Inguinal canal

Structure

The inguinal canals are situated just above the medial half of the inguinal ligament. The canals are approximately 4 to 6 cm long, angled anteroinferiorly and medially. In males, its diameter is normally 2 cm (±1 cm) at the deep inguinal ring.

A first-order approximation is to visualize each canal as a cylinder.

Walls

To help define the boundaries, these canals are often further approximated as boxes with six sides. Not including the two rings, the remaining four sides are usually called the "anterior wall", "inferior wall ("floor")", "superior wall ("roof")", and "posterior wall". These consist of the following:

Deep inguinal ring

The deep inguinal ring (internal or deep abdominal ring, abdominal inguinal ring, internal inguinal ring, annulus abdominalis) is the entrance to the inguinal canal.

Location

The surface marking of the deep inguinal ring is classically described as at the midpoint of the inguinal ligament which is 0.5 inch above the inguinal ligament.

However, the surface anatomy of the point is disputed. In a recent study, it was found to be in a region between the mid-inguinal point (situated midway between the anterior superior iliac spine and the pubic symphysis) and the midpoint of the inguinal ligament (i.e. midway between the anterior superior iliac spine and the pubic tubercle). Traditionally, either one of these two sites was claimed as its location. However, this claim is based upon the study's dissection of 52 cadavers, and may not reflect the live in vivo anatomy.

Some sources state that it is at the layer of the transversalis fascia.

Description

The deep inguinal ring is an opening in the transversalis fascia. It is of an oval form, the long axis of the oval being vertical; it varies in size in different subjects, and is much larger in the male than in the female. It is bounded, above and laterally, by the arched lower margin of the transversalis fascia; below and medially, by the inferior epigastric vessels. It transmits the spermatic cord in the male and the round ligament of the uterus in the female.

From its circumference, a thin funnel-shaped membrane, the infundibuliform fascia, is continued around the cord and testis, enclosing them in a distinct covering.

Superficial inguinal ring

The superficial inguinal ring (subcutaneous inguinal ring or external inguinal ring) is an anatomical structure in the anterior wall of the mammalian abdomen. It is a triangular opening that forms the exit of the inguinal canal, which houses the ilioinguinal nerve, the genital branch of the genitofemoral nerve, and the spermatic cord (in men) or the round ligament (in women). At the other end of the canal, the deep inguinal ring forms the entrance.

It is found within the aponeurosis of the external oblique, immediately above the pubic crest, 1 centimeter above and superolateral to the pubic tubercle. It has the following boundaries—medial crura by pubic crest, lateral crura by pubic tubercle and inferiorly by inguinal ligament.

Contents

The structures which pass through the canals differ between males and females:

• in males: the spermatic cord and its coverings, and the ilioinguinal nerve.
• in females: the round ligament of the uterus, and the ilioinguinal nerve.

The classic description of the contents of the spermatic cords in the male are:

3 arteries: artery to vas deferens (or ductus deferens), testicular artery, cremasteric artery;

3 fascial layers: external spermatic, cremasteric, and internal spermatic fascia;

3 other structures: pampiniform plexus, vas deferens (ductus deferens), testicular lymphatics;

3 nerves: genital branch of the genitofemoral nerve (L1/2), sympathetic and visceral afferent fibres, ilioinguinal nerve (N.B. outside spermatic cord but travels next to it)

Note that the ilioinguinal nerve passes through the superficial ring to descend into the scrotum, but does not formally run through the canal.

Development

In males

During development, each testicle descends from the starting point on the posterior abdominal wall (para-aortically) from the labioscrotal swellings near the kidneys, down the abdomen, and through the inguinal canals to reach the scrotum. This way, each testicle descends through the abdominal wall into the scrotum behind the processus vaginalis (which later obliterates).