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TOPOGRAPHIC ANATOMY OF THE ANTERIOR
ABDOMINAL WALL, OF THEÂ INGUINAL CANAL, OF THE
FEMORAL CANAL.
OPERATIONS IN HERNIAS.
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The boundaries of the anterior abdominal wall are:
superiorly – Âthe costal arches and xiphoid process,
inferiorly – the iliac crests, inguinal folds (projection of the inguinal ligaments), pubic
tuÂbercles and the superior margin of the symphysis pubis,
laterally – the vertical line, which connects the end of the 11 rib with the iliac crests
(Lesgaft's line). This line is the continuation of the midaxillary line, and it separates the abdominal
region from the lumbar region.
The surface landmarks are the following: xiphoid process, costal margin, iliac crest, pubic
tubercle, symphysis pubis, inÂguinal ligament, superficial inguinal ring, linea alba, umbiliÂcus,
rectus abdominis muscle.
The anterior abdominal wall can be divided by horizontal and vertical planes (lines) into a
number of regions which are of use to the clinician when describing the site of pain felt by a patient
or of abnormal physical sings such as areas of tenderness or tumors. Two transverse and two
vertical planes (lines) divide the anterior abdominal wall into three midÂline, three left, and three
right regions. The vertical right and left lateral planes almost correspond to the midclavicular
planes of the thorax and pass through the midpoint of a line joining the anterior superior iliac spine
and the symphysis pubis (the midinÂguinal point).
The subcostal plane joins the lowest point of the costal margin on each side, that is the
tenth costal cartilage. The subÂcostal plane lies at the level of the third lumbar vertebra. The
interspinal plane (linea bispinalis) joins the anterior superior iliac spine on each side. The midline
regions are called the epiÂgastric, umbilical, and hypogastric regions. The lateral regions are
called the hypochondriac, the lateral and inguinal (iliac) regions.
Structures of the abdominal wall.
Skin. The natural lines of cleavage in the skin are constant and run almost horizontally
around the trunk. This is important cliÂnically, since an incision along a cleavage line will heal as
a narrow scar, whereas one that crosses the lines will heal as a wide or heaped-up scar. The skin is
supplied by the cutaneous branches of the seventh to twelfth intercostal nerves and by the first
lumbar nerve in the form of the iliohypogastric nerve. A pleurisy involving the lower costal parietal
pleura will cause pain in the overlying skin that may radiate down into the abdoÂmen.
Although it is unlikely to cause rigidity of the abdominal muscles, it may cause confusion
in making a diagnosis unless theÂse anatomical facts are remembered.
Beneath the skin is located the subcutaneous tissue. The layer of adipose tissue is very
vaÂriable thickness. Cutaneous arteries, which are branches of the superior and inferior epigastric
arteries, supply the area near the midline, and branches from the intercostal, lumbar, and deep
circumflex iliac arteries supply the flanks. .
The venous blood is collected into a network of veins that radiates out from the umbilicus
(thoracoepigastric, intercostal, and superficial epigastric veins). The network is drained above
into the axillary vein via the lateral thoracic vein and below into the femoral vein via the superficial
epigastric and great saphenous veins. A few small veins, the paraumbilical veins, conÂnect the
network through the umbilicus and along the teres ligament to the portal vein. They form an
important portal-systemic venous anastomosis.
The superficial veins around the umbilicus and the paraumbiÂlical veins connecting them
to the portal vein may become grossly distended in cases of portal vein obstruction. The distended
subÂcutaneous veins radiate out from the umbilicus, producing the clinical picture referred to as
caput Medusae. If there is obsÂtruction in the superior vena or inferior vena cava, the venous
blood causes distention of the veins running from the anterior chest wall to the thigh.
