CDH is a condition in which a defect in the diaphragm allows abdominal viscera to herniate into the thorax. The incidence is estimated to be 1 in 2,000 to 5,000 births. Approximately 30% die before birth and 50% of newborns have other anomalies such as cardiac, genitourinary, gastrointestinal, and chromosomal defects. Eighty-five percent of the defects are left-sided, and all CDH infants have some component of pulmonary hypoplasia and pulmonary artery hypertension.

The cause of CDH is not known. The relationship between the developing diaphragm and the lung has been the subject of intense laboratory effort. The big question involves which comes first, the diaphragmatic defect or the lung hypoplasia. It is hypothesized that lung development proceeds normally until 9 to 10 weeks of development, but if the pleuroperitoneal folds fail to close or muscularize at 8 weeks, the intestine is able to pass into the thorax, causing mediastinal shift, compression of thoracic contents, and impairment of subsequent pulmonary growth on both lungs.

CDH has been associated with abnormalities on nearly every chromosome and more commonly with chromosomal duplications or deletions syndromes such as Turner (monosomy), as well as Down, Edward, and Patau (all trisomies). Most cases of CDH, however, occur as isolated nonsyndromic presentations. Associated anomalies are present in a high percentage of fetuses (approaching 40%).

Luckily, CDH is increasingly diagnosed not by neonatal symptoms of respiratory distress, but by prenatal imaging. The findings include polyhydramnios absence of the stomach in the abdomen and presence of abdominal contents in the chest. Newborns with CDH are usually in respiratory distress at the time of delivery. Physical findings include a scaphoid abdomen, displaced heart tones and absent breath sounds on the side of the hernia. Chest and abdominal radiographic findings consist of a bowel gas pattern
in the chest with mediastinal shift. If not diagnosed prenatally, most infants present in the first day of life, but 10% may present later and usually do well because they have sufficient pulmonary function to survive.

In a CDH study group of 2,636 patients, overall survival rate for CDH was 67% but dropped to 41% in those with heart defects. The most common heart defect is ventricular septal defect (42%). Other numerous attempts have been made to correlate prenatal imaging with postnatal outcome, with mixed results. Things such as small lung volume, liver partially or fully intrathoracic, and right-sided heart defects have been found to correlate with poor outcome.

Over the years, CDH management has shifted from a surgical emergency to a physiologic emergency, which necessitates aggressive proactive and efficient management and stabilization of affected newborns. The physiologic emergency arises from the respiratory distress, which is caused by potentially reversible pulmonary hypertension and irreversible pulmonary hypoplasia. Efforts to improve survival have focused primarily on these aspects of hypoplasia and hypertension. Treatments include fetal interventions (tracheal clips), extracorporeal membrane oxygenation (ECMO), surgery, surfactant, nitric oxide, and pulmonary vasodilators (sildenafil). But there remains a paucity of randomized controlled clinical trials in the CDH literature, which makes it difficult to compare differences in therapy, and most of these therapies have not been supported by an evidence based Cochrane review. However, there is a database (the Congenital Diaphragmatic Hernia Study Group) of >2,500 patients providing important information about CDH care and outcome.