Congenital Diaphragmatic Hernia (CDH)

Congenital Diaphragmatic Hernia (CDH)

Congenital diaphragmatic hernia (CDH) is a sporadic birth defect that occurs in approximately1 in 3,000 pregnancies. The diaphragm is a muscle that separates the abdomen from the chest. The pressure in the abdomen is greater than the pressure in the chest. When the diaphragm does not form or does not form properly, leaving a gap, the pressure in the abdomen pushes the stomach, bowel and other organs into the chest. The abdominal organs occupying the chest compresses the lungs and does not allow them to grow properly. This is called pulmonary hypoplasia, or lack of lung development. In addition, the arteries within the lungs become thickened, increasing the blood pressure within the lungs, a condition called pulmonary hypertension. Approximately 80% of CDH's are on the left side (left-sided), 15% are right-sided and 5% are on both sides (bilateral). At birh, approximately 50% of babies will die either from pulmonary hypoplasia, pulmonary hypertension or both. Babies that survive may have long-term breathing problems, pulmonary hypertension and other complications, such as brain bleeds, gastrointestinal problems (for example, reflux) and others.

Treatment of CDH before birth (antenatal) has been tried in several different ways to try to avoid death or long-term complications after birth. The first attempts were done by repairing the hernia while the baby was still in the womb, using open fetal surgery. Unfortunately, that approach failed, both from significant maternal complications as well as from lack of improved outcomes over expectant management. Researchers discovered that blocking the airway of the fetus would result in accumulation of lung fluid beneath the blockage, which expanded the lungs and resulted in lung development as well. This technique is called tracheal occlusion, or TO. Quintero and collaborators showed that it is possible to enter the airway of the fetus without having to open the abdomen or the uterus and block the fetal airway with a special device. Because the blockage is done from within the airway, it was called "intraluminal", as opposed to blockage from outside the airway (for example, by tying off the airway). If lung development is achieved, the baby undergoes correction of the hernia after birth. Currently, several centers worldwide are offering intraluminal fetal TO for the antenatal treatment of CDH. Most centers are using a detachable balloon and are reporting approximately 50% survival in severe CDH cases (the ones that otherwise theoretically would have died). Our center offers a self-expanding stent, which can be easily removed at the time of birth and meets all of the requirements of the surgery.

How can one predict which fetuses will do well without antenatal treatment and which would not, and therefore would potentially benefit from tracheal occlusion?

If the compression of the fetal lungs is not severe, such that the lung size is preserved, those babies are likely to do well. In order to gauge if the size of the lungs is appropriate, researchers have proposed different ultrasound formulas:

A) Lung-to-head ratio (LHR). The LHR is calculated by dividing the area of the lung at the level of the heart (LA) by the circumference of the head (HC): LHR = LA/HC. The reason researchers proposed dividing the LA by the HC was to use an ultrasound parameter (HC) that would adjust the measurement by how advanced the pregnancy was (gestational age). A value of the LHR of <1.4, later changed to <1.0, was considered low and those babies would be offered antenatal treatment.

B) Observed vs. Expected LHR (o/e LHR). The LHR was subsequently shown not to remain stable throughout pregnancy. That is, even if the lungs were too small, the LHR would increase beyond 1.0 or 1.4 simply by the nature of the mathematical division. To correct for this, some investigators proposed using a ratio between what the observed value of the LHR was vs. What the value of the LHR should be according to the gestational age. This mathematical modification was supposed to eliminate the dependency between assessment of lung size and gestational age. Different cut-offs of the o/e LHR have been used to predict fetuses with small lungs: <25% (severe), <35% or <45% with liver in the chest (moderate). However, Quintero and colleagues have shown that the o/e LHR does not fix the problem of the dependency of the measurement of the lung size and gestational age using the o/e LHR. It is not surprising, therefore, that the prediction of a small lung using the o/e LHR is true only 50% of the time.

C) Quantitative Lung Index (QLI). Quintero and colleagues noted that the LHR is not a true ratio, but rather a function. Indeed, the area of the lung is measured in mm^2,, whereas the head circumference is measured in mm. Therefore, the division of mm^2 by mm results in mm, and not in a number without units of measurement. This mathematical detail explains why neither the LHR nor the o/e LHR are independent of gestational age. Quintero and colleagues thus proposed a new formula derived from over 34 million permutations of lung and head sizes, which does produce a ratio free of units of measurements and independent of gestational age. The index is called the "Quantitative Lung Index", or QLI. The QLI is calculated by dividing the lung area (LA) by the square of the head circumference (HC^2) and multipled by 100. A QLI of 1.0 is at the 50th percentile for lung growth. In fetuses with left-sided CDH, a QLI <0.6 is="" at="" the="" 0="" 1st="" percentile="" and="" presumed="" to="" predict="" a="" small="" lung="" nbsp="" p="">

What is the best antenatal treatment for fetuses with CDH?

Assuming that one can correctly identify which fetuses have a small lung and thus would potentially benefit from antenatal treatment, the next question is which method to occlude the fetal airway should be used. The following table compares the 2 methods currently being used:

Balloon

Self-expanding stent

Percutaneous

+

+

Intraluminal

+

+

Grows with the trachea

-

+

Obstructs for 4 weeks

?

+

Does not obstruct >4 weeks

?

+

Can be allowed to stay more than 4 weeks

-

+

Can be easily removed at birth

-

+

Does not cause tracheomalacia

-

+

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