The superficial fascia is divided into a superficial and deÂep layer. The superficial layer
of the superficial fascia is conÂtinuous with a superficial fascia of the thigh. The deep layer of the
superficial fascia (Tomson's plate) or membranous layer is attached to the inguinal ligament and
form similar layer in the perineum. It is important clinically, since beneath it the is a potential
closed space that does not open into the thigh, but is continuous with the superficial perieneal
pouch via the penis and scrotum. Rupture of the penile urethra may be followed by extraÂvasation
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 the superficial fascia. The urine is excluded from
the thigh because of the attachment of the Tomson's plate to the inguinal ligament.
In the anterior abdominal wall the proper or deep fascia is merely a thin layer covering
the muscles.
THE MUSCLES OF THE ANTERIOR ABDOMINAL WALL
The musculature of the anterior and lateral walls of the abÂdomen is made up of a
trilaminar sheet on either side of a pair of vertically oriented muscles. The thin aponeurotic tendons
of the three lateral muscles form a sheath around each vertical muscle before fusing in the midline
at the linea alba. The trilaÂminar sheet is composed of:
1.     The external oblique muscle.
2.     The internal oblique muscle.
3.     The transversus abdominis muscle.
The vertically oriented muscles are the rectus abdominis muscles. In the lower part of the
rectus sheath there may be preÂsent a small muscle called the pyramidalis. The cremaster muscle,
which is derived from the lower fibers of the internal oblique, passes inferiorly as a covering of
the spermatic cord and the scrotum.
The external oblique muscle arises as digitations from the outer surfaces of the lower
eight ribs. The fleshy fibers fan out downward and medially over the anterior abdominal wall.
There is a free posterior margin to the muscle where its most posterior fibers run from the twelfth
rib to the anterior half of the outer margin of the iliac crest. The remaining more obliquely running
fibers become an aponeurotic sheet which contributes to the anteÂrior sheath of the rectus muscle
before fusing with its fellow at the linea alba in the midline.
The lower free margin of the aponeurosis extends from the anÂterior superior iliac spine
to the pubic tubercle and is called the inguinal ligament. From the medial end of the ligament the
lacunar ligament extends backward and upward to the pectineal liÂne on the superior ramus of the
pubis. Its sharp, free crescentic edge 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. To the inferior rounded border of the inguinal ligament is attached the deep
fascia of the thigh – the fascia lata.
A triangular-shaped defect in the external oblique aponeuroÂsis lies immediately above
and medial to the pubic tubercle. This is known as the 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.
The internal oblique muscle arise from the thoracolumbar fascia, the anterior two-thirds
of the iliac crest deep to the attachment of the external oblique, and from the lateral two-thirds of
the inguinal ligament. The fibers fan out from this origin. The uppermost run upward and medially
to become attached to the costal margin. The intermediate fibers become aponeurotic and help in
the formation of the rectus sheath before joining the linea alba. The lowermost are attached by a
flattened tendon to the pectineal line on the superior pubic ramus.
The fibers of transversus abdominis muscle arise from a long origin which extends from
the deep surface of the costal margin, the thoracolumbar fascia, the anterior two-thirds of the
medial margin of the iliac crest, and the outer half of the inguinal ligament. Running approximately
transversely across the abdominal wall, the fibers also become aponeurotic and contribute to the
rectus sheÂath before joining the linea alba. The muscular fibers form the linea semilunaris
(Spigelii) in the passage to the aponeurosis. This line extends from the inguinal ligament to the
sternum.
THE RECTUS ABDOMINIS
The two rectus abdominis muscles form the vertical component of the anterior abdominal
musculature and lie on either side of the linea alba. The muscles are broad superiorly and narrow
infeÂriorly. Each is attached to the fifth, sixth, and seventh costal cartilages above and below by
tendinous and fleshy insertions to the pubic crest and the symphysis pubis. The anterior surface of
the muscle is crossed by three tendinous intersections. One of these lies at the level of the umbilicus
and two are above. These intersections are strongly attached to the anterior wall of the rectus
sheath. The rectus abdominis is enclosed between the apoÂneuroses of the external oblique, the
internal oblique, and the transversus, which form the rectus sheath.
