Congenital diaphragmatic hernia overview

# Overview
Congenital diaphragmatic hernia (CDH) is a term applied to a variety of congenital birth defects that involve abnormal development of the diaphragm.  The term is used most commonly in reference to Bochdalek hernia, however it can also apply to Morgagni's hernia, diaphragm eventration and central tendon defects of the diaphragm.  A common theme in all scenarios is malformation of the diaphragm; this allows the abdominal contents to protrude into the chest thereby impeding proper lung formation.  Newborns with CDH often have severe respiratory distress which can be life-threatening unless treated appropriately.

# Historical Perspective
CDH was first discovered in 1575, and later received its name in 1848 by Bochdalek, which would end up becoming an alternative name for CDH. Surgical treatment began in 1902 but this was beyond 24 hours after birth. Neonates began to receive surgery within 24 hours of life in 1946. Mortality rates were high due to reduced diagnosis. Multiple studies continue to be conducted in hopes of further understanding the disease, identifying it early and treating it promptly.

# Classification
There are multiple subtypes of Congenital Diaphragmatic Hernia. These include Bochdalek hernia, Morgagni's hernia and Diaphragm Eventration. Of these, the most common subtype is a  Bochdalek hernia in which there is an anatomical defect in the postero-lateral corner of the diaphragm. Morgagni's hernia, which is responsible for approximately 2% of cases, are due to herniation through the foramina of Morgagni.

# Pathophysiology
Congenital diaphragmatic hernia occurs when the development of the diaphragm during the 12th week of gestation is inadequate leading to a discontinuity. Such a defect leads to herniation into the thoracic cavity and resultant  lung hypoplasia. Affected children often experience decreased lung volume, reduced blood circulation through the lungs and resultant respiratory complications.

# Causes
he underlying causes for congenital diaphragmatic hernia are still to be determined, but there have been studies to show a high rate of incidence in occurrence with certain exposures. These include genetic factors and teratogenic exposures such as allopurinol, lithium and mycophenolate mofetil. Genetic Factors can further be sub-divided into aneuploidies, chromosomal anomalies and syndromes. Aneuploidies include Trisomy 13, Trisomy 18, Trisomy 21, and Turner syndrome. Chromosomal anomalies include Pallister-Killian syndrome, Wolf-Hirschhorn syndrome and various other gene deletion syndromes. Associated syndromes include Donnai-Barrow syndrome, LTBP4-related cutis laxa, Cardiac-urogenital syndrome and Tonne-Kalscheuer syndrome.

# Differentiating Congenital diaphragmatic hernia overview from Other Diseases
Congenital diaphragmatic hernia is a condition that often presents in infants, but there are differential diagnosis' to be considered. Some of these include congenital cystic adenomatoid malformation, bronchopulmonary sequestration, bronchogenic cyst, cystic teratoma, neurogenic tumors, and pulmonary agenesis. Hiatal hernia is often seen in adults rather than neonates but should still be differentiated from congenital hernias. Various imaging modalities may be utilized to further differentiate the potential diagnosis'.

# Epidemiology and Demographics
Approximately 4 in every 10,000 live births are affected with  congenital diaphragmatic hernia, with most cases being on the left side and amongst male newborns. due to the development of severe respiratory failure, the mortality rate remains high regardless of the treatment related advancements. In the last two decades, antenatal diagnosis has increased resulting in prompt and more effective treatment.

# Risk Factors
Unlike other hernias that develop to a progressive weakening in the abdominal wall, CDH occurs due to anatomical defects leading to postero-lateral wall weakness. The use of medications and environmental exposures such as allopurinol, lithium and mycophenolate mofetil as well as phenmetrazine, thalidomide, quinine, cadmium and lead can all contribute to the development of CDH. Genetic factors such as trisomy 13, trisomy 18, trisomy 21 and turner syndrome have all been associated with an increased incidence of CDH. A family history such as a parent or sibling affected may contribute to increased risk of CDH development.

# Screening
CDH screening is not done commonly and is often found incidentally. Affected patients can range from being symptomatic to asymptomatic. Second trimester screening can determine cases through the use of ultrasonography and MRI, methods that have been able to detect 60% of right-sided defects and more than 80% of those with left-sided CDH. Patients with polyhydramnios and an extended familial history of CDH dating back three generations should undergo further testing for diagnosis confirmation. Methods to evaluate for CDH include chorionic villus sampling, amniocentesisas well as chromosomal microarray analysis with the help of SNPs.

# Natural History, Complications, and Prognosis
CDH can present as small or large defects, both of which can be detected antenatally and present with varying symptoms depending on the size. Many neonates are initially stable for 24-48 hours, after which they experience acute respiratory distress. Some concerning complications include tracheobronchomalacia, pneumothorax, pulmonary hypertension, pulmonary infections and respiratory failure. Children often experience reduced exercise tolerance, stunted growth due to aversion to oral feeding, gastroesophageal reflux and anatomical chest deformities. Prognosis varies and is dependent on multiple factors. These include defect size, degree of pulmonary hypoplasia, development of pulmonary hypertension and other factors like birth weight and gestational age at birth. Due to ongoing advances in neonatal care, survival rate is now greater than 60%-80%.

