A defect in the abdominal wall that is present at birth causes an indirect inguinal hernia.
During the development of the fetus in the womb, the lining of the abdominal cavity forms and extends into the inguinal canal. In males, the spermatic cord and testicles descend out from inside the abdomen and through the abdominal lining to the scrotum through the inguinal canal. Next, the abdominal lining usually closes off the entrance to the inguinal canal a few weeks before or after birth. In females, the ovaries do not descend out from inside the abdomen, and the abdominal lining usually closes a couple of months before birth.1
Sometimes the lining of the abdomen does not close as it should, leaving an opening in the abdominal wall at the upper part of the inguinal canal. Fat or part of the small intestine may slide into the inguinal canal through this opening, causing a hernia. In females, the ovaries may also slide into the inguinal canal and cause a hernia.
Indirect hernias are the most common type of inguinal hernia.2 Indirect inguinal hernias may appear in 2 to 3 percent of male children; however, they are much less common in female children, occurring in less than 1 percent.3