Anatomy

Abdominal anatomy – body Wall

Abdominal anatomy

Anterolateral Abdominal Wall

  • Fascial layers (Table 4-2-1)
    • Superficial fascia: two layers in abdomen
    • Fatty superficial layer (Camper’s fascia)
    • Deeper membranous layer (Scarper’s fascia)
    • Deep fascia—a very thin layer investing the most superficial muscles.
    • Transversalis fascia (endoabdominal fascia)
      • A thin 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 (Table 4-2-1 and Table 4-2-2)
    • 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 that anterolateral abdominal wall
    • Three flat muscles
    • A single vertical muscle.
    • Three flat muscles (Table 4-2-2) include
      • The external abdominal oblique
        1. Largest and most superficial
        2. Fibers run inferiorly and medially and end in aponeurosis that contributes to the rectus sheath.
        3. Inferior border of its aponeurosis forms the inguinal ligament, where it thickens and folds back on itself
        4. Innervated segmentally by T6–T12 spinal nerves and subcostal nerve
      • The internal abdominal oblique
        1. A thin muscular layer
        2. Fibers run inferiorly and laterally and end in an aponeurosis that contributes to the rectus sheath
        3. Inferior aponeurotic fibers join with those of the rectus abdominis to form the conjoint tendon, inserting onto the pubic crest
        4. Innervated segmentally by the ventral rami of T6–T12 spinal nerves
      • The transversus abdominis
        1. Innermost of the three flat muscles
        2. Fibers run transversely and medially and end in an aponeurosis that contributes to the rectus sheath.
        3. Innervated segmentally by the ventral rami of T6–T12 spinal nerves
      • Linea alba
        1. Tendinous raphe running vertically in the midline
        2. Formed by the union of the aponeuroses of the flat muscles on either side
        3. Largely avascular
        4. Umbilicus found in midline
    • Vertical muscle = rectus abdominis (Table 4-2-2)
      • Paired
      • Separated by the linea alba in the midline
      • Wider superiorly than inferiorly
      • Typically composed of four segments connected by tendinous intersections that attach anteriorly to the sheath of this muscle
      • Innervated segmentally by the ventral rami of T6–T12 spinal nerves
      • Have the superior epigastric and the inferior epigastric arteries running inferiorly and superiorly, respectively, on their deep surfaces.
    • Pyramidalis muscle
      • Small, insignificant, triangular muscles arising from the body of the pubis inferiorly
      • Inserts into the linea alba medially
      • Absent in 20% of people
  • Rectus sheath 
    • A tough, 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 primary rami 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 approximately three fourths of the way down 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 supply the rectus muscle.
  • 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 transversely oriented and segmental
    • Nerves
      • Thoracoabdominal nerves
      • Anterior cutaneous branches of the ventral primary rami of T7–T11
        1. T7–T9 supply skin above the umbilicus
        2. T10 supplies skin around the umbilicus
        3. T11 (plus subcostal and ilioinguinal and iliohypogastric nerves) supplies skin below umbilicus
        4. Subcostal nerves (T12) supply skin below umbilicus
        5. Iliohypogastric and ilioinguinal nerves (terminal branches of L1) supplies skin below umbilicus
  • Vascular supply  (Plate 256)
    • Arteries
      • Anterior and collateral branches of posterior intercostal arteries
      • Branches of the internal thoracic arteries
        1. Superior epigastric
        2. Musculophrenic
      • Inferior epigastric (from external iliac)
      • Branches of the femoral artery
        1. Superficial epigastric
        2. Superficial circumflex iliac
    • Veins
      • Venous drainage is via venae comitantes (veins corresponding to) the arteries listed
      • Blood drains away from the umbilicus
      • Venous drainage to the caval system
    • Lymphatics
      • Superficial lymphatics above the umbilicus lymph drains to the axillary nodes
      • Superficial lymphatics below the umbilicus drain to the superficial inguinal nodes
      • Deep lymphatics
        1. Accompany deep veins
        2. Drain to external iliac, common iliac, and lumbar nodes
Abdominal anatomy – body Wall

