by Lesli A. Taylor, MD

 

The diaphragm is a broad muscle that creates respiration of the lungs by contracting and relaxing. The diaphragm forms at 8 weeks of gestation. This occurs by merging of two membranes to close off the open area between the chest and the abdomen. If it does not close completely, a defect, called a diaphragmatic hernia, is created. The term "hernia" refers both to the hole in the diaphragm muscle and the protrusion of the abdominal organs into the chest.

The most common defect occurs on the left toward the back of the body. This is called a Bochdalek hernia. The hole may be nearly as large as the diaphragm itself. When the diaphragm is completely absent, this is call agenesis of the diaphragm. A less common hernia, called a Morgagni hernia, occurs near the front of the body, near the breastbone.

The stomach, small and large bowel and other organs, such as kidney and liver can herniate up into the chest. Hernias on the left tend to allow many of the abdominal organs into the chest. On the right, the liver covers the hole and there is less chance of bowel or other organs entering the chest.

The biggest problem caused by the herniation of the bowel is that the lung on the affected side and even the lung on the opposite side cannot grow to its fullest capacity. The extent of the lung deficiency becomes apparent at birth when the umbilical card is clamped and infant must oxygenate its blood by breathing.

Diaphragmatic hernia can be diagnosed during pregnancy with ultrasound. This allows the pregnancy to be closely monitored. The mother can be delivered at a specialized center for high risk pregnancies where the pediatric surgeon and ECMO (extra corporeal membrane oxygenation) are available.

Diaphragmatic hernia can be repaired in the womb by fetal surgery, but this is still considered high risk and experimental.

The severity of problems the child will have depends on how big the hole in the diaphragm is, how much of abdominal contents have entered the chest, and at what point in time in gestation the herniation occurred. These factors determine the lung capacity.

Shortly after birth, the baby swallows air while crying and the bowel in the chest inflates with air and further compromises the insufficient lung. Children with severe lung deficiency require intubation and ventilation in the delivery room to survive. Children with better lung capacity may not be detected for several weeks, months or even years, perhaps by a chest x-ray taken for other reasons.

Surgery is required to return the abdominal organs to the abdomen and to repair the diaphragm. There is no surgery at present to repair the lung insufficiency. Lung transplant has been used to replace deficient lungs in diaphragmatic hernia, but this is experimental and obtaining donor lungs for newborns is extremely difficult.

An abdominal chest incision can be used to repair the diaphragm. Many pediatric surgeons prefer to use an abdominal approach as a plastic tent (Silastic silo) can be sewn to the abdominal wall to hold the bowl temporarily in the rare event that the abdominal organs will not fit back in the abdomen. Timing of the repair depends on the patient's stability and the patient's need for ECMO. Bowel injury due to the herniation is rare and is not a reason to operate immediately.

Sometimes the defect is large enough to require synthetic material to close the diaphragm. This will keep the bowel out of the chest, but will not grow with the child. This may lead to detachment of the graft in children with a very large defect. Graft material is a foreign body to the patient and has a greater risk of infection than natural tissues. Muscle flaps have been devised to repair the defect. While there is less risk of infection, the flank will be weak due to loss of two layers of muscle.

Children with severe lung insufficiency can be placed on ECMO if they qualify. This allows circulation of the blood through an external oxygenator pump. Timing of surgery to close the defect in a baby on ECMO is at the discretion of the surgeon.

Recurrence of diaphragmatic hernia is rare. The most important problem the child has after surgery is attaining adequate lung capacity by gradual, though minimal, expansion of the deficient lung, and lung growth with time.