Indirect inguinal hernia

# Overview
An indirect inguinal hernia a inguinal hernia which results from the failure of embryonic closure of the internal inguinal ring after the testicle has passed through it. Like other inguinal hernias, it protrudes through the inguinal ring. It is the most common cause of groin hernia.

# Presentation
In the fetus, the peritoneum gives a coat to the testicle as it passes through this ring, forming a temporary connection called the processus vaginalis. In normal development, the processus is obliterated once the testicle is completely descended.  The permanent coat of peritoneum that remains around the testicle is called the tunica vaginalis.  The testicle remains connected to its blood vessels and the vas deferens, which make up the spermatic cord and descend through the inguinal canal to the scrotum.
The internal inguinal ring, which is the beginning of the inguinal canal, remains as an opening in the internal oblique muscle, which forms the muscular outer wall for the spermatic cord.  When the opening is larger than necessary for passage of the spermatic cord, the stage is set for an indirect inguinal hernia.  The protrusion of peritoneum through the internal inguinal ring can be considered an incomplete obliteration of the processus.

# Causes
A hernia occurs when intra-abdominal contents, commonly including preperitoneal fatty tissues, abdominal fluid if present, the peritoneum itself, and eventually omentum 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, an opening in the external oblique fascia, into the scrotum.
A second means of indirect inguinal hernia formation in the spermatic cord is a failure of the processus vaginalis to close properly.  This second situation is very common in infants; in many cases the only abdominal contents found in the hernia are fluid.  This situation can sometimes be confused with a hydrocele, a collection of fluid around the testicle.  The difference is simple to determine; if there is communication between the peritoneum and the fluid, which defines the presence of a hernia, the fluid collection will change in size from time to time.  A hydrocoele, on the other hand, remains the same size.

# In females
In the female, groin hernias are only 4% as common as in males.  Indirect inguinal hernia is still the most common groin hernia for females.  If a woman has an indirect inguinal hernia, her internal inguinal ring is patent, which is abnormal for females.  The protrusion of peritoneum is not called "processus vaginalis" in women, as this structure is related to the migration of the testicle to the scrotum.  It is simply a hernia sac.  The eventual destination of the hernia contents for a woman is the labium majoris on the same side, and hernias can enlarge one labium dramatically if they are allowed to progress.

# Treatment
During herniorraphy, the surgeon recognizes the "indirect" hernia by noting that the hernia sac begins lateral to the inferior epigastric artery and vein, indicating that it arose at the top of the inguinal canal.