Lung | Congenital diaphragmatic hernia
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 into the chest and interferes primarily with the development of the fetal lungs.
- Congenital diaphragmatic hernia (CDH) refers to a hole in the diaphragm, the muscle that separates the chest cavity from the abdomen.
- As a consequence of this hole, fetal abdominal organs can move into the chest cavity and cause overcrowding. The fetal heart is shifted in position and the lungs are underdeveloped.
- CDH is often diagnosed during a routine anatomical ultrasound at 18-22 weeks’ gestational age.
- Fetuses with severe cases of CDH may be eligible for a fetal surgical procedure, performed in-utero, called fetoscopic endoluminal tracheal occlusion (FETO). This procedure is intended to stimulate fetal lung growth and may improve outcomes after the baby is born.
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, or defect, creating a connection between the chest and the abdomen. The defect is more commonly on the left side of the diaphragm.
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 different factors. If other structural problems are present, along with the CDH, 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. Isolated CDH refers to situations where the defect in the diaphragm is the only identified structural problem affecting the fetus. In these 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 to moderate CDH 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, 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 intravenous line (IV) will be placed. The baby will be admitted to the NICU.
Once the baby’s breathing has been stabilized, the baby will be transferred to SickKids and 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 severe CDH (with an expected survival after birth of less than 20 per cent) are eligible for a prenatal fetal therapy called Fetoscopic Endoluminal Tracheal Occlusion (FETO).
This procedure is typically performed at approximately 28 weeks’ gestation. 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 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.
Referral Information (for physicians)
- Moderate or severe pulmonary hypoplasia (i.e. observed/expected lung-to-head ratio <35% when liver is ‘down’, or <45% when liver is ‘up’ for left-sided lesions. O/E LHR <45% for right-sided lesions).
- For left-sided lesions: willing to participate in randomized trial.
- Associated genetic anomalies or major anatomic anomalies.
- Cervix <15mm.
- Multifetal pregnancy.
FETO is performed between 28 and 30 weeks’ gestation for severe pulmonary hypoplasia or between 30-32 weeks’ gestation for moderate pulmonary hypoplasia. Normal microarray results, fetal echocardiogram and fetal MRI are all required prior to surgery. These may be organized by the referring centre. 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 around 35 weeks’ gestation. Out-of-province patients will be referred back to their local centre familiar with postnatal diaphragmatic hernia management for further antenatal management and delivery once the occlusion has been reversed. Local patients will be followed and delivered at Mount Sinai Hospital.