THE INGUINAL CANAL

The Inguinal Region The inguinal region is very important
surgically because it is the site of inguinal hernias. Although both sexes may get these, it is
much more common in males. The inguinal region is an area of
weakness in the anterior abdominal wall because of the prenatal penetration of
the wall by the testis and the spermatic cord. The Inguinal Canal This is an oblique passage, about 4 cm long in adults, through the inferior part of the anterior abdominal wall. It runs inferomedially, just superior and parallel to the medial half of the inguinal ligament. The inguinal canal has two walls (anterior and posterior), two openings (the superficial and deep inguinal rings), a roof (superior wall), and a floor (inferior wall). Owing to the obliquity of the inguinal
canal, the deep and superficial inguinal rings do not coincide. Increases in intra-abdominal pressure act
on the deep inguinal ring, which forces the posterior wall of the canal against
the anterior wall. Contraction of the external oblique muscle approximates the anterior wall of the canal with the posterior wall. Contraction of the internal oblique and transversus abdominis muscles causes the roof of the canal to descend and the passage is constricted. During standing, these muscles
continuous contract. During coughing and straining, the raise
intra-abdominal pressure threatens to
force some of the abdominal contents
through the canal, producing a hernia. However, vigorous contraction of the arched fleshy fibres of the internal oblique and transversus abdominis muscles "clamp down". The action is like a half-sphincter that helps prevent herniation. The conjoint tendon and rectus abdominis muscle also reinforce the superficial inguinal ring (as the external
oblique aponeurosis pushes against these
when intra-abdominal pressure rises). Back to top The Anterior Wall of the Inguinal Canal Formed mainly by the aponeurosis of the external oblique muscle. It is reinforced laterally by the fibres of
the internal oblique muscle; sometimes by the transversus abdominis muscle. The Posterior Wall of the Inguinal Canal Formed throughout by the transversalis fascia, which is reinforced medially by the conjoint tendon. The Floor of the Inguinal Canal This is formed by the superior surface of
the inguinal ligament and the lacunar ligament. The Roof of the Inguinal Canal It is formed by the arching fibres of the internal oblique and transversus abdominis muscles. The inferior epigastric artery lies at the medial boundary of the deep inguinal ring. Its pulsations form a useful landmark
during surgery for determining the
location of this ring. The Superficial Ring of the Inguinal
Canal This ring is more or less a triangular aperture (deficiency) in the aponeurosis of the external oblique muscle. The base of this triangle is formed by the public crest and the apex is directly superolateral. The sides of the triangle is formed by the medial and lateral crura (L. legs) of the superficial inguinal ring. Emerging from the superficial inguinal
ring is the spermatic cord in the male and the round ligament of the uterus in the female. In addition, the ilioinguinal nerve makes its exit through the ring to supply skin on
the superomedial aspect of the thigh. The central point of the superficial
inguinal ring is superior to the pubic tubercle. The superficial inguinal ring is just palpable superior and lateral to the
pubic tubercle. The Lateral Crus of the Superficial
Inguinal Ring This is formed by the part of the external oblique aponeurosis that is attached to the pubic tubercle via the inguinal
ligament. The spermatic cord rests on the inferior part of this crus. The Medial Crus of the Superficial Inguinal
Ring This is formed by the part of the external oblique aponeurosis that diverges to attach to the pubic bone and pubic crest,
medial to the pubic tubercle. Intercrural fibres from the inguinal ligament arch superomedially across the
superficial inguinal ring. These prevent the crura from spreading
apart. The Deep Ring of the Inguinal Canal This slit-like opening in the transversalis fascia is located just lateral to the inferior epigastric artery. The deep ring is immediately superior to
the midpoint of the inguinal ligament. The margins of the deep ring are not
sharply defined, as are those in the
superficial ring. Back to top The Spermatic Cord This cord suspends the testis in the
scrotum and consists of the structures
running to and from the testis. They are surrounded by protective
coverings derived from the anterior abdominal wall. The spermatic cord begins at the deep inguinal ring, lateral to the inferior epigastric artery, where its constituents assemble, and ends at the posterior
border of the testis. It passes through the inguinal canal, emerges at the superficial inguinal ring, and descends within the scrotum to the
testis. As the cord leaves the inguinal canal, it acquires its 3rd covering, the external spermatic fascia. Constituents of the Spermatic Cord 1. The Ductus Deferens This is the large duct of the testis,
formerly called the vas deferens. It lies in the posterior part of the
spermatic cord and is easily palpable
because of its thick wall of smooth
