A diaphragmatic hernia is defined by an abnormal opening or defect in the diaphragm, the sheet of muscle that separates the chest and abdominal cavities. This structural breach allows abdominal organs to move into the chest. The resulting compression of the heart and lungs makes the condition a serious medical event requiring prompt attention.
What is a Diaphragmatic Hernia?
The diaphragm is a large, dome-shaped muscle that forms a physical barrier between the thoracic cavity (housing the lungs and heart) and the abdominal cavity (containing organs like the stomach, intestines, and liver). As the primary muscle of respiration, the diaphragm contracts and flattens to create negative pressure, pulling air into the lungs. This muscular sheet maintains two separate pressure environments: negative pressure in the chest and relatively positive pressure in the abdomen.
A diaphragmatic hernia occurs when a defect in this barrier allows abdominal contents to push upward into the chest space. Organs such as the stomach, intestine, spleen, or liver can protrude through the opening. The presence of these organs displaces the heart and compresses the lungs, hindering their ability to inflate and function properly. The size and location of the defect determine the severity of the condition.
Causes of Congenital Diaphragmatic Hernia
Congenital diaphragmatic hernia (CDH) results from the diaphragm failing to develop and close completely during fetal development. This developmental error happens early in gestation, typically between the eighth and tenth week of pregnancy. The underlying mechanism is the failure of the pleuroperitoneal folds—the embryological structures that form the diaphragm—to fuse properly.
The etiology of CDH is complex, involving an interplay between genetic and environmental factors. Approximately 30% of babies with CDH have an associated chromosomal abnormality or a single gene defect, indicating a strong genetic component. Researchers have linked mutations in over 150 different genes to CDH, sometimes presenting as a feature of specific genetic syndromes, such as Fryns or Donnai-Barrow syndrome.
Environmental factors can also disrupt diaphragm development. A notable association exists between CDH and deficiencies in maternal vitamin A (retinoic acid) during early pregnancy. Retinoic acid plays an important role in fetal development, suggesting that inadequate levels can impair diaphragm formation. Furthermore, non-diaphragm abnormalities, such as heart or gastrointestinal defects, are present in up to 40% of cases. The most common form of CDH is a posterolateral defect, known as a Bochdalek hernia, which occurs most often on the left side.
Mechanisms Leading to Acquired Diaphragmatic Hernias
Acquired diaphragmatic hernias (ADH) occur after birth, resulting from a physical force that creates a tear or rupture in the diaphragm. The most common cause is severe physical trauma, categorized as blunt or penetrating. Blunt force trauma, such as that sustained in a motor vehicle accident or a significant fall, accounts for the majority of traumatic cases.
The mechanism of injury in blunt trauma involves a sudden rise in intra-abdominal pressure against a closed airway. This abrupt pressure wave can exceed the strength of the diaphragm, causing a large tear that allows abdominal organs to herniate into the chest cavity. Traumatic ruptures occur more frequently on the left side because the liver provides a protective cushion on the right.
Penetrating trauma, such as a stab or gunshot wound to the lower chest or upper abdomen, directly pierces the diaphragm muscle. Even a small opening can become a pathway for abdominal organs to pass into the chest over time, especially due to the pressure gradient. The resulting hernia may be acute, presenting immediately after injury, or delayed by weeks or years.
A third category is iatrogenic hernias, meaning they occur as a complication of a medical procedure. These defects arise from unintentional damage to the diaphragm during chest or abdominal surgeries. Procedures involving the upper abdomen, such as liver resections, may inadvertently weaken or tear the diaphragm, potentially leading to life-threatening complications like organ strangulation.