Anatomy of the Abdominal Wall Part I

Structure of the Anterior Abdominal Wall

• Composed of skin, superficial fascia, deep fascia, muscles, extraperitoneal fascia, and parietal peritoneum.
• Skin attachment is loose except at the umbilicus, where it connects to scar tissue.
• Umbilicus signifies the site of umbilical cord attachment in the fetus.

Nerve Supply

• Cutaneous innervation from lower six thoracic nerves and the 1st lumbar nerve.
• Key dermatomes:
  • T7: Epigastrium near xiphoid process
  • T10: Umbilicus
  • L1: Area just above inguinal ligament and symphysis pubis

Blood Supply

• Arteries:
  • Midline skin supplied by superior and inferior epigastric arteries.
  • Flank skin supplied by intercostal, lumbar, and deep circumflex iliac arteries.
  • Inguinal region skin supplied by superficial epigastric, superficial circumflex iliac, and superficial external pudendal arteries.
• Veins:
  • Above umbilicus drains into axillary vein via lateral thoracic vein.
  • Below umbilicus drains into femoral vein via superficial epigastric and great saphenous veins.

Fascia

• Superficial Fascia:
  • Fatty layer (Camper's fascia) varies in thickness, especially in obese individuals.
  • Membranous layer (Scarpa's fascia) fuses with deep fascia below inguinal ligament, forming a sheath for genital structures.
• Deep Fascia:
  • Thin connective tissue layer covering abdominal muscles, lies just beneath the membranous layer.

Muscles of the Anterior Abdominal Wall

• External Oblique Muscle (EOM):

  • Largest and most superficial abdominal muscle.
  • Fibers run diagonally downward and medially from lower 8th rib to xiphoid process, linea alba, pubic crest, and iliac crest.
  • Forms superficial inguinal ring and external spermatic fascia.

• Internal Oblique Muscle (IOM):

  • Located deep to EOM with fibers running perpendicular to EOM.
  • Originates from lumbar fascia, iliac crest, and inguinal ligaments, inserting into lower three rib cartilages, xiphoid process, linea alba, and pubis.
  • Conjoint tendon formed from IOM and transversus abdominis aponeurosis is crucial in the inguinal region.

• Transversus Abdominis (TA):

  • Positioned deep to IOM with horizontal fiber orientation.
  • Originates from costal cartilages, lumbar fascia, iliac crest, and inguinal ligament, with insertions similar to IOM.
  • Integrates into the conjoint tendon, anchored to pubic crest and pectineal line.

• Rectus Abdominis (RA):

  • Long, strap-like paired muscle divided by linea alba, enclosed within a fibrous sheath from surrounding aponeuroses.