25 Body Wall

STUDYAIMS

At the end of your study, you should be able to:

Know the layers of the anterior abdominal wall from superficial to deep

Understand the orientation and functions of the muscles of the anterolateral abdominal wall

Describe the structure of the rectus sheath and its contents

Describe the neurovascular supplyof the abdominal wall

Understand the boundaries of the inguinal canal and layers of the spermatic cord

Describe the boundaries of Hesselbach's triangle

Know the etiologyand location of the umbilical peritoneal folds

Understand the structure and organization of the posterior abdominal wall and its neurovascular relations

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GUIDE

Abdomen: Body Wall

[Plate 324, Abdominal Scans: Axial CT Images]

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[Plate 330, Schematic Cross Section of Abdomen at L3, 4]

Anterolateral Abdominal Wall

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Fascial layers

Superficial fascia: two layers in abdomen

Fattysuperficial layer (Camper's fascia)

Deeper membranous layer (Scarper's fascia)

Deep fascia-a verythin layer investing the most superficial muscles.

Transversalis fascia (endoabdominal fascia)

Athin membranous sheet lining most of the abdominal wall

Lies deep to the transversus muscles and the linea alba

Endoabdominal fat separates the transversalis fascia from the parietal peritoneum Muscles

Functions

Protect the viscera

Help maintain posture

Can compress the abdominal contents, thus raising intra-abdominal pressure, such as in sneezing, coughing, defecating, micturating, lifting, and childbirth

Four paired muscles make up the anterolateral abdominal wall

Three flat muscles

Asingle vertical muscle.

Three flat muscles include

The external abdominal oblique

a.Largest and most superficial

b.Fibers run inferiorlyand mediallyand end in aponeurosis that contributes to the rectus sheath.

c.Inferior border of its aponeurosis forms the inguinal ligament, where it thickens and folds back on itself

d.Innervated segmentallybyT6-T12 spinal nerves and subcostal nerve

The internal abdominal oblique

a.Athin muscular layer

b.Fibers run inferiorlyand laterallyand end in an aponeurosis that contributes to the rectus sheath

c.Inferior aponeurotic fibers join with those of the rectus abdominis to form the conjoint tendon, inserting onto the pubic crest

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d. Innervated segmentallybythe ventral rami of T6-T12 spinal nerves The transversus abdominis

a.Innermost of the three flat muscles

b.Fibers run transverselyand mediallyand end in an aponeurosis that contributes to the rectus sheath.

c.Innervated segmentallybythe ventral rami of T6-T12 spinal nerves

Linea alba

a.Tendinous raphe running verticallyin the midline

b.Formed bythe union of the aponeuroses of the flat muscles on either side

c.Largelyavascular

d.Umbilicus found in midline

Vertical muscle = rectus abdominis

Paired

Separated bythe linea alba in the midline

Wider superiorlythan inferiorly

Typicallycomposed of four segments connected bytendinous intersections that attach anteriorlyto the sheath of this muscle

Innervated segmentallybythe ventral rami of T6-T12 spinal nerves

Have the superior epigastric and the inferior epigastric arteries running inferiorlyand superiorly, respectively, on their deep surfaces.

Pyramidalis muscle

Small, insignificant, triangular muscles arising from the bodyof the pubis inferiorly

Inserts into the linea alba medially

Absent in 20% of people Rectus sheath

Atough, fibrous sheath composed of the aponeuroses of the three flat muscles

Extends from the xiphoid process and fifth through seventh costal cartilages to pubic symphysis and crests

Contains the superior and inferior epigastric vessels, lymphatics and branches of the ventral primaryrami of T7-T12

Encloses the rectus abdominis and the pyramidalis muscle

Semilunar line marks lateral border

Has a crescent-shaped line-the arcuate line-on its posterior wall approximatelythree fourths of the waydown the wall

Above the arcuate line:

