Congenital Diaphragmatic Hernia
The diaphragm is a septum that separates the thoracic from the abdominal cavity. A domelike structure, it consists of muscular and tendinous elements having their origin in costal, sternal, and lumbar sources. The sternal portions are two ﬂat bands that arise from the posterior aspect of the body of the sternum. Costal elements arise from the lowest six ribs and interdigitate with the transversus abdominalis muscles. The lumbar portions arise from the lateral and medial lumbar costal arches.
True congenital diaphragmatic hernias (CDHs) resulting from defects in embryogenesis are through (1) the hiatus pleuroperitonealis (foramen of Bochdalek) without an enclosing sac, (2) the dome of the diaphragm, (3) the foramen of Morgagni, or (4) a defect caused by the absence of the left half of the diaphragm. The two more common types of CDHs are those through the foramen of Bochdalek and the foramen of Morgagni. Foramen of Bochdalek hernias constitute approximately 90% of diaphragmatic hernias in infants and young children; the left side is involved in 85% of cases, and 5% are bilateral. In left-sided cases, the stomach, portions of the small and large intestines, the spleen, and the upper pole of the kidney may herniate through the defect into the pleural cavity and ascend freely to the apex of the chest. On the involved side, lung growth is compromised, but there may be hypoplasia on the contralateral side because shifting of the mediastinum toward the uninvolved side causes some compression of that lung as well.
The timing of onset and severity of symptoms depend on the degree of pulmonary hypoplasia. In severe cases, the infant presents immediately after birth with severe respiratory distress and is difﬁcult to resuscitate.
The presumptive diagnosis can be made from the occurrence of cyanosis and dyspnea soon after birth in infants in whom the cardiac impulse is abnormally sited. In addition, peristaltic sounds may be heard in the thorax, and at the same time, the abdomen is found to be soft and scaphoid in contour. Nowadays, most infants with CDH will have been diagnosed antenatally by routine ultrasonography in the second or third trimester. Postnatally, a standard chest radiograph will show a shift of the mediastinum and a space-occupying lesion on the affected side (e.g., bowel loops occupying the left hemithorax). The differential diagnosis includes other causes of neonatal respiratory distress such as eventration of the diaphragm, cystic adenomatoid mal- formation of the lung, mediastinal cystic teratomas, and loculated hydropneumothorax. Hernias that occur on the right side may be confused with segmental collapse or pleural effusion. However, the posterior location of the mass in the lateral projection and the shift of the heart are helpful ﬁndings. The diagnosis can be conﬁrmed by ultrasonography, the position of the nasogastric tube, or a barium meal.
Infants who require resuscitation in the labor suite should be intubated; bag and mask resuscitation must be avoided to prevent gaseous distension of the herniated bowel and further respiratory embarrassment. A nasogastric tube attached to low suction should be inserted. Infants with CDH are at increased risk of pneumothorax, and this can affect either lung because they are both hypoplastic. It was previously assumed that infants with CDH required immediate postoperative repair in the hope that removal of the bowel from the thorax and closure of the diaphragmatic defect would lead to improvement in gas exchange through expansion of the lung. Studies have demonstrated that a period of perioperative stabilization reduces mortality and the need for extracorporeal membrane oxygenation. The survival of infants with CDH is approximately 60%, with mortality being caused by pulmonary hypoplasia, pulmonary hypertension, or both. Infants who had a CDH may experience problems at follow-up and reherniation, gastroesophageal reﬂux, lung function abnormalities, and exercise intolerance even as adolescents. Attempts to repair the hernia in utero have not been promising. Further antenatal interventions have been based on the discovery that obstructing the normal egress of fetal lung ﬂuid enlarges the lungs, reduces the herniated viscera, and accelerates lung growth in experimental models. Temporary occlusion of the trachea has been achieved by external clips and more recently by internal balloon plugs. Appropriately designed randomized trials are required to determine whether such interventions improve long-term outcome.
Congenital defects in the anterior parasternal region (Laney space) may result in the formation of a foramen of Morgagni hernia. These hernias are usually right sided, and most commonly involve the liver and omentum. The hernia must be differentiated from a pericardial cyst. They may be seen as the part of the pentalogy of Cantrell. Anterior hernias are usually asymptomatic in the neonatal period, but when diagnosed coincidentally on a chest radiograph, they should be repaired because strangulation of the abdominal organs may occur.