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Structure of the abdominal wall
The abdomen is the region of the trunk that lies
between the diaphragm above which separate
it from the thoracic wall and the inlet of the
pelvis below which communicates it with the
pelvis.
Anteriorly, the abdominal wall is formed above
by the lower part of the thoracic cage &
below by the rectus abdominis ;external
oblique ; internal oblique and transversus
abdominis muscles and fasciae.
Posteriorly , the abdominal wall is formed
in the midline by the 5 lumbar vertebrae &
their intervetebral discs.
Laterally,it is formed by the 12th rib ; the upper
part of bony pelvis with the iliacus muscles;
psoas muscles; quadratus lumborum muscles
and the aponeuroses of origin of the
transversus abdominis muscles .
The abdominal wall are lined by a fascial
envelope & the parietal peritoneum.
Anterior abdominal wall
It is made up of skin; superficial fascia;
deep fascia; muscles; extraperitoneal
fascia and parietal peritoneum.
Skin
It is loosely attached to the underlying
structures except at the umbilicus where it
is tethered to the scar tissue.
The natural lines of cleavage rows of the
skin are constant and run downward &
forward almost horizontally around the trunk.
Superficial Fascia
It can be divided into a superficial fatty
layer ( fascia of Camper ) & a deep
membranous layer ( Scarpa’s fascia ) .
The fatty layer is continuous with the
superficial fat over the rest of the body and
may be thick 8cm ( 3 inch ) or more in
obese patients.
In the scrotum, it is represented as a thin
layer of smooth muscle ( Dartos muscle ).
The membranous layer
It is thin & fades out laterally and above where it
becomes continuous with the superficial fascia
of the back and thorax.
Inferiorly , it passes onto the front of the thigh
where it fuses with the deep fascia one
fingerbreadth below the inguinal ligament.
In the midline inferiorly , it is not attached to the
pubis but forms a tubular sheath for the penis
or clitoris .
Below , in the perineum, it enters the wall of the
scrotum or labia majora. From there it passes to
be attached on each side to the margins of the
pubic arch. It is here referred to as Colles’s
fascia.
Posteriorly, it fuses with the perineal body & the
posterior margin of the perineal membrane
In the scrotum, it persists as a separate layer.
Deep fascia:
It is a thin layer of connective tissue covering
the muscles. It lies immediately deep to the
membranous layer of superficial fascia.
Clinical Notes
1- Surgical Incisions
All surgical incisions should be made in the
line of cleavage ( direction of the rows of the
collagen fibers ) in the dermis. These fibers
run in parallel rows. An incision along a
cleavage line will heal as a narrow scar,
whereas one that crosses the lines will heal
as wide or heaped- up scars ( ugly ).
2- Extravasation of urine
Rupture of penile urethra may be followed
by extravasation of urine into the scrotum,
perineum and penis and then up into the
lower part of the anterior abdominal wall
deep to the membranous layer of fascia.
The urine is excluded from the thigh
because of the attachment of the fascia to
the fascia lata.
Muscles of the Anterior Abdominal Wall
They are 3 broad thin sheets that are aponeurotic in front. From exterior to interior
they are the external oblique ; internal oblique and transversus abdominis.
The rectus abdominis ,a wide vertical muscle that lies on either side of the midline.
Anteriorly, as the aponeuroses of the 3 muscles sheets pass forward , they enclose
the rectus abdominis to form the rectus sheath. The lower part of the rectus sheath
contains pyramidalis muscle.
External oblique
It is a broad ; thin ; muscular sheet that arises
from the outer surfaces of the lower 8th ribs
and fans out to be inserted into the xiphoid
process ; linea alba ; pubic crest; pubic
tubercle and the anterior half of the iliac
crest.
Most of the fibers are inserted by means of a
broad aponeurosis.
A triangular- shaped defect in the external
oblique aponeurosis lies above & medial to
the pubic tubercle (Superficial inguinal ring
)
The spermatic cord or round ligament of the
uterus passes through this opening and carries
the external spermatic fascia or the external
covering of the round ligament of the uterus
from the margins of the ring.
Between the anterior superior iliac spine &
the pubic tubercle, the lower border of the
aponeurosis is folded backward on itself,
forming the inguinal ligament
From the medial end of the inguinal
ligament, the lacunar ligament
extends backward & upward to the
pectineal line on the superior ramus
of the pubis.
