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.
