Definition and Pathophysiology

CDH is a birth defect involving incomplete closure of the pleuroperitoneal membrane.
This results in the herniation of abdominal contents into the thoracic cavity.
It occurs during the 4th to 10th weeks of gestation.
Primary pathology involves lung hypoplasia due to mechanical compression.
Key features include arrested airway branching, decreased pulmonary capillaries, and thickened arteriolar smooth muscle.
These changes lead to severe postnatal pulmonary hypertension and persistent pulmonary hypertension of the newborn (PPHN).

Incidence and Classification

Feature	Characteristics
Common Site	Left hemithorax (85% of cases).
Specific Defect	Foramen of Bochdalek (posterolateral) is most common (95%).
Other Sites	Right-sided (10–15%) or bilateral (<2%).
Associated Anomalies	CHD (15%), neural tube defects, renal anomalies, and trisomies (13, 18, 21).
Syndromes	Fryns, Goldenhar, Pierre Robin, and Beckwith-Wiedemann.

Most cases (60%) are detected during routine anomaly scans at 18–20 weeks.
Antenatal clues include polyhydramnios and an absent or small stomach bubble.
Prognostic markers used to predict postnatal survival include:
- Liver Position: Intrathoracic liver herniation in left-sided CDH indicates a poorer prognosis.
- Lung-to-Head Ratio (LHR): The ratio of the contralateral lung area to head circumference.
- O/E LHR: Observed to expected LHR normalized for gestational age; <15% is extreme and >45% is mild.
- Fetal Lung Volume: Measured via MRI; <30% of expected volume predicts poor survival.

Infants with large defects present at birth with severe respiratory distress and cyanosis.
Classic Physical Signs:
- Scaphoid abdomen.
- Decreased or absent breath sounds on the affected side.
- Heart sounds displaced to the contralateral side.
Small or Morgagni hernias may have a late or subtle presentation with mild respiratory or feeding issues.

Emergency Intubation: Required at birth for most cases to secure the airway.
Avoid Bag-and-Mask Ventilation: This is strictly contraindicated as it distends the stomach and further compresses the lungs.
Decompression: A large-bore orogastric tube must be inserted immediately to vent the gastrointestinal tract.

CDH is a medical, not a surgical, emergency; stabilization is the priority.
Ventilation Strategies:
- Focus on avoiding barotrauma.
- Use gentle ventilation with low peak inspiratory pressures (PIP), often <20–25 cm $H_{2}O$.
- Target preductal $SpO_{2}$ between 85% and 95%.
- Allow permissive hypercapnia ($pCO_{2}$ 45–60 mmHg).
PPHN Management: Inhaled nitric oxide (iNO) is the first-choice therapy; sildenafil or milrinone may be used as adjuncts.
ECMO: May be indicated for infants failing maximal conventional therapy.

Surgery should only be undertaken after the infant is hemodynamically stable and pulmonary hypertension is controlled.
Timing: Usually occurs after 24–48 hours of life.
Procedure: Primary closure of the defect with non-absorbable sutures.
Patch/Flap: Large defects may require a Gore-Tex patch or split abdominal wall muscle flap.

Abdominal Compartment Syndrome: Can occur post-operatively when abdominal domain is small, requiring delayed closure.
Long-term Morbidities:
- Gastrointestinal: Gastroesophageal reflux disease (GERD) is the most common reason for readmission.
- Pulmonary: Chronic lung disease and restrictive or obstructive patterns.
- Neurological: Cognitive defects, behavioral problems, and ADHD.
- Sensory: High risk of sensorineural hearing loss.
- Musculoskeletal: Chest wall deformities and scoliosis.