Transcript Dissection of Anterior Abdominal Wall

Dissection of
Anterior Abdominal
Wall
With the cadaver in the supine position, incise the skin
in the midline from the xiphisternal joint to the pubic
symphysis, cutting around the umbilicus. Then incise
the skin 1 inch above the pubis symphysis laterally over
to and a little above the iliac crest to the midaxillary line
on both sides. Reflect the skin from the midline
anteriorlly to the midaxillary line, leaving the superficial
fascia on the anterior abdominal wall.
Identify the fatty layer of the superficial
fascia ( Camper's fascia)and note that it is
continuous below with the fatty superficial
fascia of the thigh and above with the
superficial fascia of the thorax. Note that
the fat is greatest in amount over the
inferior half of the abdomen.
Note also the terminal portion of the
superficial arteries and cutaneous
nerves in this layer; also observe the
superficial veins.
Identify the Membranous Layer of the
Superficial Fascia (Scarpa's Fascia). Note
That It Lies Deep to the Fatty Layer and
Immediately Superficial to the aponeurosis
of the External Oblique Muscle. Insert a
Finger Between the Membranous Layer
and the aponeurosis of the External
Oblique and Separate Them Inferiorly.
Note That the Finger Can Be Passed
Down Medial to the Pubic Tubercle Along
the Spermatic Cord and Anterior to the
Body of the Pubis Into the
Perineum.Lateral to the Pubic Tubercle
the Finger Cannot Enter the Thigh,
However,since the Membranous Layer Is
Attached to the Deep Fascia of the Thigh
Just Below the Inguinal Ligament.
Identify the Superficial Inguinal
Ring Above the Pubic Tubercle but
Do Not Disturb It at This Stage.
The Ring Is a Triangular Opening
in the aponeurosis of the External
Oblique Muscle.
Make a vertical incising through the full
thichness of the superficial fascia from the
xiphoid process to the symphysis pubis.
With the aid of a scalpel handle, carefully
reflect the flaps of fascia laterally,
separating the fascia from the aponeurosis
of the external oblique muscle.
Identify examples of anterior and
lateral cutaneous nerves. Remove
all the flaps of superficial fascia
by making a vertical incision
through the fascia in the
midaxillary line.
External oblique muscle.
Clean the surface of the external oblique
muscle and its aponeurosis. Note the
attachment of the fleshy origin from each
of the lower eight ribs. Here it interdigitates
with the origin of the serratus anterior and
the latissimus dorsi.
Observe the direction of the muscle
fibers. Identify the linea alba that
extends from the xiphoid process
down to the symphysis pubis and is
formed by the fusion of the
aponeurosis of the muscle of the two
sides.
Carefully define the margins of the superficial
inguinal ring lying above the pubic tubercle.
Note that it is triangular in shape and not
round. In the male, identify the spermatic cord
emerging from this aperture and confirm that
its outer covering, the external spermatic
fascia, is attached to the margins of the ring.
In the female, the round ligament of the
uterus emerges from the ring. Again
confirm that its outer covering is attached to
the margin of the ring. Identify the
ilioinguinal nerve as it emerges from the
lateral part of the superficial inguinal ring.
Identify the inguinal ligament and note that
it is formed by the lower margin of the
aponeurosis of the external oblique muscle.
The ligament is attached laterally to the
anterior superior iliac spine and medially to
the pubic tubercle. Attached to the lower
margin of the ligament is the deep fascia.
Internal Oblique Muscle.
Free the interdigitating origins of the external
oblique muscle from those of the serratus anterior as
far as the midaxillary line. Incise the external oblique
down the midaxillary line to the iliac crest. Now find
the plane between the external oblique and the
internal oblique muscles. With the fingers, free the
external oblique from the internal oblique and
gradually turn the upper part of the external oblique
forward.
Note that the fibers of the internal oblique
muscle run downward and backward, that is, at
right angles to the fibers of the external oblique.
Continue to reflect the external oblique forward
and medially toward the lateral margin of the
rectus sheath to fully expose the underlying
internal oblique muscle. Study the origins and
insertions of the external oblique and its
innervation.
Make a vertical incision through the
aponeurosis of the external oblique muscle
1 inch lateral to the rectus sheath and
extend it down to a point 3 inches above the
pubic tubercle. Turn the inferior portion of
the external oblique downward and
carefully examine the superior surface of
the inguinal ligament.
It is most important that you understand the
attachments and configuration of the
inguinal ligament. Note that the ligament is
the inrolled lower margin of the aponeurosis
of the external oblique and confirm again
that it is attached to the pubic tubercle
medially and the anterior superior iliac
spine laterally.
Carefully follow the inguinal ligament medially
to the pubic tubercle, follow the fibers backward
as the lacunar ligament, and note the attachment
to the pectineal line. Note the continuity of the
lacunar ligament with the pectineal ligament.