The sharp , free crescentric edge of
the lacunar ligament forms the
medial margin of the femoral ring.
On reaching the pectineal line , the
lacunar ligament becomes
continuous with a thickening of the
periosteum called the pectineal
ligament.
The lateral part of the posterior edge
of the inguinal ligament gives origin
to part of the internal oblique &
transversus abdominis muscles.
The inferior rounded border of the
inguinal ligament is attached to the
deep fascia of the thigh ( fascia lata ).
Internal Oblique
It is a broad, thin , muscular sheet that
lies deep to the external oblique .
It arises from the lumbar fascia, the
anterior two thirds of the iliac crest
and the lateral two thirds of the
inguinal ligament. Its fibers radiate
as they pass upward & forward.
It is inserted into the lower borders of
the lower 3 ribs & their costal
cartilages ( lower 5 ribs ); the xiphoid
process; the linea alba and the
symphysis pubis.
It has a lower free border that arches
over the spermatic cord or the round
ligament and then descends behind
it to be attached to the pubic crest &
the pectineal line.
Near their insertion , the lowest
tendinous fibers are joint by similar
fibers from the transversus abdominis
to form the conjoint tendon.
The conjoint tendon is attached
medially to the linea alba . It has a
lateral free border.
As the spermatic cord or round
ligament passes under the lower
border of the internal oblique ,it
carries with it some of the muscle
fibers that are called the cremaster
muscle.This muscle passes inferiorly as
a covering of the spermatic cord and
enters the scrotum.
The cremasteric fascia is the term used
to describe the cremaster muscle & its
fascia.
Transversus muscle
It is a thin sheet of muscle that lies deep to the internal oblique . Its fibers run
horizontal forward. It arises from the deep surface of the lower 6 costal cartilages.
( interdigitating with the diaphragm ); the lumbar fascia ; anterior two thirds of the
iliac crest and the lateral third of the inguinal ligament.
It is inserted into the xiphoid process ; linea alba and the symphysis pubis.
N.B. The posterior border of the internal oblique & transversus muscles are
attached to the lumbar vertebrae by the lumbar fascia.
Rectus Abdominis
It is a long strap muscle that extends along the whole length of the anterior
abdominal wall. It is broader above and lies close to the midline which it is separated
from it by the linea alba ( strong avascular fibrous tissue ).
It arises by 2 heads from the front of the symphysis pubis & from the pubic crest.
It is inserted into the 5th 6th and 7th costal catilages & xiphoid process.
N.B. pyramidalis muscle lies in front of the lower part of the rectus abdominis. It
arises by its base from the anterior surface of the pubis and is inserted into
the linea alba.
Its lateral margin forms a curved
ridge that can be palpated and often
seen when it contracts ; it is termed
the linea semilunaris which extends
from the tip of the 9th costal
cartilage to the pubic tubercle.
The rectus abdominis muscle is
divided into distinct segments by 3
transverse tendinous intersections.
One at the level of the xiphoid
process ; one at the level of the
umbilicus and one halfway between
these two. These intersections are
strongly attached to the anterior
wall of the rectus sheath.
The rectus abdominis is enclosed
between the aponeuroses of the
external & internal oblique and
transversus muscles which form the
rectus sheath.
Rectus Sheath
It is a long fibrous sheath that encloses the rectus abdominis muscle & pyramidalis and
contains the anterior rami of the lower 6 thoracic nerves & the superior and inferior
epigastric vessels & lymph vessels. It is formed by the aponeuroses of the 3 lateral
abdominal muscles. It has 3 levels for the description:
1- Above the costal margin, the anterior wall is formed by the aponeurosis of the
external oblique. The posterior wall is formed by the thoracic wall ( 5th; 6th and 7th
costal cartilages & the intercostal spaces ).
2- Between the costal margin & the anterior superior iliac spine, the aponeurosis of the
internal oblique splits to enclose the rectus muscle & the external oblique aponeurosis
is directed in front of the muscle & the transversus abdominis is directed behind the
3- Between the level of the anterosuperior
iliac spine & the pubis , the aponeurosis of
all 3 muscles form the anterior wall. The
posterior wall is absent & the rectus muscle
lies in contact with the fascia transversalis.
Its posterior wall has a free curved lower
border called the arcuate line. At this site,
the inferior epigastric vessels enter the
rectus sheath & pass upward to anastomose
with the superior epigastric vessels.
