A hernia occurs when the contents of a body cavity bulge out of the area where they are normally contained. These contents, usually portions of intestine or abdominal fatty tissue, are enclosed in the thin membrane that naturally lines the inside of the cavity. Although the term hernia can be used for bulges in other areas, it most often is used to describe hernias of the lower torso (abdominal-wall hernias).

Hernias by themselves may be asymptomatic (produce no symptoms), but nearly all have a potential risk of having their blood supply cut off (becoming strangulated). If the blood supply is cut off at the hernia opening in the abdominal wall, it becomes a medical and surgical emergency as the tissue needs oxygen which is transported by the blood supply.

Different types of abdominal-wall hernias include the following:

* Inguinal (groin) hernia: Making up 75% of all abdominal-wall hernias and occurring up to 25 times more often in men than women, these hernias are divided into two different types, direct and indirect. Both occur in the groin area where the skin of the thigh joins the torso (the inguinal crease), but they have slightly different origins. Both of these types of hernias can similarly appear as a bulge in the inguinal area. Distinguishing between the direct and indirect hernia, however, is important as a clinical diagnosis.


o Indirect inguinal hernia: An indirect hernia follows the pathway that the testicles made during fetal development, descending from the abdomen into the scrotum. This pathway normally closes before birth but may remain a possible site for a hernia in later life. Sometimes the hernia sac may protrude into the scrotum. An indirect inguinal hernia may occur at any age.


o Direct inguinal hernia: The direct inguinal hernia occurs slightly to the inside of the site of the indirect hernia, in an area where the abdominal wall is naturally slightly thinner. It rarely will protrude into the scrotum. Unlike the indirect hernia, which can occur at any age, the direct hernia tends to occur in the middle-aged and elderly because their abdominal walls weaken as they age.


* Femoral hernia: The femoral canal is the path through which the femoral artery, vein, and nerve leave the abdominal cavity to enter the thigh. Although normally a tight space, sometimes it becomes large enough to allow abdominal contents (usually intestine) to protrude into the canal. A femoral hernia causes a bulge just below the inguinal crease in roughly the mid-thigh area. Usually occurring in women, femoral hernias are particularly at risk of becoming irreducible (not able to be pushed back into place) and strangulated. Not all hernias that are irreducible are strangulated (have their blood supply cut off ), but all hernias that are irreducible need to be evaluated by a health-care provider.


* Umbilical hernia: These common hernias (10%-30%) are often noted at birth as a protrusion at the bellybutton (the umbilicus). This is caused when an opening in the abdominal wall, which normally closes before birth, doesn't close completely. If small (less than half an inch), this type of hernia usually closes gradually by age 2. Larger hernias and those that do not close by themselves usually require surgery at age 2-4 years. Even if the area is closed at birth, umbilical hernias can appear later in life because this spot may remain a weaker place in the abdominal wall. Umbilical hernias can appear later in life or in women who are pregnant or who have given birth (due to the added stress on the area).


* Incisional hernia: Abdominal surgery causes a flaw in the abdominal wall. This flaw can create an area of weakness in which a hernia may develop. This occurs after 2%-10% of all abdominal surgeries, although some people are more at risk. Even after surgical repair, incisional hernias may return.


* Spigelian hernia: This rare hernia occurs along the edge of the rectus abdominus muscle, which is several inches to the side of the middle of the abdomen.


* Obturator hernia: This extremely rare abdominal hernia develops mostly in women. This hernia protrudes from the pelvic cavity through an opening in the pelvic bone (obturator foramen). This will not show any bulge but can act like a bowel obstruction and cause nausea and vomiting. Because of the lack of visible bulging, this hernia is very difficult to diagnose.


* Epigastric hernia: Occurring between the navel and the lower part of the rib cage in the midline of the abdomen, epigastric hernias are composed usually of fatty tissue and rarely contain intestine. Formed in an area of relative weakness of the abdominal wall, these hernias are often painless and unable to be pushed back into the abdomen when first discovered.