Study the relationship of the inguinal, lacunar,
and pectineal ligaments to the femoral sheath.
Clean the surface of the internal oblique muscle.
Define the inferior border of the muscle and note
its relationship to the spermatic cord or round
ligament of the uterus. Study closely the origin of
the internal oblique from the inguinal ligament.
Note that the internal oblique fibers arise from
the lateral half of the ligament and therefore lie
anterior to the deep inguinal ring.
Identify the cremaster muscle
passing onto the spermatic cord
from the lower edge of the internal
oblique muscle. Clean the
ilioinguinal nerve and follow it
proximally to where it emerges from
the internal oblique muscle.
Exposure of transversus abdominis
muscle. Cut through the attachments
of the internal oblique muscle to the
costal margin and transect it
vertically along the midaxillary line.
Cut through the origin from the iliac
crest and the inguinal ligament.
Insert your fingers into the plane between the
internal oblique and underlying transversus
abdominis muscle. Reflect the internal
oblique muscle forward to the lateral margin
of the rectus sheath to expose fully the
underlying transversus abdominis muscle
and the intercostal neres.
At the lateral edge of the rectus abdominis, the
aponeurosis of the internal oblique is seen to
split and pass anterior and posterior to the
rectus abdominis; the anterior layer fuses with
the aponeurosis of the external oblique muscle,
and posterior layer fuses with that of the
transversus abdominis. This aponeurotic
covering to the rectus abdominis is called the
rectus sheath.
Transversus abdominis muscle.
Clean the surface of the transversus abdominis
and the vessels and nerves that lie on it. Note
that the fibers of the transversus muscle run in a
horizontal direction. Identify the lower margins
of the transversus abdominis muscle and follow
its fibers medially to join with those of the
internal oblique to form the conjoint tendon.
Examine the attachment of the conjoint
tendon to pubic crest and the pectineal line.
Note that the conjoint tendon lies
immediately posterior to the superficial
inguinal ring. Again examine the inguinal,
lacunar, and pectineal ligaments and note
their relationship to the conjoint tendon.
Fascia transversalis.
Insert the handle of the scalpel between the
lower margin of the transversus abdominis
muscle and the underlying fascia
transversalis. Remember that this fascia
lines the abdominal wall and forms the
posterior wall of the inguinal canal lateral
to the conjoint tendon.
The fascia transversalis is tissuepaper thin, and the extraperitoneal
fat can be seen through it. Deep to
the fat is the peritoneal lining of
the abdominal cavity.
Rectus Sheath.
The rectus sheath is a long sheath that encloses
the rectus abdominis muscle and pyramidalis
muscle (if present) and contains the anterior
rami of the lower six thoracic nerves and the
superior and inferior epigastric vessels and
lymphatics. It is formed largely by the
aponeurosis of the three anterolateral
abdominal muscles.
Open the entire length of the rectus sheath by a
longitudinal incision just lateral to the linea alba.
Identify the medial edge of the rectus abdominis
muscle. Raise its medial edge and, with the
finger or blunt end of the forceps, verify that it is
possible to separate the rectus muscle from the
posterior layer of the sheath.
Note and preserve the nerves and
vessels passing through the
posterior wall of the sheath into
the lateral part of the muscle.
Reflect the lateral part of the anterior layer of
the sheath by cutting free the attached tendinous
intersections of the rectus muscle. Examine
again the linea alba and realize that it is formed
by the fusion of the aponeuroses of the three
lateral muscles of the abdominal wall on the two
sides. It extends from the xiphoid process down
to the sympgysis pubis and separates the rectus
abdominis muscles on the two sides.
Understand What Is Meant by the
Term linea semilunaris. This Is a
Curved Ridge Formed by the
Lateral Margin of the rectus
abdominis Muscle.
Clean the rectus abdominis and Identify the
pyramidalis Muscle if Present. Transect the
rectus Muscle at Its Middle and Raise the Upper
and Lower Ends, Cutting the Nerves That Enter
It. Identify the Superior epigastric Artery That
Enters the rectus Sheath by Emerging From
Beneath the Lower Margin of the Seventh Costal
Cartilage and Passing Down Posterior to the
rectus Muscle.
Note also the inferior epigastric
artery that ascends within the sheath
from below. Verify the origin and
insertion of the rectus abdominis
and the pyramidalis muscles.
Finally,remove both of these
muscles.
Carefylly examine the anterior and osterior walls
of the rectus sheath and verify their formation
from the aponeuroses of the anterior abdominal
muscles. Note that the posterior wall ends below
at the arcuate line, where the aponeuroses of the
internal oblique and trasversus abdominis
muscles pass anterior to the rectus muscle.
Cut free the attachments of the internal oblique and
trasversus abdominis muscles from the costal margin.
