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.
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.
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.
FETOSCOPIC ENDOLUMINAL TRACHEAL OCCLUSION (FETO)
‘TOTAL’ (Tracheal Occlusion To Accelerate Lung growth) Trial
- US findings predictive of SEVERE pulmonary hypoplasia:
- o/e LHR (observed/expected lung-to-head ratio) < 25%.
- MRI findings predictive of SEVERE pulmonary hypoplasia:
- o/e TFLV (Total Fetal Lung Volume) < 35%.
- With standard postnatal management, these babies have an estimated chance of survival ≤ 30 %, and the majority require O2 therapy for ≥ 1 month after birth.
- o/e LHR is measured at the latest at 29+5 wks
- FETO is performed between 27+0 – 30+0 wks
- balloon removal is scheduled after 34+0 wks
- US findings predictive of MODERATE pulmonary hypoplasia:
- o/e LHR 25 – 34.9 % (liver position irrelevant) OR
- o/e LHR 35 – 44.9 % with liver in the chest
- With standard postnatal management, estimated chance of survival ~ 50%, and 30% risk of requiring O2 therapy for ≥ 1 month after birth
- o/e LHR is measured at the latest at 32+5 wks
- FETO is performed between 30+0 – 32+0 wks
- balloon removal is scheduled after 34+0 wks
- On 2nd of May, 2019 recruitment for the MODERATE trial ended after completing recruitment of 196 cases.
- On 10th March 2020, recruitment for the SEVERE trial was stopped prematurely by the DSMC (Data Safety & Monitoring Committee) – not for safety concerns.
- The results of both studies have been submitted for publication, and should be available by early Spring 2021. Until the trial results are published, FETO for Moderate or Severe CDH should be discussed with one of the Ontario Fetal Centre team on a case by case basis
- Were not included in the TOTAL trial
- Can be offered FETO for US findings of o/e LHR < 45%
- Associated genetic anomalies or major anatomic anomalies
- Cervix <15mm
- Multifetal pregnancy
- Bilateral CDHs
- 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 wks.
- After FETO, hospitalization for at least 6 hrs may be required.
- After discharge from hospital, patients must reside within 1 hour of Mount Sinai Hospital, until reversal of the occlusion, which is typically performed ~ 6 wks later at ~ 34-35 wks gestation.
- Once the occlusion has been reversed, out-of-province/region patients can return to their local experienced centre for further antenatal care, delivery and neonatal management.
- Local patients will be followed and delivered at Mount Sinai Hospital.