A hernia is the protrusion of an organ or piece of tissue from its normally contained space. In the abdomen, a hernia usually involves a piece of bowel, or its lining (called omentum), protruding through a weak area in the abdominal wall. The abdominal wall is made up of layers of different muscles and tissues. Weak spots may develop in these layers to allow contents the abdominal cavity to protrude. The most common hernias are in the groin (inguinal hernias) and in the diaphragm (hiatal hernias). Hernias may be present at birth (congenital), or they may develop at any time thereafter (acquired).

Inguinal hernias are the most common of the abdominal hernias. The inguinal canal is the opening that allows the spermatic cord and testicle to descend from within the abdomen where they develop in a fetus into the scrotum. After the testicle descends, the opening is supposed to close tightly but sometimes the muscles that attach to the pelvis leave a weak area. In women, therefore, inguinal hernias are less likely to occur because there is no need for a permanent opening in the inguinal canal.

A femoral hernia may occur through the opening in the floor of the abdomen where the femoral artery and vein pass through to the leg. Because of their wider bone structure, femoral hernias tend to occur more frequently in women. Obturator hernias are the least common hernia of the pelvic floor. These are mostly found in women who have had multiple pregnancies or who have lost significant weight. The hernia occurs through the obturator canal, another connection of the abdominal cavity to the leg, and contains the obturator artery, vein, and nerve


Hernias of the anterior abdominal wall

The abdominal wall is made up of muscles that mirror each other from right and left. These include the rectus abdominus as well as the internal obliques, the external obliques, and the transversalis. Diastasis recti is not a true hernia but rather a weakening of the membrane where the two rectus abdominus muscles from the right and left come together. When epigastric hernias occur in infants, they occur because of a weakness in the midline of the abdominal wall where the two rectus muscles join together between the breastbone and belly button. Sometimes this weakness does not become evident until later in adult life as it becomes a bulge in the upper abdomen. The belly button, or umbilicus, is where the umbilical cord attached the fetus to mother allowing blood circulation to the fetus. Umbilical hernias cause abnormal bulging in the belly button and are very common in newborns and often do not need treatment unless complications occur. Some umbilical hernias enlarge and may require repair. Spigelian hernias occur on the outside edges of the rectus abdominus muscle and are rare. Incisional hernias occur as a complication of abdominal surgery, where the abdominal muscles are cut to allow the surgeon to enter the abdominal cavity to operate. Although the muscle is usually repaired, it becomes a relative area of weakness, potentially allowing abdominal organs to herniate through the incision.