A congenital diaphragmatic hernia (CDH) occurs when there is abnormal formation of the diaphragm present at birth that creates a connection between the thoracic and abdominal cavities, allowing contents of the abdominal cavity to enter the chest and impairing the normal development and/or function of the lungs and any involved abdominal organs. CDH is a common major congenital abnormality occurring in up to 1:2500 births.

The symptoms can range from asymptomatic to life-threatening severe pulmonary hypoplasia, depending on the size, location, and time at which the herniation occurred during fetal development. The herniated abdominal content may include the liver, stomach, spleen, and bowel. The physical presence of abdominal organs in the chest cavity impairs the normal lung development in the fetus and can result in variable degrees of pulmonary hypoplasia. Pulmonary hypertension results from abnormal pulmonary vascular development. Gastrointestinal (GI) contents in the chest can result in severe refractory gastroesophageal reflux disease (GERD) and intestinal obstruction and GI distress. The infant may present with a scaphoid abdomen resulting from the absence of the herniated GI tract in the abdomen.

CDH is often classified according to the position of its diaphragmatic defect. Bochdalek hernias account for 90% of CDHs and occur on the posterolateral aspect of the diaphragm. Most Bochdalek hernias occur on the right side. Morgagni hernias occur in the front portion of the diaphragm and account for only 2% of all CDHs, with the rest of the hernias occurring in the midsection of the diaphragm.

Approximately 15% of CDHs are syndromic, and up to a quarter of the nonsyndromic cases are associated with other major congenital defects, including congenital defects of the heart, brain, genitourinary system, eyes, and central nervous system (CNS).