Inguinal Canal

Overview

The inguinal canal is a short oblique passage in the inferior aspect of the anterior abdominal wall that transmits structures from the pelvis to the perineum and external genitalia. It is formed by the foetal migration of the gonads from the abdomen into the labioscrotal folds.

Boundaries

• Anterior wall – aponeurosis of the external oblique, reinforced by the internal oblique muscle laterally
• Posterior wall – transversalis fascia and conjoint (Henle’s) tendon
• Roof – transversalis fascia, internal oblique, and transversus abdominis
• Floor – inguinal ligament (a ‘rolled up’ portion of the external oblique aponeurosis), thickened medially by the lacunar ligament.

There are two openings to the inguinal canal known as rings.

Deep (internal) ring – located above the midpoint of the inguinal ligament, lateral to the epigastric vessels. The ring is created by the transversalis fascia, which invaginates to form a covering of the contents of the inguinal canal.

• Note: Not to be confused with the midinguinal point (midpoint between the pubic symphysis and the anterior superior iliac spine where the femoral pulse can be palpated)

Superficial (external) ring

• Located superolateral to the pubic tubercle.
• It is a triangle-shaped opening formed at the medial end of the external oblique aponeurosis by the evagination of the external oblique.
• Contains intercrural fibres, which run perpendicular to the aponeurosis of the external oblique and prevent the ring from widening.
  • Lateral crus of the ‘V’ is attached to the pubic tubercle
  • Medial crus of the ‘V’ is attached to the pubic crest, near the symphysis.
  • Posterior crus arises from the attachment of the lateral crus, whereby some fibres (reflected part of the inguinal ligament) pass up behind the cord to attach to the rectus sheath, blending with fibres of the opposite side

Contents

• Spermatic cord (males) – contains neurovascular and reproductive structures that supply and drain the testes.
  • Pampiniform plexus – drains into the testicular vein
  • Ductus deferens – a fibromuscular tube that is continuation of the epididymis and is an excretory duct of the testis
  • Cremasteric artery – arising from the inferior epigastric artery
  • Testicular artery – arising from the abdominal aorta below the level of the renal arteries (level of L2)
  • Artery of the ductus deferens (deferential artery) – arising from the superior vesical artery
  • Genital branch of the genitofemoral nerve
  • Sympathetic nerve fibres
  • Lymphatic vessels
• Round ligament (females) – originates from the uterine horn and travels through the inguinal canal to attach at the labia majora.
• Ilioinguinal nerve – branch of the lumbar plexus, contributes towards the sensory innervation of the genitalia
  • Only travels through part of the inguinal canal, exiting via the superficial inguinal ring (it does not pass through the deep inguinal ring)
  • At risk of damage during an inguinal hernia repair
• Genital branch of the genitofemoral nerve – supplies the cremaster muscle and anterior scrotal skin in males, and the skin of the mons pubis and labia majora in females.

Development

• During development, a fibrous cord of tissue called the gubernaculum attaches to the inferior portion of the gonad and guides descent of the gonads (testes or ovaries) from the posterior abdominal wall through the abdominal cavity to the scrotum (males) or labia (females)
• The inguinal canal is the pathway by which the testes leaves the abdominal cavity and enters the scrotum. In the embryological stage, the canal is flanked by an out-pocketing of the peritoneum (processus vaginalis) and the abdominal musculature.
• The processus vaginalis normally degenerates, but a failure to do so can cause an indirect inguinal hernia, a hydrocele, or interfere with the descent of the testes.
• The gubernaculum (once it has shortened in the process of the descent of the testes) becomes a small scrotal ligament, tethering the testes to the scrotum and limiting their movement.
• Females also have a gubernaculum, which attaches the ovaries to the uterus and labia majora. Because the ovaries are attached to the uterus by the gubernaculum, they are prevented from descending as far as the testes, instead moving into the pelvic cavity. The gubernaculum then becomes two structures in the adult: the ovarian ligament and round ligament of uterus

Variants

• Patent processus vaginalis
• Paradidymis