The piramidalis muscle is often absent. It arises by its baÂse from the anterior surface of
the pubis and is inserted into the linea alba. It lies in front of the lower part of the rectus abdominis.
THE RECTUS SHEATH
Each rectus abdominis muscle is enclosed in a fibrous sheath formed by the aponeurotic
tendons of the three lateral muscles. The external oblique contributes to the anterior layer the
sheath over its whole extent. Below the costal margin the internal obliÂque aponeurosis splits
around the muscle contributing to anterior and posterior layers and the aponeurosis of the
transversus abdoÂminis passes into the posterior layer.
Midway between the umbilicus and the symphysis pubis, the posterior wall of the sheath
becomes deficient since all aponeuÂroses pass anterior to the rectus abdominis. At the level at
which the aponeuroses of all three lateral muscles fuse to form only the anterior layer of the sheath,
the posterior sheath terÂminates at a free margin called the arcuate line (Douglasi line). It is here
that the inferior epigastric artery enters the sheath to run superiorly on the deep surface of the
rectus abdominis muscle. The artery anastomoses with the superior epigastric arteÂry, which has
entered the sheath from above by passing deep to the costal margin. Below the level of the arcuate
line the rectus abdominis lies on the transverse fascia. The muscles of the anterior abdominal wall
are supplied by the lower six thoracic and first lumbar segmental nerves. The thoracic nerves
emerge beÂneath the costal margin and run downward and forward the abdomiÂnal wall between
the internal oblique and transversus abdominis muscles.
The nerves are accompanied by branches of the musculophrenic or the first lumbar artery.
To thoracic (intercostal) nerves are added the iliohypogastric and ilioinguinal nerves which are
deriÂved from the first lumbar nerve. These supply the lower fibers of the external oblique,
internal oblique, and transversus abdominis muscles. In addition to branches of the
musculophrenic and lumbar arteries, which supply the lateral muscles, the superior and inÂferior
epigastric arteries supply the rectus abdominis muscle.
THE RETROMUSCULAR LAYERS
They include: the fascia transversalis, the extraperitoneal (preperitoneal) fat, the parietal
peritoneum.
The fascia transversalis is a thin layer of fascia that liÂnes the transversus abdominis
muscle and is continuous with a siÂmilar layer lining the diaphragm and the iliacus muscle. It is
important to understand that the fascia transversalis, the diaphÂragmatic fascia, the iliacus fascia,
and the pelvic fascia form one continuous lining to the abdominal and pelvic cavities.
The extraperitoneal fat is a thin layer of connective tissue that contains a variable amount
of fat and lies between the fasÂcia transversalis and the parietal peritoneum.
The walls of the abdomen are lined with parietal peritoneum. This is a thin serous
membrane and is continuous below with the parietal peritoneum lining the pelvis. The parietal
peritoneum lining the anterior abdominal wall is supplied segmentally by inÂtercostal and lumbar
nerves, which also supply the overlying muscles and skin.
The linea alba extends from the xiphoid process down to the symphysis pubis and is formed
by the fusion of the lateral muscÂles of the two sides. Wider above the umbilicus, it narrows down
below the umbilicus to be attached to the symphysis pubis. The linea alba has the through slitlike
spaces. The vessels, nerves and fat (which connects the extraperitonial fat with subcutaneous fat)
pass through this spaces. This slits can be by the places of outlet of the herniae. It is called the
hernia of the linea alba or the epigastric hernia. The linea alba is a weak place of the anterior
abdominal wall.
The umbilicus is located in the middle of the line which connects the apex of the
xiphoid process with the superior margin of the symphysis pubis. The umbilicus is drawn in scar
which is formed in place of the umbilical ring.
The umbilical ring is the foramen which is limited by the aponeurotic fibers of the linea
alba. The urachus, umbilical vein, two umbilical arteries pass through the umbilical ring in the
intrauterine development. Then this structures are turned into the ligaments.
The urachus is turned into the median umbilical ligament.
The umbilical vein is turned into the ligament teres of the liver.
The umbilical arteÂ...
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