A hernia is the abnormal protrusion of an organ or tissue through the wall of the body cavity that normally contains it. This event most frequently occurs within the abdomen, resulting from a weakness or defect in the surrounding muscle or connective tissue layer, known as the fascia. Hernias are classified based on the anatomical location of the defect and the condition of the protruding tissue.
Common Hernias Defined by Location
The most frequently occurring type is the inguinal hernia, accounting for nearly three-quarters of all cases. This type forms in the groin area when tissue, often a portion of the small intestine, pushes through a weakened area in the lower abdominal wall. Inguinal hernias are significantly more common in men due to the natural passage of the spermatic cord through the inguinal canal, which creates an inherent point of weakness.
A femoral hernia also presents as a bulge in the groin, but it occurs lower down, specifically in the upper thigh just below the inguinal crease. These hernias form when tissue protrudes through the femoral canal, a narrow passageway that carries the femoral artery and vein. Unlike inguinal hernias, femoral hernias are much more prevalent in women, which is thought to be related to the wider structure of the female pelvis.
When a protrusion occurs near the navel, it is classified as an umbilical hernia. This type is caused by the failure of the abdominal muscles around the belly button to close completely after birth, leaving a weak spot. While they are common in infants, they can also affect adults, often triggered by conditions that increase abdominal pressure, such as obesity or multiple pregnancies.
Another common type is the hiatal hernia, which involves an internal displacement rather than an external bulge. This occurs when the upper part of the stomach pushes upward through the hiatus, the opening in the diaphragm through which the esophagus passes. Because it affects the function of the lower esophageal sphincter, this type of hernia is often associated with symptoms like heartburn and acid reflux.
An incisional hernia develops at the site of a previous surgical incision in the abdominal wall. The scar tissue formed during healing can create a weak point through which internal tissue can protrude. This type of hernia can manifest months or even years after the initial operation and is often influenced by factors like significant weight gain or excessive strain during the recovery period.
Hernias Classified by Condition
Hernias are also classified based on the condition of the protruding tissue, which indicates the level of medical urgency. The simplest state is a reducible hernia, where the contents can be gently pushed back into the abdominal cavity by manual pressure. This is the least severe form, as the tissue is not trapped and the blood supply remains intact. The bulge may temporarily disappear when the person lies down.
A more concerning state is an irreducible, or incarcerated, hernia, in which the tissue contents become trapped in the defect and cannot be manually returned. Although blood flow to the trapped tissue is still maintained, incarceration presents a high risk of progression to a more serious state. The inability to reduce the hernia is often accompanied by increased pain and visible swelling at the site.
The most serious classification is the strangulated hernia, which represents a medical emergency. This occurs when the neck of the hernia sac constricts so tightly around the protruding tissue that it cuts off the blood supply. Without blood flow, the trapped tissue will quickly begin to die, a process known as necrosis. Strangulation is typically characterized by intense pain, and it can rapidly lead to life-threatening complications such as bowel obstruction and infection.
Specialized and Rare Hernia Types
An epigastric hernia forms in the midline of the abdomen between the navel and the lower part of the breastbone (sternum). This protrusion occurs through a defect in the linea alba, the fibrous structure that runs vertically down the center of the abdominal wall. These hernias usually involve only fatty tissue and are often small in size.
A Spigelian hernia develops along the semilunar line, which is a vertical band of connective tissue running parallel to the edge of the rectus abdominis muscle. This type is unique because it often forms between muscle layers of the abdominal wall, meaning the resulting bulge can be difficult to see or feel during a physical examination. Spigelian hernias are rare, making up less than one percent of all abdominal wall hernias.
Among the rarest types is the obturator hernia, which involves the protrusion of abdominal contents through the obturator foramen in the pelvic bone. This foramen is a small opening covered by the obturator membrane, which allows passage for the obturator nerve and vessels. Due to the complex path it takes through the pelvis, this hernia disproportionately affects elderly, thin women with a wider pelvis.