Congenital Diaphragmatic Hernias

Overview

Definition

• Abnormal connection between the abdominal and chest cavities through a diaphragmatic defect 
• Arises due to the pleuroperitoneal folds failing to fuse during embryonic development

Epidemiology

• Incidence: 1 in 10,000 live births
• No association with gender or ethnicity
• Most commonly sporadic with rare familial incidence
• Associated anomalies occur in about 30% of congenital diaphragmatic hernia (CDH) cases and include: 
  • Lesions of the central nervous system (CNS) and cardiovascular systems 
  • Omphalocele
  • Esophageal atresia
• Associated chromosomal syndromes include: 
  • Trisomies 13, 18, and 21 
  • Turner syndrome
• The majority of CDH are Bochdalek hernias (up to 90%). 
• Morgagni hernias account for only 2%–6% of cases.

Embryology

Multiple embryological mechanisms have been proposed:

• Failure of diaphragmatic structure fusion
  • The diaphragm is composed of 4 embryological structures:
    • 2 pleuroperitoneal membranes
    • Septum transversum
    • Muscular ingrowth from the body wall
  • Failure of these structures to fuse during the 4th to 10th weeks of gestation leaves residual openings that can become hernias.
• Premature involution and malrotation of the midgut
  • 6th week of gestation: The midgut grows rapidly, extending outside the embryo.
  • 9th week of gestation: Midgut twists and re-enters the embryo’s abdomen.
  • Premature re-entry or incorrect rotation of the bowel → higher pressure in the abdominal cavity than the chest cavity → failure of the correct formation of the diaphragm 
• Pulmonary hypoplasia
  • Failure of the lungs to develop appropriately → decreased pressure in the chest cavity
  • Causes a pressure differential that pushes on the diaphragm
  • The diaphragm does not fuse appropriately.

Classification

• Bochdalek hernia: 
  • Constitutes 90% of congenital diaphragmatic hernias
  • Defect in the posterolateral portion of the diaphragm
  • More commonly left-sided with some occurring bilaterally
• Morgagni hernia: 
  • Retrosternal resulting from failure of sternal and crural portions to meet
  • More commonly right-sided 
  • The majority of Morgagni hernias are asymptomatic and discovered incidentally on imaging.
• Hiatal hernia: through the esophageal hiatus
• Paraesophageal hernia: area adjacent to esophageal hiatus

Pathophysiology

Pathological effects of CDH are due to lung hypoplasia:

• Lack of space and increased pressure inhibit lung maturation.
• Decreased bronchial and arterial pulmonary branching
  • Reduced surface area for gas exchange
  • Arterial smooth muscle hyperplasia leading to pulmonary hypertension

Clinical Presentation and Diagnosis

Prenatal diagnosis

• Patients may be diagnosed on routine screening prenatal ultrasound at 16–24 weeks’ gestation.
• Prenatal diagnosis allows for:
  • Family counseling
  • Possible fetal interventions
  • Postnatal planning including referral to a specialized center
• Prenatal ultrasound findings include: 
  • Lung-to-head ratio index (a number below 1 signifies severe CDH)
  • Gastric bubble or liver in the thorax
  • Polyhydramnios
  • Chest mass with or without mediastinal shift

Early postnatal presentation

• Respiratory distress is the most common presenting sign.
  • Tachypnea, grunting, cyanosis 
  • Can develop immediately or up to 2 days after birth
• Characteristic exam findings include:
  • General: craniofacial syndromic findings often noted before signs of CDH
  • Chest: 
    • Increased diameter (barrel chest)  and asymmetry
    • Decreased breath sounds ± bowel sounds ± displaced maximal cardiac impulse
  • Abdomen: scaphoid deformity
• Imaging:
  • To be performed to confirm CDH immediately postnatally
  • Chest X-ray shows tip of the nasogastric tube in the chest.
  • Chest computed tomography (CT) scan may be used for further delineation of the defect.

Delayed presentation

• May present after the neonatal period
• Vomiting with mild respiratory symptoms
• Sepsis and shock may occur due to incarceration of the bowel through the defect.
• May be a rare cause of sudden death in infants and toddlers

Management

Prenatal management

• Close monitoring
  • Monthly ultrasounds to assess fetal well-being and amniotic fluid levels
  • Weekly biophysical profiles in the 3rd trimester
• Amniotic fluid reduction
  • Reduced fetal ability to swallow amniotic fluid may lead to polyhydramnios.
  • Amnioreduction may be indicated.
• Fetal surgeries
  • Reserved for fetuses with a CDH with poor prognosis
  • High rate of failure
  • 2 options:
    • Patch closure of the diaphragmatic defect in utero
    • Fetal endoscopic tracheal occlusion (FETO)

Perinatal management

• Choice of timing and location of birth
  • As close to term as possible (> 39 weeks preferred)
  • In a medical center capable of extracorporeal membrane oxygenation (ECMO)
• Post-natal resuscitation:
  • Aggressive respiratory support with endotracheal intubation
  • Avoidance of prolonged mask ventilation due to increase in intestinal air with further respiratory compromise
  • High-frequency oscillatory ventilation (HFOV), a low-pressure ventilation mode, may be indicated to prevent lung injury.
  • ECMO may be used in children who fail to respond to conventional ventilation and/or HFOV.
• Surgery:
  • Bochdalek hernia: surgical repair recommended 48 hours after stabilization
  • Asymptomatic Morgagni hernia: laparoscopic repair recommended due to risk of future strangulation
  • Paraesophageal hernia: Prompt repair is recommended.

Prognosis

• Indicators of poor prognosis include:
  • Associated major anomalies 
  • Presentation in 1st 24 hours of life
  • Severe lung hypoplasia 
  • Herniation to contralateral thorax
  • Need for ECMO
• Long-term morbidity includes: 
  • Obstructive and/or restrictive pulmonary defects
  • Gastroesophageal reflux disease 
  • Delayed growth in the 1st 2 years of life
  • Neurocognitive deficits (especially in those receiving ECMO)

Differential Diagnosis

• Congenital pulmonary airway malformations (CPAM): rare congenital airway malformations, often cystic in nature. These intrapulmonary structures prevent normal lung tissue expansion predisposing it to infections and malignancy. Like CDH, they can present with tachypnea in a neonate.
• Eventration of the diaphragm: failure of the muscle tissue to cover the diaphragm during fetal development. This leaves only a thin fibrous layer which can then become elevated, protruding into the chest cavity. Eventration of the diaphragm can present like CDH but without true communication between the abdominal and chest cavity.
• Oligohydramnios: insufficient amniotic fluid due to low production (renal dysfunction) or chronic loss during pregnancy, leading to hypoplastic lungs. These patients present with tachypnea and cyanosis, as in CDH, but have no detectable masses in their chest cavity.