Congenital diaphragmatic hernia (CDH) consists of a developmental defect of the diaphragm with herniation of the abdominal contents in the chest (Figure 138-1). It is a rare condition with an incidence of 1:2000 to 5000 live births with an estimated 1.5:1 male to female ratio. Most cases are isolated but may be associated with other congenital syndromes or chromosomal abnormalities. More than 95% of the defects are due to a defect in the posterolateral diaphragm (at the posterior foramen of Bochdalek) and 80% of these are left sided. Less commonly defects occur in the anterior midline (at the foramen of Morgagni) or in the crural diaphragm (i.e., paraesophageal). Complete diaphragmatic agenesis is rare.
Congenital diaphragmatic hernia. (Reproduced with permission from Doherty GM, ed. Current Diagnosis & Treatment: Surgery. 14th ed. New York, NY: McGraw-Hill Education, Inc.; 2015: Fig. 43-6.)
The defect underlying a CDH is thought to arise from failure of pleuroperitoneal canal closure at 8–10 weeks of gestational age. Herniation of the abdominal contents into the thorax causes compression of the developing lungs which leads to disruption of bronchial and pulmonary arterial branching (i.e., pulmonary hypoplasia). The ipsilateral lung is more severely affected than the contralateral lung. There is evidence in animal models that pulmonary hypoplasia may have a “dual hit” pathogenesis. There may be abnormalities in mesenchymal growth and differentiation of the lung (mesenchymal embryopathy) followed by compression of the lung. Retinoid signaling pathways and decreased airway pressure during fetal life have been implicated as contributing factors in the development of CDH.
The lung shows pulmonary hypoplasia with decreased vascular bed, increased muscularization of small arteries, and increased reactivity of pulmonary vascular bed resulting in increased pulmonary vascular resistances which can possibly lead to right-to-left shunting. There is bilateral lung hypoplasia with decreased bronchial divisions (as few as 6 million from a normal of 20 million) and reduced sacculoalveolar maturation leading to decreased alveolar surface area and decreased alveolar surfactant with abnormal lecithin and sphingomyelin.
The differential diagnosis includes eventration of the diaphragm, pulmonary cystic disease (cystic adenomatoid transformations, pneumatoceles), bronchopulmonary sequestration and cysts, pulmonary agenesis, and pentalogy of Cantrell. CDH is differentiated from these conditions by intrathoracic location of abdominal organs.
Additional associated anomalies occur in 10%–40% of affected fetuses. They may involve the cardiac and outflow defects (ventricular septal defect, tetralogy of Fallot, double outlet ventricle, and transposition of the great arteries) and abnormal great vessels (right or double aortic arch, truncus arteriosus) in one-third of CDH patients. Other defects involve renal, gastrointestinal (malrotation, atresia, omphalocele, tracheoesophageal fistulas), and central nervous system (CNS; spina bifida, anencephaly, and hydrocephalus). These defects are found in 21% of live births and in 95% of still births. Only 5.5% of patients with multiple anomalies survive.