Inguinal hernias are the most common abdominal hernias (about 90%) and are seen most often in men. (Femoral hernias are more common for women.) They are a caused by a loop of intestine passing through a weak point in the abdomen and forming a bulge visible through the skin.

Inguinal hernias occur above the level of the inguinal ligament, a ligament that runs from the anterior superior iliac spine of the pelvic bone, to the pubic tubercle of the pubic bone. There are two types of inguinal hernia, direct and indirect hernias, and they have slightly different causes. The two types can be defined anatomically by whether they are lateral (indirect) or medial (direct) to the inferior epigastric artery.

Indirect inguinal hernias

An indirect inguinal hernia is ultimately the result of the failure of embryonic closure of the internal inguinal ring after passage through it of the testicle and the trailing supply of blood vessels and nerves which make up the spermatic cord. The internal ring, which is the beginning of the inguinal canal, was initially formed by the processus vaginalis, a fold of peritoneum which breaches the abdominal wall to make way for the descending testicle. An indirect hernia occurs when intra-abdominal contents, commonly including preperitoneal fatty tissues and intestines, traverse the ring to enter the inguinal canal. As time passes, the hernia contents may enlarge, extend the length of the canal, and even exit the canal through the external inguinal ring into the scrotum. During surgical repair, or herniorraphy, a surgeon recognizes the "indirect" hernia by noting that its bulge begins lateral to the inferior epigastric vessels, indicating that it arose at the top of the inguinal canal. Conversely, the "direct" inguinal hernia enters part way down the canal through a weak point in the canal's posterior wall, and its bulge is noted to be medial to these vessels.

Direct inguinal hernias

A direct inguinal hernia protrudes through a weakened area in the back of the inguinal canal, entering the inguinal triangle, an area defined by rectus abdominis muscle, the inguinal ligament and the inferior epigastric artery.