Congenital Diaphragmatic Hernia (CDH)

Congenital diaphragmatic hernia is a developmental defect in which abdominal viscera pass through an opening in the diaphragm into the thorax. The displaced stomach, bowel, spleen, or liver occupies space needed for lung development. The result is pulmonary hypoplasia: fewer and smaller airways, alveoli, and pulmonary vessels than the infant needs after birth. The underdeveloped pulmonary vascular bed produces high pulmonary vascular resistance. After birth, blood may continue to bypass the lungs through fetal circulatory pathways, causing severe hypoxemia and pulmonary hypertension. Right-ventricular strain, left-ventricular underfilling, and impaired systemic perfusion can follow. Pulmonary hypoplasia and pulmonary hypertension—not simply the size of the diaphragmatic opening—are the major determinants of morbidity and mortality. A large hernia does not always produce the same degree of respiratory failure, and a seemingly stable infant can deteriorate as pulmonary vascular resistance changes during the transition after birth. This is why treatment focuses first on protecting the fragile lungs and supporting circulation rather than immediately closing the defect.