Anatomy of the Abdominal Wall
The abdominal wall is composed of 7 layers. They are (from
anterior to posterior) as follows:
Approximately midway between the umbilicus and the
symphysis pubis is an anatomic landmark known as the Semicircular Line of
Douglas. Because the anatomy of the abdominal wall differs above and below this
landmark, a description is appropriate and necessary when designing incisions or
attempting repairs in this part of the belly.
Above the Semicircular Line of Douglas, the anterior sheath
is formed by the fusion of the external oblique aponeurosis and the anterior
leaf of the internal oblique aponeurosis. The posterior sheath is formed by the
fusion of the posterior leaf of the internal oblique aponeurosis and the
aponeurosis of the transversus.
Below the Semicircular Line of Douglas, all three
aponeuroses cross anterior to the rectus muscle, leaving only the peritoneum and
the transversalis fascia between the rectus muscles and the contents of the
Anatomy of the Inguinal
The inguinal canal is a short passage that runs obliquely
and inferomedially through the inferior part of the anterior abdominal wall. It
runs parallel and slightly superior to the inguinal ligament. It is bounded by
two walls (anterior and posterior), a roof, and a floor.
The anterior wall is formed by the anterior aponeurosis of
the external oblique muscle with the addition of a small amount of the internal
The posterior wall is formed by transversalis fascia with
medial reinforcement by the conjoint tendon, which is the tendon of both the
internal oblique and transversus abdominis muscles.
Its floor is formed by the superior surfaces of both the
inguinal and lacunar ligaments
Its roof is formed by the arching fibers of the internal
oblique and transversus abdominis muscles.
The inguinal canal has two openings: the deep and
superficial inguinal rings.
The superficial (external) inguinal ring is a slitlike
opening in the aponeurosis of the external oblique muscle. The base of this
triangle is formed by the pubic crest and its sides are formed laterally by a
part of the external oblique aponeurosis, attached by the inguinal ligament to
the pubic tubercle, and medially by the part of the external oblique aponeurosis
attached to the pubic bone and crest. The sides are prevented from spreading
apart by intercrural fibers, named by the medial and lateral crura which it
From the superficial rings emerge the spermatic cords in
males or round ligaments in females, as well as the ilioinguinal nerve, which
supplies the skin on the superomedial aspect of the thigh.
The deep (internal) inguinal ring consists of a simple slit in the
transversalis fascia, located laterally to the inferior epigastric artery. Its
base is the midpoint of the inguinal ligament and its lateral edge is the origin
of the transversus abdominis muscle.
Blood Supply and Nerves
No discussion of the anatomy of the lower abdominal wall and
inguinal region would not be complete without mention of the blood supply and
nerves which traverse the area.
The Inferior Epigastric Artery and Vein originate from the
external iliac artery and vein and course superiorly entering the rectus sheath.
There, they course deep to the rectus abdominis muscles supplying the rectus
abdominus and medial portion of the anterolateral abdominal wall.
The Ilioinguinal Nerve originates from the ventral ramus of the
1st lumbar nerve. It passes between the 2nd and 3rd layers of abdominal
muscles, so continue on though the inguinal canal. This nerve supplies
innervation tot he skin of the scrotum (labia majorus in women), the mons pubis,
and adjacent medial aspect of the thigh. It also has distributions to the
internal oblique and transversus muscles of the abdomen.
During an open hernia repair, careful dissection of the
ilioinguinal nerve is important for two reasons. (1) Because of the
nerve distributions cited above, injury during incision or closure can result in
pain following the L1 dermatome (including the scrotum or labium majorum).
(2) Because the ilioinguinal nerve has motor distributions to the internal
oblique (which are inserted into the lateral border of the conjoint tendon),
division of the nerve paralyzes these muscle fibers, weakening the conjoint
tendon, which can precipitate a direct inguinal hernia.
||Inferior epigastric artery
||Inferior epigastric vein
||Ilioinguinal, iliohypogastric nerves
Hesselbach's triangle is an anatomic area of the abdominal wall
Laterally: The inferior epigastric
Medially: The lateral border of the rectus
space is important because it is through Hesselbach's Triangle that Direct
Hernia's leave the abdomen. Indirect Hernias protrude lateral to
The following terms are important to consider when talking about
Reducible: Refers to a hernia that can be moved
back into place easily (either manually or spontaneously)
Irreducible / Incarcerated: Refers to a hernia that cannot
be pushed back. It does not necessarily mean that the hernia is
strangulated or that obstruction is occurring (although both are possible).
If spontaneously reduced, and patient feels better, patient should be admitted
for close observation.
Strangulated: Refers to a hernia in which the blood supply
to the incarcerated viscus is compromised. Skin overlying the hernia is
typically erythematous and/or pale, and nausea, vomiting, fever, and abdominal
pain are usually present (or imminent. A strangulated hernia should not
be reduced, but if it is reduced (by patient or spontaneously), the patient
should be opened and the dead bowel removed.