Lung | Congenital diaphragmatic hernia (CDH)
The diaphragm is a thin sheet of muscle separating the chest from the abdomen. When this muscle fails to develop properly, it results in a hole that allows the abdominal organs to move up into the chest and interfere with lung development.
- Congenital diaphragmatic hernia (CDH) refers to a hole in the diaphragm, the muscle that separates the organs in the chest from those in the abdomen.
- As a consequence, fetal abdominal organs can move into the chest cavity and cause overcrowding. The fetal heart is shifted in position and the lungs are compressed and underdeveloped.
- CDH is often diagnosed during a routine anatomical ultrasound at 18-22 weeks’ gestation.
- Fetuses with moderate or severe cases of CDH may be eligible for a fetal surgical procedure, performed in-utero, called “fetoscopic endotracheal occlusion (FETO)”. This procedure is intended to stimulate fetal lung growth and may improve outcomes after the baby is born. FETO is being offered in the OFC as part of an international randomized trial.
The diaphragm is a thin sheet of muscle separating the chest cavity from the abdominal cavity. In congenital diaphragmatic hernia (CDH), part of this muscle sheet is incompletely formed. This results in a hole creating a connection between the chest and the abdomen. The defect is most commonly on the left side (85%).
In CDH, the abdominal organs such as the stomach, bowel and/or liver can migrate through the defect in the diaphragm into the chest where they compete with the lungs and heart for space. As a consequence, the heart is typically shifted to the side opposite to the diaphragmatic defect and the lungs are underdeveloped (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 abdominal organs (stomach, liver, or bowel) in the chest.
The severity of CDH can be predicted before birth using a number of factors. If other structural problems are also present, or if there is an associated genetic abnormality, the outcomes are very poor, with only 15 per cent of babies expected to survive after birth. In isolated CDH, the defect in the diaphragm is the only identified problem affecting the fetus. In such cases, the side of the defect (left or right) and the lung sizes (determined using specific ultrasound measurements and MRI) are critical in determining the severity of the condition. Left-sided lesions are associated with better outcomes than right-sided lesions. In fact, for babies with isolated left-sided CDH delivered in high-volume centres like the OFC, overall survival is approximately 70-80 per cent. Cases where the liver has not herniated into the chest are also associated with better survival after birth.
Fetuses with mild CDH or those with associated abnormalities are not eligible for prenatal therapy. They should, nevertheless, always be delivered in specialized centres with a neonatal intensive care unit (NICU) experienced in treating babies born with CDH, as resuscitation and transport of these newborns may be very challenging. At birth, an endotracheal tube (ETT) connected to a ventilator will be inserted in the baby’s windpipe to help with breathing. A nasogastric (NG) tube will also be inserted into the stomach and an intravenous (IV) line will be placed. The baby will be admitted to the neonatal intensive care unit (NICU).
Once the baby’s breathing has been stabilized, surgery will be performed to repair the defect in the diaphragm. This usually takes place within the first week of life. After surgery, the baby is weaned from the ventilator and oral feeding is started.
Fetuses with moderate or severe CDH are eligible for a prenatal fetal therapy called Fetoscopic Endotracheal Occlusion (FETO). This procedure is typically performed at 28-30 weeks’ gestation for severe pulmonary hypoplasia or 30-32 weeks’ gestation for moderate pulmonary hypoplasia. Using a small camera introduced through the maternal abdominal wall and into the womb, a small balloon is placed in the fetal windpipe (trachea). This intentionally blocks the fetal airways, which prevents fluid from leaving the lungs. 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 NICU. The balloon is typically removed at approximately at 34-35 weeks’ gestation.
The procedure is associated with an increased risk of breaking the water early (preterm premature rupture of the membranes) and pre-term birth. The average gestational age at delivery after FETO is 35 weeks. Once the baby is born, treatment will proceed as described above for mild to moderate CDH.
- Left-sided CDH with ultrasound findings predictive of SEVERE pulmonary hypoplasia (i.e. observed/expected lung-to-head ratio (o/e LHR) <25%). With standard postnatal management, these babies have an estimated chance of survival <30 %, and the majority require oxygen therapy for at least one month after birth,
- For Left-sided CDH: they must be willing to participate in a randomized trial (TOTAL), as treatment is currently only offered as part of the trial.
- Right-sided CDH: can be offered FETO outside the TOTAL trial for ultrasound findings of o/e LHR < 45%
- On 2nd of May, 2019 recruitment for the MODERATE pulmonary hypoplasia TOTAL trial ended after recruiting the planned study population of 196 cases. The outcomes should be available by approximately Spring 2020. Treatment of fetuses with moderate hypoplasia is experimental, and until the results of the study become available, FETO will not be offered to patients carrying a fetus with moderate hypoplasia.
- Associated genetic anomalies or major anatomic anomalies
- Cervix <15mm
- Multifetal pregnancy
- Bilateral CDHs
FETO is performed between 28-30 weeks’ gestation for severe pulmonary hypoplasia – ideally closer to 28 weeks. Normal microarray results, fetal echocardiogram and fetal MRI are all required prior to surgery. These may be done at the referring centre. Ideally we would like to do the MRIs at Mount Sinai at approximately 26 weeks. After FETO, inpatient hospitalization for approximately 24 hours is required. After discharge from hospital, patients must reside within one hour of Mount Sinai Hospital until reversal of the occlusion, which is typically performed 6 weeks later at around 34-35 weeks’ gestation. Once the occlusion has been reversed, out-of-province patients will be referred back to their local experienced centre for further antenatal care, delivery and neonatal management. Local patients will be followed and delivered at Mount Sinai Hospital.