Anterior wall composed of the aponeurosis of the external abdominal oblique and the anterior layer of the aponeurosis of the internal abdominal oblique

Posterior wall composed of the posterior layer of the aponeurosis of the internal abdominal oblique, the aponeurosis of the transversus abdominis, the transversalis fascia of the abdomen, and parietal peritoneum

Below arcuate line

Aponeuroses of all three flat muscles pass anterior to the rectus muscle, reinforcing the anterior wall

Posterior wall composed of just transversalis fascia and parietal peritoneum

Has vessels and nerves entering the sheath at its lateral edge, the semilunar line, to supplythe rectus muscle.

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Nerve supply

Neurovascular plane

Found between the internal abdominal oblique and the transversus abdominis

Contains the vessels and nerves supplying the skin and muscles of the anterior and lateral abdominal wall.

Nerves and vessels are transverselyoriented and segmental

Nerves

Thoracoabdominal nerves

Anterior cutaneous branches of the ventral primaryrami of T7-T11

a.T7-T9 supplyskin above the umbilicus

b.T10 supplies skin around the umbilicus

c.T11 (plus subcostal and ilioinguinal and iliohypogastric nerves) supplies skin below umbilicus

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d.Subcostal nerves (T12) supplyskin below umbilicus

e.Iliohypogastric and ilioinguinal nerves (terminal branches of L1) supplies skin below umbilicus

Vascular supply

Arteries

Anterior and collateral branches of posterior intercostal arteries

Branches of the internal thoracic arteries

a.Superior epigastric

b.Musculophrenic

Inferior epigastric (from external iliac)

Branches of the femoral artery

a.Superficial epigastric

b.Superficial circumflexiliac

Veins

Venous drainage is via venae comitantes (veins corresponding to the arteries listed)

Blood drains awayfrom the umbilicus

Venous drainage to the caval system

Lymphatics

Superficial lymphatics above the umbilicus lymph drains to the axillarynodes

Superficial lymphatics below the umbilicus drain to the superficial inguinal nodes

Deep lymphatics

a.Accompanydeep veins

b.Drain to external iliac, common iliac, and lumbar nodes

Posterior abdominal wall

[Plate 258, Veins of Posterior Abdominal Wall]

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Fascia

Superficial fascia: single layer

Deep fascia-a verythin layer investing the most superficial muscles.

Transversalis fascia (endoabdominal fascia)

Endoabdominal fat separates the transversalis fascia from the parietal peritoneum

Psoas sheath

Fascia covering the psoas muscle

Attaches to lumbar vertebrae and pelvic brim

Thickened superiorlyto form the medial arcuate ligament-a site of origin of the muscle of the diaphragm

Fascia of quadratus lumborum

Fuses mediallywith psoas fascia

Thickened superiorlyto form the lateral arcuate ligament-a site of origin of the muscle of the diaphragm

Thoracolumbar fascia (Section 2: Back and Spinal Cord)

Composed of anterior and posterior layers

Encloses the deep muscles of the back

Thick and strong in the lumbar region

Extends from 12th rib to iliac crest and continuous laterallywith deep fascia of internal oblique and transversus abdominus muscles

Muscles

Psoas major

Long and thick

Lies lateral, and is attached to, the lumbar vertebrae

Tendon passes deep to inguinal ligament to lesser trochanter of femur

Together with iliacus forms iliopsoas muscle, which flexes the hip, helps maintain erect posture

Lumbar plexus of nerves embedded within it

Iliacus

Attaches to superior two thirds of iliac fossa

Joins psoas to form iliopsoas

Quadratus lumborum

Thick quadrangular muscle of posterior wall

Extends from 12th rib and tips of lumbar transverse processes to iliac crest Flexes and laterallyextends vertebral column

Arteries of the posterior abdominal wall (Section 4-6: Abdomen-Visceral Vasculature)