Incise the latter muscle along the midaxillary line to the
iliac crest. Try to preserve the underlying peritoneum
intact. Reflect all the abdominal muscles and the fascia
transversalis inferiorly as a unit by blunt dissection.
Cut around the umbilicus to preserve its connection
with the ligamentum teres of the liver.
Deep inguinal ring.
Before destroying the fascia transversalis in the inguinal
region, pull on the spermatic cord or round ligament of
the uterus from the anterior surface and identify the
deep inguinal ring and the internal spermatic fascia.
Confirm that the deep ring lies lateral to the inferior
epigastric vessels.
The Abdominal Cavity
Peritoneum.
The peritoneum is a serous membrane
lining the walls of the abdominal
cavity and clothing the abdominal
viscera. The parietal peritoneum
lines the walls of the abdominal
cavity, and the visceral peritoneum
covers the abdominal organs.
The peritoneum secretes a small
amount of serous fluid, which
lubricates the surfaces of the
peritoneum and facilitates free
movement between the viscera. The
potential space between the parietal
and visceral layers of the peritoneum
is called the peritoneal cavity.
The peritoneum has the following important
arrangements:
1. The peritoneal cavity is divided into the
greater and the lesser sac. The greater sac is
the main compartment, and it extends across the
whole breadth of the abdomen and from the
diaphragm to the pelvis. The lesser sac is the
smaller compartment, and it lies behind the
stomach, as a diverticulum from the greater sac;
it opens through an oval window called the
opening of the lesser sac, or the epiploic
foramen.
2. A mesentery is a twolayered fold of peritoneum
that attaches part of the
intestines to the posterior
abdominal wall, and it includs
the mesentery of the small
intestine, the transvers
mesocolon, and the sigmoid
mesocolon.
3. An omentum is a two-layered fold of
peritoneum that attaches the stomach to
another viscus. The greater omentum is
attaches to the greater curvature of the
stomach, and it hangs down like an apron
in the space between the coils of small
intestine and the anterior abdominal wall.
It is folded back on itself
and is attached to the
inferiorborder of the
transverse colon. The lesser
omentum slings the lesser
curvature of the stomach to
the undersurface of the liver.
The gastrosplenic omentum
(ligament) connects the
stomach to the spleen
.
4. The peritoneal ligaments are two-layered
folds of peritoneum that attach the less
mobile solid viscera to the abdominal walls.
The liver, for example, is attached by the
falciform ligament to the anterior abdominal
wall and to the undersurface of the diaphragm.
The mesenteries, omenta, and peritoneal
ligaments allow blood vessels, lymphatics,
and nerves to reach the various viscera.
Opening of Abdominal cavity
and Inspection of Its
Contents.
When the peritoneal cavity has been opened by
making a transverse incision through the
parietal peritoneum lining the anterior
abdominal wall at the level of the umbilicus,
identify three folds of peritoneum that
converge on the umbilicus from below. These
cover the two lateral umbilical ligaments and
the median umbilical ligament .
Below the level of the
anterior superior iliac spines,
two additional folds may be
recognized, due to the
underlying inferior epigastric
arteries.
Examine the falciform ligament, which extends
from the umbilicus to the liver. Identify the
ligamentum teres in the free margin of the
falciform ligament. Cut the peritoneum along
the costal margin, except where the falciform
ligament of the liver is attached. Reflect
the remainder of the peritoneum inferiorly by
cutting it down the midaxillary line on each
side.
Study the abdominal viscera in
situ. Note the relative size,
shape, and position of all the
abdominal organs in the
undisturbed abdominal cavity.
It is important to avoid any
dissection at this stage.
Be prepared to find pathological
changes that may have been
responsible for the person's death
or that may be evidence of previous
disease. For example, the
peritoneum may be studded by
numerous secondary carcinomatous
deposits that have spread from a
primary lesion in one of the
abdominal organs.
Identify the following
structures:
1. The liver, which is divided
into right and left lobes by
the falciform ligament.
2. The fundus of the
gallbladder, which projects
beneath the lower margin of the
liver.
3. The stomach, which lies in
the epigastrium. It is
connected to the liver by the
lesser omentum.
4. The greater omentum, which
contains a large quantity of
fat. Free up the greater
omentum and reflect it
superiorly to expose the
transverse colon.
5. The spleen, which lies in the
left hypochondrium behind the
stomach and in contact with the
diaphragm.
6. The coils of small intestine. Pull the
greater omentum
upward over the costal margin
and identify the coils of jejunum in the upper
left part of the abdominal cavity and the coils
of ileum in the lower right part of the cavity.
7. The large intestine. The cecum is a
blind pouch that lies below the level
of the ileocolic junction in the right
iliac region. Identify the appendix on
its posteromedial surface. The cecum is
continuous above with the ascending
colon, then transverse colon, then
descending colon and sigmoid colon.