Congenital diaphragmatic hernia

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What is Congenital Diaphragmatic Hernia (CDH)?

The diaphragm is a thin sheet of muscle separating the chest from the abdomen. In congenital diaphragmatic hernia (CDH), part of this muscle sheet is incompletely formed. This results in a hole in the diaphragm, creating a connection between the chest and the abdomen. The hole is most commonly on the left side of the fetus. In CDH, the abdominal organs such as stomach, spleen and liver can migrate through the hole in the diaphragm into the chest where they will compete with the lungs and heart for space. As a consequence, the heart will typically be shifted to the side opposite to the diaphragmatic defect and the lungs will be underdeveloped at birth (pulmonary hypoplasia).

CDH can be diagnosed by ultrasound from the first trimester onward. Typical ultrasound signs are a shifted heart, compressed lungs and the presence of the stomach in the chest.  CDH occurs in about 1-4/10,000 pregnancies. The cause is unknown, although in some cases, it can be part of a genetic disorder.

What is the prognosis (outcome) for a fetus with CDH?

The outcome for fetuses with CDH is dependent on multiple factors. When other severe anatomic or chromosomal problems are present, the outcome is poor, with only 15% of fetuses surviving after birth. In ‘isolated’ CDH, the outcome is dependent on the severity of the pulmonary hypoplasia. The overall neonatal survival of fetuses with isolated left-sided CDH approaches 70-80% in high-volume centers (such as Sick Kids hospital). The prognosis for an individual fetus can be determined using information from ultrasound and MRI. These tools are used to measure the fetal lung size and to assess the fetal liver position. Lung size assessed at ultrasound is typically expressed as the observed compared to the expected lung-to-head ratio (o/e LHR). The larger the o/e LHR, the better the expected outcome for the fetus. In Left sided CDH, an o/e LHR greater than 45% is associated with postnatal survival of over 80%. When the o/e LHR is between 25-45%, postnatal survival is 50-60%. When the o/e LHR is less than 25%, postnatal survival is typically less than 15-20% and this group of fetuses are eligible for inclusion in a trial of FETO. Right sided CDH, fetuses with an o/e LHR less than 45% are candidates for FETO. When the liver is in the chest, outcomes are typically worse than when the liver remains within the abdomen. 

What other tests should we consider?

Any fetus with suspected CDH should be referred to a specialized perinatal center such as the Fetal Medicine Unit at Mount Sinai. A detailed ultrasound should be performed to confirm the diagnosis of CDH, to exclude the presence of associated abnormalities and to assess the size of the lungs and position of the fetal liver. Amniocentesis will often be suggested to determine the fetal karyotype and exclude chromosomal problems. A detailed fetal heart ultrasound (echocardiogram) is often required. A fetal MRI is often suggested to further document the lung size and liver position.

What therapy is available?

Fetuses with mild to moderate CDH are not eligible for prenatal therapy. They should nevertheless always be delivered in tertiary care centers with an intensive care unit experienced in treating CDH, as resuscitation and transport of a neonate with CDH may be very challenging.  A paediatric surgeon (surgeon specializing in newborn surgery) should also be available. At birth, a tube connected to a ventilator will be inserted in the baby’s windpipe to help with breathing. A catheter (NG tube) will also be inserted into the stomach and an IV will be started. The baby will be admitted to the neonatal or paediatric intensive care unit (NICU). Only once the baby’s breathing has been optimized, usually within the first week of life, will surgery be performed to repair the defect in the diaphragm.  After surgery, the baby is weaned from the ventilator and oral feeding is started.

What is the long-term outcome for CDH:

Babies with mild to moderate CDH’s usually have normal long-term outcomes, yet some infants may have delayed mental or motor development. Their lungs also remain fragile and many children need medications similar to those used for asthma. Gastric reflux is common and children may grow more slowly than expected due to feeding problems. Later in life, orthopaedic problems such as scoliosis can occur. Recurrence of the diaphragmatic hernia is relatively rare.

Fetuses with severe CDH (i.e. with an expected postnatal survival less than 20%) are eligible for prenatal therapy (Fetoscopic Endoluminal Tracheal Occlusion – FETO).  In this procedure, at approximately 28 weeks gestation, a small balloon is placed fetoscopically to block the fetal airways, thus preventing the outflow of lung fluid. As the lungs become “inflated” with fluid, lung growth is stimulated. Faster prenatal lung growth leads to bigger lungs at birth and hence better chances of survival and a shorter stay in the neonatal intensive care unit. We try to remove the balloon after approximately 6 weeks. The survival in fetuses who underwent FETO was 50-60%, compared to 15-20% in control fetuses (i.e. without FETO) in a European study of over 200 fetuses. The procedure is nevertheless associated with an increased risk of breaking the water early and pre-term birth. The average gestational age at delivery after FETO is 35 weeks. Postnatal therapy of fetuses which underwent FETO is similar to that described above.

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