It is separated from its fellow on the opposite
side by a fibrous band called the linea alba
which extends from the xiphoid process
down to the symphysis pubis & is formed by
the fusion of the aponeurosis of the lateral 3
muscles of the 2 sides .
Its posterior wall is not attached to the rectus
abdominis muscle but its anterior wall is
firmly attached to it by the muscle’s
tendinous intersections.
Function of the Anterior Abdominal Wall
1- The oblique muscles laterally flex & rotate the trunk.
2- The rectus abdominis flexes the trunk & stabilizes the pelvis .
3- The pyramidalis keeps the linea alba taut during the process.
4- The muscles of the anterior & lateral abdominal walls assist the diaphragm
during inspiration by relaxing as the diaphragm descends .
5- They assist in the act of forced expiration that occurs during coughing and
sneezing by pulling down the ribs & sternum.
6- Their tone plays an important part in supporting the abdominal viscera.
7-They increase the intra-abdominal pressure & help in micturition, defecation,
vomiting and parturition.
Nerve Supply of Anterior Abdominal Wall Muscles
1- The oblique & transversus abdominis muscles are supplied by the lower
6 thoracic nerves & ilioinguinal and iliohypogastric nerves.
2- The rectus abdominis is supplied by the lower 6 thoracic nerves.
3- The pyramidalis is supplied by the 12th thoracic nerve.
Fascia Transversalis
It is a thin layer of fascia that lines the
transversus abdominis muscle and is
continuous with a similar layer lining the
diaphragm and the iliacus muscle.
Extraperitoneal Fat
It is a thin layer of connective tissue that
contains fat and lies between the fascia
transversalis and the parietal peritoneum.
Parietal Peritoneum
It is a serous membrane that lines the walls of
the abdomen and is continuous below with
the parietal peritoneum lining the pelvis.
N.B. 1- The fascia transversalis , the
diaphragmatic fascia , the iliacus
fascia and the pelvic fascia form
one continuous lining to the
abdomen and pelvis.
2- The femoral sheath is formed from
the fascia transversalis & fascia iliaca.
Nerves of the Anterior Abdominal Wall
They are the anterior rami of the lower 6 thoracic & the first lumbar nerves. The 6th
thoracic nerve is called the subcostal nerve while the other 5 nerves are called
intercostal nerves. The 1st lumbar is the iliohypogastric & ilioinguinal nerves.
They pass forward in the interval between the internal oblique & the transversus
muscles.
They supply the skin of the anterior abdominal wall & the muscles and the parietal
peritoneum.
The lower 6 thoracic nerves pierce the posterior wall of the rectus sheath to supply
the rectus & pyramidalis muscles. They terminate by piercing the anterior wall of
the sheath and supplying the skin.
The 1st lumbar nerve does not enter the rectus sheath.
The iliohypogastric nerve, pierces the external obligue aponeurosis above the
superficial inguinal ring.
The ilioinguinal nerve emerges through the ring.
They end by supplying the skin just above the inguinal ligament & symphysis
pubis.
The dermatome of T7 is located in the epigastrium over the xiphoid process.
The dermatome of T10 includes the umbilicus and that of L1 lies just above the
Arteries of the Anterior Abdominal Wall
1-The superior epigastric artery, is one of
the terminal branches of the internal
thoracic artery that enters the upper part
of the rectus sheath between the sternal &
costal origins of the diaphragm.
It descends behind the rectus muscle
supplying the upper central part of the
anterior abdominal wall and anastomoses
with the inferior epigastric artery.
2-The inferior epigastric artery, is a branch
of the external iliac artery just above the
inguinal ligament. It runs upward &
medially along the medial side of the deep
inguinal ring.
It pierces the fascia transversalis to enter
the rectus sheath anterior to the arcuate
line. It ascends behind the rectus muscle,
supplying the lower central part of the
anterior abdominal wall & anastomoses
with the superior epigastric artery.
3- The deep circumflex iliac artery, is a
branch of the external iliac artery just
above the inguinal ligament. It runs
upward & laterally toward the
anterior superior iliac spine and then
continues along the iliac crest. It
supplies the lower lateral part of the
abdominal wall.
4- The lower 2 posterior intercostal
arteries, are branches of the
descending thoracic aorta,
5- The 4 lumbar arteries, are branches of
the abdominal aorta. They pass
forward between the muscle layers and
supply the lateral part of the
abdominal wall.