muscle. 2. Arteries The testicular artery arises from the anterior aspect of the aorta at the level
of L2 vertebrae. This is the main artery supplying the
testis and the epididymis. The artery of the ductus deferens is a slender vessel that arises from the
inferior vesical artery. It accompanies the ductus deferens throughout its course and anastomoses
with the testicular artery near the testis. The cremasteric artery is a small vessel that arises from the inferior epigastric
artery. It supplies the cremaster muscle and other coverings of the spermatic cord. 3. Veins Up to 12 veins leaving the posterior surface of the testis anastomose to form
a pampiniform plexus (L. pampinus, tendril). This large vine-like plexus forms a large part of the spermatic cord, surrounding
the ductus deferens and arteries in the spermatic cord. 4. Nerves There are sympathetic fibres on the
arteries and both sympathetic and
parasympathetic fibres on the ductus deferens. The genital branch of the genitofemoral nerve passes into the spermatic cord and supplies the cremaster muscle. 5. Lymph Vessels Lymph vessels draining the testis and
immediately associated structures pass
superiorly in the spermatic cord. These vessels end in the lumbar and preaortic lymph nodes. Back to top Coverings of the Spermatic Cord The spermatic cord is covered by three
layers of fascia, derived from the anterior abdominal wall. The Internal Spermatic Fascia As the processus vaginalis
(embryological) evaginated the
transversalis fascia at the deep inguinal ring, it carried a thin layer of fascia that became the internal spermatic fascia. It constitutes the filmy innermost covering of the spermatic cord. The Cremaster Muscle and Cremasteric
Fascia As the processus vaginalis, with its
covering of transversalis fascia
evaginated under the edge of the internal oblique muscle, it acquired some of this muscle's fibres and its investing
fascia. These fibres form the cremaster muscle
and cremasteric fascia. The cremasteric fascia forms the middle
covering of the spermatic cord, which
contains loops of the cremaster muscle. The cremaster muscle, which is
continuous with the internal oblique muscle, reflexly draws the testis to a more superior position in the scrotum (cremasteric reflex), particularly in cold
temperatures. The External Spermatic Fascia As the external oblique muscle was evaginated by the processus vaginalis, it
formed the superficial inguinal ring and
an extension of its aponeurosis was
carried outward. This layer became the external spermatic
fascia, the thin outermost covering of the spermatic cord. The Inguinal Region The inguinal region is very important
surgically because it is the site of inguinal hernias. Although both sexes may get these, it is
much more common in males. The inguinal region is an area of
weakness in the anterior abdominal wall because of the prenatal penetration of
the wall by the testis and the spermatic cord. The Inguinal Canal This is an oblique passage, about 4 cm long in adults, through the inferior part of the anterior abdominal wall. It runs inferomedially, just superior and parallel to the medial half of the inguinal ligament. The inguinal canal has two walls (anterior and posterior), two openings (the superficial and deep inguinal rings), a roof (superior wall), and a floor (inferior wall). Owing to the obliquity of the inguinal
canal, the deep and superficial inguinal rings do not coincide. Increases in intra-abdominal pressure act
on the deep inguinal ring, which forces the posterior wall of the canal against
the anterior wall. Contraction of the external oblique muscle approximates the anterior wall of the canal with the posterior wall. Contraction of the internal oblique and transversus abdominis muscles causes the roof of the canal to descend and the passage is constricted. During standing, these muscles
continuous contract. During coughing and straining, the raise
intra-abdominal pressure threatens to
force some of the abdominal contents
through the canal, producing a hernia. However, vigorous contraction of the arched fleshy fibres of the internal oblique and transversus abdominis muscles "clamp down". The action is like a half-sphincter that helps prevent herniation. The conjoint tendon and rectus abdominis muscle also reinforce the superficial inguinal ring (as the external
oblique aponeurosis pushes against these
when intra-abdominal pressure rises). Back to top The Anterior Wall of the Inguinal Canal Formed mainly by the aponeurosis of the external oblique muscle. It is reinforced laterally by the fibres of
the internal oblique muscle; sometimes by the transversus abdominis muscle. The Posterior Wall of the Inguinal Canal Formed throughout by the transversalis fascia, which is reinforced medially by the conjoint tendon. The Floor of the Inguinal Canal This is formed by the superior surface of
the inguinal ligament and the lacunar ligament. The Roof of the Inguinal Canal It is formed by the arching fibres of the internal oblique and transversus abdominis muscles. The inferior epigastric artery lies at the medial boundary of the deep inguinal ring. Its pulsations form a useful landmark
during surgery for determining the
