INGUINAL HERNIAS: The most common abdominal wall hernias occur in the inguinal canal, an angulated channel that is formed when the muscles on the sides of the lower abdomen (groin area) open up so that the testicles (in males) can migrate outside into the scrotum. This leaves a partially open pathway through which structures that supply the testicle traverse the muscles to reach the testicle. These structures include the testicular artery and veins, the spermatic cord, some fatty tissue, and some nerves and muscle, which are commonly referred to as the “cord”. This leaves a potential weakness in the abdominal wall where inguinal hernias form – either at birth, or early or later in life. In females, there is a corresponding inguinal canal that contains the round ligament, which attaches on the outside to the pubic bone and inside to the uterus, as well as some fat, and nerves and muscle. The inguinal canal is present, but narrower in females – hence inguinal hernias are less common in women. Inguinal hernias can be classified as direct or indirect inguinal(medial or lateral), or femoral hernias, or by type number using the Gilbert Classification.
FEMORAL HERNIAS: Femoral hernias occur in the groin area through an opening between the abdomen and the thigh called the femoral canal. These hernias come out beside the femoral vessels – just medial to the femoral vein. They are more common in women, but can occur in men also. The opening is narrow, so anything that herniates through is more likely to get stuck or trapped outside (incarcerated), and then strangulated.
UMBILICAL HERNIAS: Umbilical hernias occur in the area around the “belly button” or navel. There is a natural opening through which the artery and vein that support the fetus through the umbilical cord and connect to the placenta of the mother during pregnancy come out. This opening usually seals off immediately after birth when the umbilical cord is clamped, but in some babies and children the opening remains and a hernia is present. As we get older, and the abdomen gets larger, particularly in overweight people or in females as a result of pregnancy, the small opening can get larger. This may lead to the development of a hernia defect which allows fat that is normally behind the muscle, to protrude through, creating the bulge or lump. Larger umbilical hernias with wider defects can have intestine coming through the opening as well.
VENTRAL HERNIAS: Ventral hernias are located in other areas of the abdominal wall other than the groin or umbilicus. Typically, they occur in the midline above umbilicus (epigastric hernias), and rarely on the outside of the rectus muscles just below the umbilicus (Spigelian Hernias).
EPIGASTRIC HERNIAS: Most epigastric hernias are in the mid-line between the umbilicus and the xiphoid – the bottom of the sternum. Usually they contain fat, but they can get large and often get incarcerated, especially when the defect is small so the contents get stuck. Larger defects will sometimes allow intestines to come out, making them more dangerous if they get incarcerated and strangulated. Epigastric hernias just above the umbilicus are often found by chance when umbilical hernias are being repaired.
SPIGELIAN HERNIAS: Spigelian hernias occur in the oblique or lateral muscles, often at the outside edge of the rectus muscle where the oblique muscles meet the rectus muscles. They are more common in women. Some Spigelian hernias will not come all the way through all three abdominal wall muscles – they may push the outer muscle (external oblique) outward instead of going through it – this makes it harder to feel the hernia on physical examination, so the diagnosis can be more difficult. Spigelian hernias can contain fat or intestines.
INCISIONAL HERNIAS: Incisional hernias occur in previous abdominal incisions. These can occur anywhere in the abdominal wall. They can be small or can grow to be very large or massive. Patients who have had infections or other complications after previous surgery, or have had multiple procedures, or are overweight, are more likely to develop incisional hernias. Many incisional hernias have more than one defect. Sometimes there are multiple defects which may need to be repaired at the same time. Incisional hernias may have intestine in the contents, which can have adhesions or scarring, and cause intestinal obstruction (blockage), making them more likely to cause problems and need surgery.