Abdominal aorta

Origin of most of arteries supplying the posterior wall

Begins anterior to the bodyof T12 and ends at bifurcation of the common iliac arteries at L4

Common iliac artery

Follows the medial border of the psoas

Divides into internal and external iliac arteries at pelvic brim

External iliac

a.Gives off inferior epigastric and deep circumflexarteries

b.Exits under the inguinal ligament as the femoral artery

c.Supplies lower limb

Internal iliac arterysupplies pelvis

Unpaired visceral branches of abdominal aorta

Celiac trunk (T12)

Superior mesenteric (L1)

Inferior mesenteric (L3)

Paired visceral branches

Suprarenal arteries (L1)

Renal arteries (L1)

Gonadal arteries (L2) (Note: gonadal arteries branch from the anterior aorta)

Paired parietal branches

Subcostal arteries (T12)

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Inferior phrenic arteries

Lumbar arteries (four pairs)

Unpaired parietal branch: Median sacral arteryarising just above aortic bifurcation

Veins of the posterior abdominal wall (Section 4-6: Abdomen-Visceral Vasculature)

Inferior vena cava (IVC)

Formed from union of common iliac veins

Begins anterior to bodyof L5 and passes through the diaphragm at T8.

Its tributaries follow branches of aorta

Exceptions:

a.Left gonadal vein drains to left renal vein

b.Left suprarenal vein drains to left renal vein

Blood from abdominal viscera

Drains via portal system and liver

Reaches IVC through the hepatic veins

Ascending lumbar veins

Drain to azygos/hemiazygos veins and thence to superior vena cava (SVC)

Forms an anastomosis between IVC and SVC.

Lymphatics of the posterior abdomen

Common iliac nodes

Receive lymph from the external and internal iliac nodes

Drain to lumbar (para-aortic) nodes

Lumbar (para-aortic) nodes

Receive lymph from the posterior abdominal wall, descending colon, kidneys, ureters, testes/ovaries, uterus, uterine tubes

Efferent vessels form the lumbar lymphatic trunks

Preaortic nodes

Receive lymph from the digestive tract, liver, spleen, and pancreas

Efferent vessels form the intestinal lymphatic trunks

Nerves of the posterior abdominal wall (Section 4-7: Abdomen-Innervation)

Somatic nerves Subcostal nerves

a.Ventral primaryrami of T12

b.Arise in the thorax

c.Run inferiorlyon surface of quadratus lumborum

d.Supplyexternal abdominal oblique and skin of anterolateral abdominal wall

Lumbar nerves

a.Dorsal and ventral primaryrami of lumbar spinal nerves

b.Dorsal rami supplymuscles and skin of back

c.Ventral rami pass into substance of psoas major muscle and form lumbar plexus

Nerves of lumbar plexus

Ilioinguinal and iliohypogastric nerves (L1)

a.Enter abdomen posterior to medial arcuate ligament

b.Pierce transverse abdominus near anterior superior iliac spine (ASIS)

c.Supplyskin of suprapubic and inguinal regions

Genitofemoral nerve (L1/2)

a.Emerges from anterior surface of psoas muscle

b.Runs inferiorlydeep to fascia

c.Divides into genital and femoral branches

Lateral femoral cutaneous nerve (L2/3)

a.Emerges from lateral aspect of psoas muscle

b.Runs inferiorlyon iliacus

c. Enters thigh posterior to inguinal ligament and medial toASIS Obturator nerve (L2-L4)

a.Emerges from medial border of psoas

b.Descends through pelvis to obturator canal

c.Supplies muscles and skin of medial thigh

Femoral nerve (L2-L4)

a.Emerges from lateral border of psoas

b.Innervates iliacus

c.Passes beneath inguinal ligament on surface of iliopsoas muscle

d.Innervates muscles of anterior thigh

Lumbosacral trunk (L4/5)

a.Descends over ala of sacrum into pelvis

b.Joins in formation of sacral plexus

Autonomic nerves

Thoracic splanchnic nerves

a.Greater (T5-T9), lesser (T10-T11) and least (T12) thoracic splanchnic nerves

b.Conveypresynaptic sympathetic fibers to celiac, superior mesenteric, and aorticorenal sympathetic ganglia

