"Congenital" means "born with." The diaphragm is the breathing muscle that separates the chest cavity and the abdominal cavity. The diaphragm develops when the fetus is about two months old.
Congenital diaphragmatic hernia (CDH) is the absence of the diaphragm, or a hole in the diaphragm. This can occur on either the left or right side, but is most common on the left.
The contents of the abdomen, including the stomach, intestines, liver and spleen, may go through the hole and into the chest. The contents prevent the normal development of the lung (pulmonary hypoplasia) on that side, and may affect the growth of the other lung. After birth the infant will have difficulty breathing if the lungs are not developed enough.

There are two types of diaphragmatic hernia:
Bochdalek hernia: This type involves an opening on the back side of the diaphragm. The stomach, intestines and liver or spleen usually move up into the chest cavity.
Morgagni hernia: This type is rare and involves an opening in the front of the diaphragm, just behind the breast bone. The liver or intestines may move up into the chest cavity.

As a fetus grows in its mother's uterus before birth, different organ systems are developing and maturing. The diaphragm forms between the 7th and 10th week of pregnancy. The esophagus (the tube that leads from the throat to the stomach), the stomach, and the intestines are also developing at this time.

In a Bochdalek hernia, the diaphragm may not develop properly, or the intestine may become trapped in the chest cavity as the diaphragm is forming. At times, the tendon that should develop in the middle of the diaphragm does not develop properly. In both cases, normal development of the diaphragm and the digestive tract does not occur.
Diaphragmatic hernia is a multifactorial condition, which means that "many factors," both genetic and environmental, are involved. It is thought that multiple genes from both parents, as well as a number of environmental factors that scientists do not yet fully understand, contribute to diaphragmatic hernia.

CDH occurs in about 1 in every 2,500 births. Bochdalek hernias make up about ninety percent of all cases.

FURTHER INFORMATION ON CDH:

DUKE UNIVERSITY MEDICAL CENTER

THE CHILDREN’S HOSPITAL OF PHILADELPHIA

CHILDREN’S MEDICAL CENTER OF DALLAS

TEXAS CHILDREN’S HOSPITAL

REAL HOPE FOR CDH

MASS GENERAL HOSPITAL FOR CHILDREN