A diaphragmatic hernia is a medical condition defined by an abnormal opening or defect in the diaphragm, the large, dome-shaped muscle separating the chest cavity from the abdomen. This muscular sheet is essential for respiration, creating the negative pressure necessary for breathing. When a defect exists, abdominal organs (such as the stomach, intestines, liver, or spleen) can push upward into the chest cavity. This movement impairs lung development or function, leading to significant health complications.
The Primary Cause: Failure of Fetal Development
The most common origin of this condition is a failure during fetal development, resulting in a Congenital Diaphragmatic Hernia (CDH). The diaphragm forms from the fusion of several components between the eighth and tenth weeks of gestation. A crucial part of this process involves the closure of the pleuroperitoneal canals by the pleuroperitoneal membranes.
When these membranes fail to fully close, a permanent opening remains, allowing abdominal contents to enter the chest before birth. The presence of these organs prevents the lungs from growing to their normal size, a condition known as pulmonary hypoplasia. This mechanical obstruction and the resulting underdevelopment of the lungs cause the severe respiratory distress often seen in newborns with CDH.
The location of this developmental failure determines the type of congenital hernia. The most frequent form is the Bochdalek hernia, accounting for approximately 70% to 85% of all CDH cases. This defect is located in the posterolateral (back and side) portion of the diaphragm and occurs most often on the left side.
A less common type is the Morgagni hernia, an anterior defect located at the front of the diaphragm, typically accounting for 20% or less of congenital cases. These hernias are found near the sternum and are usually less severe than Bochdalek hernias. The different locations reflect distinct points of failure in the diaphragm’s complex, multi-component fusion process.
Genetic and Chromosomal Risk Factors
While the physical failure of the diaphragm’s fusion is the direct cause of CDH, underlying biological factors contribute to the structural defect. Genetic and chromosomal anomalies are found in approximately 10% to 35% of individuals diagnosed with CDH. This suggests that in a notable portion of cases, the hernia is connected to a broader developmental issue rather than being an isolated event.
The presence of CDH is sometimes linked to specific chromosomal abnormalities, which involve an incorrect number or structure of chromosomes. For instance, CDH occurs more frequently in fetuses with Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome). In these instances, the defect is considered part of a larger syndrome involving multiple organ systems, often referred to as non-isolated CDH.
Beyond large-scale chromosomal changes, rare single-gene mutations are being identified as potential causes. These genes are often involved in complex signaling pathways, such as the retinoid signaling pathway, necessary for normal diaphragm and lung development. Despite these discoveries, the majority of CDH cases are sporadic, meaning they occur without a clear inheritance pattern or known genetic cause.
When CDH is diagnosed, genetic screening is commonly performed to determine if the condition is isolated or associated with a recognized chromosomal or genetic syndrome. This evaluation is important for predicting the overall prognosis and for family counseling, though many isolated cases remain unexplained by current genetic testing.
Acquired Diaphragmatic Hernias
Diaphragmatic hernias can also develop later in life following a significant injury, classified as Acquired Diaphragmatic Hernias (ADH). The most frequent cause of ADH is physical trauma, leading to a Traumatic Diaphragmatic Hernia (TDH). This injury results in a tear or rupture of the diaphragm muscle.
Blunt force trauma, such as motor vehicle collisions or severe falls, is the most common mechanism for TDH. These events cause a sudden, massive spike in intra-abdominal pressure that exceeds the diaphragm’s structural limits, forcing it to tear. The pressure gradient between the high-pressure abdomen and the negative-pressure chest cavity encourages abdominal organs to push through the defect.
Penetrating injuries, including stab or gunshot wounds to the lower chest or upper abdomen, can also directly lacerate the diaphragm, creating an opening. Traumatic hernias occur more frequently on the left side because the liver on the right provides a protective buffer, absorbing some impact and reinforcing the muscle.
In a smaller number of cases, hernias can be iatrogenic, meaning they result unintentionally from a medical procedure. Damage to the diaphragm can occur during certain surgical operations on the chest or abdomen, creating a defect that may not be noticed immediately. Whether from blunt force, penetration, or surgical complication, acquired hernias represent a structural failure caused by an external force rather than a developmental error.