N.B. The Umbilicus is a consolidated scar
representing the site of attachment of the
umbilical cord in the fetus. It is situated
in the linea alba slight below it.
Veins of the Anterior Abdominal wall
Superficial Veins
They form a network that radiates out from the
umbilicus.
Above, the network is drained into the axillary
vein via the lateral thoracic vein .
Below, the network is drained into the femoral
vein via the superficial epigastric & great
saphenous veins.
A few small veins , the paraumbilical veins
connect the network through the umbilicus &
along the ligamentum teres to the portal vein.
This forms an important portal – systemic
venous anastomosis.
Deep veins
They are the superior epigastric, inferior
epigastric and deep circumflex iliac veins. They
drains into the internal thoracic & external iliac
veins.
The posterior intercostal veins drain into the
azygos veins. The lumbar veins drain into
inferior vena cava.
Lymph Drainage of the Anterior Abdominal Wall
The skin above the level of the umbilicus is drained upward to the anterior axillary
( pectoral ) group of nodes which can be palpated just beneath the lower border of
the pectoralis major muscle.
Below the level of the umbilicus, the lymph drains downward & laterally to the
superficial inguinal nodes.
The lymph of the skin of the back above the level of the iliac crests drains upward to
the posterior axillary nodes which are palpated on the posterior wall of the axilla.
Below the level of the iliac crests, they drain downward to the superficial inguinal ns
Deep Lymph Vessels
They drain into the internal thoracic, external iliac, posterior mediastinal and paraaortic.
Clinical Notes
1- Umbilical Herniae
A- Congenital hernia ( exomphalos) or omphalocele:
It is caused by a failure of part of the midgut to
return to the abdominal cavity from the
extraembryonic coleom during fetal life.
B- Acquired infantile hernia
it is caused by a weakness in the scar of the
umbilicus in the linea alba. Most disappear as the
abdominal cavity enlarges without treatment.
C- Acquired umbilical of adults (paraumbilical hernia)
The hernial sac protrudes through the linea alba in the
region of the umbilicus. It gradually increase in size and
hang downward. The neck of the sac may be narrow
but the body of the sac contains coils of small and
large intestine and omentum. It is more common in
female than male
2- Incisional Hernia
c
c
A- It is caused to cut one of the segmental nerves
supplying the muscles of the anterior abdominal wall.
Infection with death( necrosis) of the abdominal
musculature. The neck of the sac is large and
adhesion & strangulation of its contents are rare.
B-
Clinical notes
3- Epigastric Hernia
It occurs through the widest part of the linea
alba, any where between the xiphoid process &
umbilicus. It starts off as a small protrusion of
the extraperitoneal fat between the fibers of the
linea alba. Then fat is forced through the linea
alba and trags behind it a small peritoneal sac.
The body of the sac contains a small piece of
greater omentum.
4- Separation of the recti abdominis
It occurs in elderly multiparous women with
weak abdominal muscles. The aponeuroses
forming the rectus sheath become
stretched. The hernial sac, containing
abdominal viscera bulges forward
between the medial margins of the recti
during cough or strains. This can be
corrected by wearing a suitable
abdominal belt.
5- Hernia of the Linea Semilunaris
( SPIGELIAN Hernia )
It is uncommon. It occurs through the
aponeurosis of the transversus
abdominis just lateral to the edge of the
rectus sheath. It occurs just below the
level of the umbilicus. The neck of the
sac is narrow, so that the adhesion and
strangulation of its contents are common
complications.
6- Lumbar Hernia
It occurs through the lumbar triangle
( Petit’s triangle ) and is rare. It is bounded
anteriorly by the posterior margin of the
external obligue muscle and posteriorly
by the anterior border of latissimus dorsi
muscle and inferiorly by the iliac crest. The
floor is formed by the internal oblique and
transversus abdominis muscles. The neck
of the hernia is large and the incidence of
strangulation low.
Dermatomes over:
the xiphoid process T7
the umbilicus T10
the pubis L1
Anterior Abdominal Nerve Block
Area of Anesthesia : The skin of the anterior abdominal wall.
Indications
: Repair of laceration of the anterior abdominal wall ---- Procedure : see figure 4- 16.
Abdominal Pain – Muscle Rigidity and Referred Pain
The rigidity of the muscles may be due to inflammation of the parietal peritoneum
or due to physician’s hand is cold. The patient lies supine and rest the arms by the
sides and draw up the knees to flex the hip joints.