# History and Symptoms
CDH symptoms are often affected by the degree of pulmonary hyperplasia. Common symptoms include severe breathing difficulty, Tachypnea, Tachycardia, and Cyanosis. Morgagni's Hernia may present with chest infections and gastrointestinal symptoms.

# Physical Examination
Generally, affected neonates present with respiratory distress, but this may be dependent on the size of the defect to some extent. Tachypnea and tachycardia are common findings. The skin often appears cyanotic. Physical exam findings are of a wide variety and present with findings affecting all systems except ENT and hematological. Children born with CDH should be evaluated for structural birth defects such as cardiovascular, CNS, genitourinary, craniofacial, and ocular defects.

# Laboratory Findings
Due to the fact that it is an anatomical defect, CDH is primarily diagnosed using screening modalities. Lab values may be deranged in correlation with underlying genetic defects. Due to the respiratory complications, arterial blood gases may also be abnormal, indicating an underlying respiratory acidosis.

# Chest X Ray
Common findings on chest x-ray include cyst like structures representing loops of bowel filling the left hemithorax, mediastinal shift to the right, and varying degrees of gas in the abdomen.

# CT
CT findings include diaphragm discontinuity and herniation of large and small bowel as well as intrabdominal solid organs. In cases of Morgagnis Hernia, the liver, mesenteric fat and the bowel can be seen herniating through.

# MRI
Fetal MRI is a useful diagnostic tool that is commonly used in the second and third trimester. It's ability to measure total lung volume and assess herniated liver mass has particularly proven to be helpful. Lungs appear hyperintense whereas the heart, liver, and mediastinum appear hypointense.

# Ultrasound
Ultrasonography findings in cases of CDH include polyhydramnios, an absent or intrathoracic stomach bubble,  mediastinal shift towards the normal side and herniationinto the chest. Ultrasound findings can also help detect the observed-to-expected lung-to-head ratio, which can assist in predicting survival rate.

# Other Imaging Studies
Colour doppler can help identify abnormal positioning of the  umbilical and portal veins that can indicate liver herniation. Findings can help differentiate between left and right sided CDH.

# Other Diagnostic Studies
Diagnostic studied that can be utilized include high resolution ultrasound, chorionic villus sampling, amniocentesis, microarray analysis, and karyotyping. Although these studies are not necessarily diagnostic for CDH, they help identify underlying genetic defects which have a high correlation rate with diaphragmatic hernia's.

# Medical Therapy
Medical therapy can be subdivided according to antenatal and postnatal management. Antenatal management focuses on close monitoring. Fetal therapy may be an option for eligible patients with resultant fetal tracheal occlusion performed at 26-30 weeks to allow increased surfactant formation. Postnatal management primarily focuses on preventing birth before 37 weeks of gestation, as these neonates have been shown to have worse outcomes comparatively. Other postnatal options include the use of ECMO, the use of a nasogastric tube and intubation where required as well as maintaining adequate ventilation and oxygenation. Medications that may be helpful in reducing pulmonary hypertension include inhaled nitric oxide, sildenafil, bosentan, PGE1, and PGI2.

# Surgery
Minimally invasive surgery has become the preferred method of treatment, which can be done thoracoscopically. Such techniques also lead to reduced postoperative pain and potential complications that may be seen with more invasive surgeries.

# Primary Prevention
The goal of Primary prevention is to prevent the occurrence of an illness or a disease before it occurs. Since CDH may be due to genetic abnormalities that develop due to defects early in gestation, they are difficult to detect and prevent until they have developed. In cases where risk factors lead to CDH, avoidance of causative drugs may prove helpful. For drugs that may lead to increased risk of CDH, it is important to provide alternative medications to affected individuals.

# Secondary Prevention
Secondary prevention occurs once the disease has developed and aims to prevent progression and development of further complications. CDH related complications include tracheobronchomalacia, pneumothorax, pulmonary hypertension, pulmonary infections and respiratory failure. Early screening may assist in complication prevention. Genetic counselling should be offered to all affected families as well as the importance of regular follow up.

# Cost-Effectiveness of Therapy
CDH is primarily treated with extensive surgical intervention which can be very expensive. Annual costs increase with the addition of ECMO. The average cost is USD $137,000 per patient and the estimated cost of CDH per year in the United States alone is more than USD $230 million.

# Future or Investigational Therapies
Many advances have been made to detect or treat CDH earlier than before. These include fetal endoscopic tracheal occlusion, ventilation, in depth studies using chromosome microarray analysis and continued genetic counselling.