Lumbar splanchnic nerves

a.Rise of abdominal sympathetic trunks

b.Three to four in number

c.Conveypresynaptic sympathetic fibers to inferior mesenteric, intermesenteric, and superior hypogastric plexuses

Prevertebral sympathetic ganglia

a.Celiac

b.Superior mesenteric

c.Inferior mesenteric

d.Aorticorenal

Parasympathetic fibers

a.Preganglionic

b.From anterior and posterior vagal trunks and pelvic splanchnic nerves

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Autonomic plexuses

a.Contain preganglionic sympathetic and parasympathetic fibers, postganglionic sympathetic fibers, sympathetic ganglia (prevertebral), and visceral afferent fibers

b.Some named for major blood vessels (periarterial): celiac, superior mesenteric, inferior mesenteric, intermesenteric, aorticorenal

c.Superior hypogastric plexus-continuous with inferior mesenteric and intermesenteric plexuses at aortic bifurcation

Internal features of anterior abdominal wall

[Plate 250, Veins of Anterior Abdominal Wall]

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Lined byparietal peritoneum

Has five peritoneal folds, inferior to the umbilicus

Median umbilical fold

Extends in the midline from the bladder to the umbilicus

Represents the remnant of the urachus

Medial umbilical folds (two)

One on either side of median umbilical fold

Represent remnants of umbilical arteries

Lateral umbilical folds (two)

One on either lateral side of the medial umbilical folds

Over the inferior epigastric vessels

Peritoneal fossae are formed between the umbilical folds:

Supravesical fossae: between the median and medial folds

Medial inguinal fossae: between the medial and lateral folds

Lateral inguinal fossae:

Lateral to lateral folds

Site of deep inguinal ring (beneath peritoneum)

Falciform ligament

Asharp-edged fold of peritoneum

Extends between peritoneum of the abdominal wall above the umbilicus and the liver

Contains the round ligament of the liver (ligamentum teres hepatis: remnant of the umbilical vein)

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Hesselbach's (inguinal) triangle

Boundaries:

Medially: lateral border of rectus abdominis

Laterally: inferior epigastric vessels

Inferiorly: inguinal ligament

Significance

Onlyperitoneum, endoabdominal fascia and transversalis fascia form the wall

The superficial inguinal ring lies directlyexternal to it

It is thus the site where direct inguinal hernias protrude from the abdominal cavity

Inguinal canal: A feature of the anterior abdominal wall

[Plate 253, Inguinal Region: Dissections]

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[Plate 254, Inguinal Canal and Spermatic Cord]

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[Plate 255, Femoral Sheath and Inguinal Canal]

Oblique canal, approximately4 cm long at the inferior margin of the anterior abdominal wall Parallel and superior to the medial half of the inguinal ligament

Deep inguinal ring: internal entrance to canal

Entrance to the canal through the transversalis fascia.

Located 1.25 cm superior to the midpoint of the inguinal ligament

Occurs lateral to the epigastric vessels Superficial ring: external exit of the canal

Exit through the external oblique aponeurosis

Located superolateral to the pubic tubercle Boundaries:

Anterior wall: external oblique aponeurosis (and internal oblique laterally)

Posterior wall

Transversalis fascia laterally

Internal oblique and conjoint tendon (joint insertion of aponeuroses of internal oblique and transverses abdominus) medially

Roof: arching fibers of internal oblique

Floor: inguinal ligament, reinforced mediallybythe lacunar ligament Contents:

Spermatic cord in men

Round ligament in women (Section 5: Pelvis and Perineum)

Ilioinguinal nerve

Blood and lymphatic vessels

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