small and large bowel, stomach, liver, and spleen may protrude into the hemithorax on the involved side. If the hernia is large and the amount of herniated abdominal contents is substantial, the lung on the affected side is hypoplastic. Other pulmonary consequences include underdevelopment of the pulmonary vasculature, resulting in an elevation of pulmonary vascular resistance and hence pulmonary hypertension. Persistent pulmonary hypertension leads to right-to-left shunting at the level of the foramen ovale or through a patent ductus arteriosus, which prevents adequate oxygenation even with oxygen supplementation or mechanical ventilation. Persistent pulmonary hypertension is the major cause of death among infants with congenital diaphragmatic hernia.
Respiratory distress typically occurs in the first several hours after birth and occurs immediately after delivery in severe cases. After delivery, as the neonate cries and swallows air, the stomach and the loops of intestine quickly fill with air and rapidly enlarge, causing acute respiratory embarrassment as the heart and mediastinal structures are pushed to the right (with the most frequent left-sided hernia), compressing the more normal right lung. A scaphoid abdomen (due to displacement of abdominal viscera into the chest) is likely. Bowel sounds (and an absence of breath sounds) may be heard over the involved hemithorax.
In less severe cases, mild respiratory difficulty develops a few hours or days later as abdominal contents progressively herniate through a smaller diaphragmatic defect. Rarely, presentation is delayed until later in childhood, sometimes after a bout of infectious enteritis, which causes sudden herniation of bowel into the chest.
Sometimes diaphragmatic hernia is diagnosed by prenatal ultrasonography.
In the delivery room, diaphragmatic hernia may be suspected when newborns with respiratory distress have a scaphoid abdomen.
After delivery, diagnosis is by chest x-ray showing the stomach and intestine protruding into the chest. In a large defect, there are numerous air-filled loops of intestine filling the hemithorax and contralateral displacement of the heart and mediastinal structures. If the x-ray is taken immediately after delivery before the neonate has swallowed air, the abdominal contents appear as an opaque airless mass in the hemithorax.
If diaphragmatic hernia is suspected in a neonate with respiratory distress, the neonate should be immediately endotracheally intubated and ventilated in the delivery room. Bag-and-mask ventilation should be avoided because it may fill the displaced intrathoracic viscera with air and worsen respiratory compromise. Continuous nasogastric suction with a double-lumen nasogastric tube prevents swallowed air from progressing through the gastrointestinal tract and causing further lung compression.
Surgery is required to replace the intestine in the abdomen and to close the diaphragmatic defect after the neonate's lung function, acid-base balance, and blood pressure have been optimally managed.
Severe persistent pulmonary hypertension requires stabilization before surgery with inhaled nitric oxide, which may help dilate the pulmonary arteries and improve systemic oxygenation. Studies show improved outcome with use of extracorporeal membrane oxygenation (ECMO); however, neonates with extreme pulmonary hypoplasia still do not survive. Successful transport of a critically ill neonate with congenital diaphragmatic hernia and persistent pulmonary hypertension is very difficult. Therefore, if diaphragmatic hernia is diagnosed by prenatal ultrasonography, delivery at a pediatric center with ECMO facilities is prudent.