location of this ring. The Superficial Ring of the Inguinal
Canal This ring is more or less a triangular aperture (deficiency) in the aponeurosis of the external oblique muscle. The base of this triangle is formed by the public crest and the apex is directly superolateral. The sides of the triangle is formed by the medial and lateral crura (L. legs) of the superficial inguinal ring. Emerging from the superficial inguinal
ring is the spermatic cord in the male and the round ligament of the uterus in the female. In addition, the ilioinguinal nerve makes its exit through the ring to supply skin on
the superomedial aspect of the thigh. The central point of the superficial
inguinal ring is superior to the pubic tubercle. The superficial inguinal ring is just palpable superior and lateral to the
pubic tubercle. The Lateral Crus of the Superficial
Inguinal Ring This is formed by the part of the external oblique aponeurosis that is attached to the pubic tubercle via the inguinal
ligament. The spermatic cord rests on the inferior part of this crus. The Medial Crus of the Superficial Inguinal
Ring This is formed by the part of the external oblique aponeurosis that diverges to attach to the pubic bone and pubic crest,
medial to the pubic tubercle. Intercrural fibres from the inguinal ligament arch superomedially across the
superficial inguinal ring. These prevent the crura from spreading
apart. The Deep Ring of the Inguinal Canal This slit-like opening in the transversalis fascia is located just lateral to the inferior epigastric artery. The deep ring is immediately superior to
the midpoint of the inguinal ligament. The margins of the deep ring are not
sharply defined, as are those in the
superficial ring. Back to top The Spermatic Cord This cord suspends the testis in the
scrotum and consists of the structures
running to and from the testis. They are surrounded by protective
coverings derived from the anterior abdominal wall. The spermatic cord begins at the deep inguinal ring, lateral to the inferior epigastric artery, where its constituents assemble, and ends at the posterior
border of the testis. It passes through the inguinal canal, emerges at the superficial inguinal ring, and descends within the scrotum to the
testis. As the cord leaves the inguinal canal, it acquires its 3rd covering, the external spermatic fascia. Constituents of the Spermatic Cord 1. The Ductus Deferens This is the large duct of the testis,
formerly called the vas deferens. It lies in the posterior part of the
spermatic cord and is easily palpable
because of its thick wall of smooth
muscle. 2. Arteries The testicular artery arises from the anterior aspect of the aorta at the level
of L2 vertebrae. This is the main artery supplying the
testis and the epididymis. The artery of the ductus deferens is a slender vessel that arises from the
inferior vesical artery. It accompanies the ductus deferens throughout its course and anastomoses
with the testicular artery near the testis. The cremasteric artery is a small vessel that arises from the inferior epigastric
artery. It supplies the cremaster muscle and other coverings of the spermatic cord. 3. Veins Up to 12 veins leaving the posterior surface of the testis anastomose to form
a pampiniform plexus (L. pampinus, tendril). This large vine-like plexus forms a large part of the spermatic cord, surrounding
the ductus deferens and arteries in the spermatic cord. 4. Nerves There are sympathetic fibres on the
arteries and both sympathetic and
parasympathetic fibres on the ductus deferens. The genital branch of the genitofemoral nerve passes into the spermatic cord and supplies the cremaster muscle. 5. Lymph Vessels Lymph vessels draining the testis and
immediately associated structures pass
superiorly in the spermatic cord. These vessels end in the lumbar and preaortic lymph nodes. Back to top Coverings of the Spermatic Cord The spermatic cord is covered by three
layers of fascia, derived from the anterior abdominal wall. The Internal Spermatic Fascia As the processus vaginalis
(embryological) evaginated the
transversalis fascia at the deep inguinal ring, it carried a thin layer of fascia that became the internal spermatic fascia. It constitutes the filmy innermost covering of the spermatic cord. The Cremaster Muscle and Cremasteric
Fascia As the processus vaginalis, with its
covering of transversalis fascia
evaginated under the edge of the internal oblique muscle, it acquired some of this muscle's fibres and its investing
fascia. These fibres form the cremaster muscle
and cremasteric fascia. The cremasteric fascia forms the middle
covering of the spermatic cord, which
contains loops of the cremaster muscle. The cremaster muscle, which is
continuous with the internal oblique muscle, reflexly draws the testis to a more superior position in the scrotum (cremasteric reflex), particularly in cold
temperatures. The External Spermatic Fascia As the external oblique muscle was evaginated by the processus vaginalis, it
formed the superficial inguinal ring and
an extension of its aponeurosis was
carried outward. This layer became the external spermatic
fascia, the thin outermost covering of the spermatic cord.