Congenital diaphragmatic hernia

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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.

Bochdalek Hernia
The Bochdalek hernia, also known as a postero-lateral diaphragmatic hernia, is the most common manifestation of CDH, accounting for more than 95% of cases. In this instance the diaphragm abnormality is characterized by a hole in the postero-lateral corner of the diaphragm which allows passage of the abdominal viscera into the chest cavity. The majority of Bochdalek hernias (80-85%) occur on the left side of the diaphragm, a large proportion of the remaining cases occur on the right side, and a small fraction are bilateral i.e., left and right sided defects.

Pathophysiology
It involves three major defects.
 * A failure of the diaphragm to completely close during development.
 * Herniation of the abdominal contents into the chest
 * Pulmonary Hypoplasia

Presentation and Diagnosis
This condition can often be diagnosed before birth and fetal intervention can sometimes help, depending on the severity of the condition. Infants born with diaphragmatic hernia experience respiratory failure due to both pulmonary hypertension and pulmonary hypoplasia. The first condition is a restriction of blood flow through the lungs thought to be caused by defects in the lung. Pulmonary hypoplasia or decreased lung volume is directly related to the abdominal organs presence in the chest cavity which causes the lungs to be severely undersized, especially on the side of the hernia.

Survival rates for infants with this condition vary, but have generally been increasing through advances in neonatal medicine. Work has been done to correlate survival rates to ultrasound measurements of the lung volume as compared to the baby's head circumference. This figure known as the lung to head ratio (LHR) may be used to determine if fetal surgery may be used as an option.

Treatment
ECMO has been used as part of the treatment strategy at some hospitals.

Morgagni's Hernia
This rare anterior defect of the diaphragm is variably referred to as Morgagni’s, retrosternal, or parasternal hernia. Accounting for approximately 2% of all CDH cases, it is characterised by herniation through the foramina of Morgagni which are located immediately adjacent to the xyphoid process of the sternum. The majority of hernias occur on the right side of the body and are generally asymptomatic. However, newborns may present with respiratory distress at birth similar to Bochdalek hernia. Additionally, recurrent chest infections and gastrointestinal symptoms have been reported in those with previously undiagnosed Morgagni's hernia. In asymptomatic individuals laparoscopic surgical repair is still recommended as they are at risk of a strangulated intestine.

Diaphragm Eventration
The diagnosis of congenital diaphragmatic eventration is used when there is abnormal displacement (i.e. elevation) of part or all of an otherwise intact diaphragm into the chest cavity. This rare type of CDH occurs because in the region of eventration the diaphragm is thinner, allowing the abdominal viscera to protrude upwards. This thinning is thought to occur because of incomplete muscularisation of the diaphragm, and can be found unilaterally or bilaterally. Minor forms of diaphragm eventration are asymptomatic, however in severe cases infants will present with respiratory distress similar to Bochdalek hernia. Diaphragm eventration is typically repaired thoracoscopically, by a technique called plication of the diaphragm. Plication basically involves a folding of the eventrated diaphragm which is then sutured in order to “take up the slack” of the excess diaphragm tissue.