Plate 256 – abdominal anatomy – Veins of Anterior Abdominal Wall

Posterior abdominal wall

  • Fascia
    • Superficial fascia: single layer
    • Deep fascia—a very thin 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 superiorly to form the medial arcuate ligament—a site of origin of the muscle of the diaphragm
    • Fascia of quadratus lumborum
      • Fuses medially with psoas fascia
      • Thickened superiorly to 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 laterally with deep fascia of internal oblique and transversus abdominus muscles
  • Muscles (Table 4-2-3)
    • 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 laterally extends vertebral column
  • Arteries of the posterior abdominal wall 
    • Abdominal aorta
      • Origin of most of arteries supplying the posterior wall
      • Begins anterior to the body of T12 and ends at bifurcation 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
        1. Gives off inferior epigastric and deep circumflex arteries
        2. Exiting under the inguinal ligament as the femoral artery
        3. Supplies lower limb
      • Internal iliac artery supplies 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)
      • Inferior phrenic arteries
      • Lumbar arteries (four pairs)
    • Unpaired parietal branch: Median sacral artery arising just above aortic bifurcation
  • Veins of the posterior abdominal wall  (Section 4-6: AbdomenVisceral Vasculature)
    • Inferior vena cava (IVC)
      • Formed from union of common iliac veins
      • Begins anterior to body of L5 and passes through the diaphragm at T8.
      • Its tributaries follow branches of aorta
      • Exceptions:
        1. Left gonadal vein drains to left renal vein
        2. 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 anastomoses 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: AbdomenInnervation)
    • Somatic nerves
      • Subcostal nerves
        1. Ventral primary rami of T12
        2. Arise in the thorax
        3. Run inferiorly on surface of quadratus lumborum
        4. Supply external abdominal oblique and skin of anterolateral abdominal wall
      • Lumbar nerves
        1. Dorsal and ventral primary rami of lumbar spinal nerves
        2. Dorsal rami supply muscles and skin of back
        3. Ventral rami pass into substance of psoas major muscle and form lumbar plexus
    • Nerves of lumbar plexus
      • Ilioinguinal and iliohypogastric nerves (L1)
        1. Enter abdomen posterior to medial arcuate ligament
        2. Pierce transverse abdominus near anterior superior iliac spine (ASIS)
        3. Supply skin of suprapubic and inguinal regions
      • Genitofemoral nerve (L1/2)
        1. Emerges from anterior surface of psoas muscle
        2. Runs inferiorly deep to fascia
        3. Divides into genital and femoral branches
      • Lateral femoral cutaneous nerve (L2/3)
        1. Emerges from lateral aspect of psoas muscle
        2. Runs inferiorly on iliacus
        3. Enters thigh posterior to inguinal ligament and medial to ASIS
      • Obturator nerve (L2–L4)
        1. Emerges from medial border of psoas
        2. Descends through pelvis to obturator canal
        3. Supplies muscles and skin of medial thigh
      • Femoral nerve (L2–L4)
        1. Emerges from lateral border of psoas
        2. Innervates iliacus
        3. Passes beneath inguinal ligament on surface of iliopsoas muscle
        4. Innervates muscles of anterior thigh
      • Lumbosacral trunk (L4/5)
        1. Descend over ala of sacrum into pelvis
        2. Joins in formation of sacral plexus
    • Autonomic nerves
      • Thoracic splanchnic nerves
        1. Greater (T5–T9), lesser (T10–T11) and least (T12) thoracic splanchnic nerves
        2. Convey presynaptic sympathetic fibers to celiac, superior mesenteric, and aorticorenal sympathetic ganglia
      • Lumbar splanchnic nerves
        1. Rise of abdominal sympathetic trunks
        2. Three to four in number
        3. Convey presynaptic sympathetic fibers to inferior mesenteric, intermesenteric, and superior hypogastric plexuses
      • Prevertebral sympathetic ganglia
        1. Celiac
        2. Superior mesenteric
        3. Inferior mesenteric
        4. Aorticorenal
      • Parasympathetic fibers
        1. Preganglionic
        2. From anterior and posterior vagal trunks and pelvic splanchnic nerves
      • Autonomic plexuses
        1. Contain preganglionic sympathetic and parasympathetic fibers, postganglionic sympathetic fibers, sympathetic ganglia ((prevertebral), and visceral afferent fibers
        2. Some named for major blood vessels (periarterial): celiac, superior mesenteric, inferior mesenteric, intermesenteric, aorticorenal
        3. Superior hypogastric plexus—continuous with inferior mesenteric and intermesenteric plexuses at aortic bifurcation

Internal features of anterior abdominal wall

  • Lined by parietal 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
    • A sharp-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)

Hesselbach’s (inguinal) triangle

  • Boundaries:
    • Medially: lateral border of rectus abdominis
    • Laterally: inferior epigastric vessels
    • Inferiorly: inguinal ligament
  • Significance
    • Only peritoneum, endoabdominal fascia and transversalis fascia form the wall
    • The superficial inguinal ring lies directly external 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 260)

  • Oblique canal, approximately 4 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 medially by the lacunar ligament
  • Contents:
    • Spermatic cord in men
    • Round ligament in women (Section 5: Pelvis and Perineum)
    • Ilioinguinal nerve
    • Blood and lymphatic vessels
Abdominal anatomy – body Wall

Plate 260 : abdominal anatomy – Inguinal Canal and Spermatic Cord

Abdominal anatomy – body Wall

Plate 261 : abdominal wall – Indirect Inguinal Hernia

Common Surgical Scars (Table 4-2-4)