Abdominal Wall: Anatomy & Physiology

Abdominal Wall Layers

Layers of Abdominal Wall

  • Skin
  • Camper’s Fascia (Fatty Superficial)
  • Scarpa’s Fascia (Fibrous Deep)
  • Muscle Layers
  • Transversalis Fascia
  • Extraperitoneal (Preperitoneal) Fat
  • Peritoneum

Layers of the Abdominal Wall

Muscle Layers

  • Lateral to Rectus Abdominis
    • External Oblique Muscle (EO)
    • Internal Oblique Muscle (IO)
    • Transversus Abdominis Muscle (TA)
  • Arcuate Line: 2/3 Distance from Umbilicus to Pubic Crest
  • Rectus Abdominis, Above Arcuate Line
    • Anterior Rectus Sheath – Aponeurosis of EO & ½ IO
    • Rectus Abdominis
    • Posterior Rectus Sheath – Aponeurosis of ½ IO & TA
  • Rectus Abdominis, Below Arcuate Line
    • Anterior Rectus Sheath – Aponeurosis of EO, IO & TA
    • Rectus Abdominis

Sensory Nerves

  • Derived from the T7-T11 Intercostal Nerves, T12 Subcostal Nerve & L1 Spinal Nerve
  • Travel Between the Internal Oblique & Transversus Abdominis Muscles

Above the Arcuate Line

Below the Arcuate Line

Groin Structure

Inguinal Rings

  • Deep Inguinal Ring: Transversalis Fascia
  • Superficial Inguinal Ring: Aponeurosis of External Oblique

Spermatic Cord

  • Layers
    • External Spermatic Fascia: Continuous with External Oblique
    • Cremasteric Muscle: Continuous with Internal Oblique
    • Internal Spermatic Fascia: Continuous with Transversalis Fascia
  • Structures: Vas Deferens, Nerves & Testicular Vessels

Inguinal Rings 1

Ligaments

  • Inguinal (Poupart’s) Ligament
    • From Fascia of External Oblique
    • Anterior Superior Iliac Spine (ASIS) to Pubic Tubercle
  • Lacunar Ligament
    • Where Inguinal Ligament Inserts in Pubis
    • Medial Boundary of Femoral Canal
  • Pectineal (Cooper’s) Ligament
    • Extension of Lacunar Ligament Along the Pubic Bone
    • Posterior Border of Femoral Canal
  • Conjoined Tendon
    • Fascia of Internal Oblique & Transversalis Fascia

Groin Ligaments

Regions

  • Hasselbach’s Triangle
    • Site of Direct Hernias
    • Borders:
      • Lateral: Inferior Epigastrics
      • Medial: Rectus Abdominis
      • Inferior: Inguinal Ligament
  • Inguinal Canal
    • Borders:
      • Superior: Conjoint Tendon
      • Inferior: Inguinal Ligament
      • Posterior/Floor: Transversalis Fascia
      • Anterior: External Oblique
  • Femoral Canal
    • Borders:
      • Anterior: Inguinal Ligament
      • Posterior: Cooper’s Ligament
      • Medial: Lacunar Ligament
      • Lateral: Femoral Vein
    • Structures (Lateral to Medial) Mn
      • Nerve, Artery, Vein, Empty Space, Lymphatics, Lacunar Ligament
  • Femoral Triangle
    • Borders:
      • Superior: Inguinal Ligament
      • Medial: Adductor Longus
      • Lateral: Sartorius Muscle

Hasselbach’s Triangle

Femoral Canal 1

Laparoscopic Inguinal Triangles

  • “Mercedes Sign” Transected by the Inguinal Ligament
    • Superior Fork – Epigastric Vessels
    • Inferior/Lateral Fork – Testicular Vessels
    • Inferior/Medial Fork – Vas Deferens
  • Above the Inguinal Ligament:
    • Direct Triangle: Medial to the Epigastric Vessels
    • Indirect Triangle: Lateral to the Epigastric Vessels
  • Below the Inguinal Ligament:
    • Femoral Triangle: Medial to the Vas Deferens
    • Triangle of Doom: Between the Vas Deferens & Testicular Vessels
    • Triangle of Pain: Lateral to the Testicular Vessels

Laparoscopic Danger Triangles

  • Triangle of Doom
    • Inferior to Inguinal Ligament & Lateral
    • Borders: Vas Deferens, Testicular Vessels & Peritoneal Fold
    • Contents: External Iliac Vessels
  • Triangle of Pain
    • Borders: Iliopubic Tract, Testicular Vessels & Peritoneal Fold
    • Contents: Femoral Nerve, Femoral Branch of Genitofemoral Nerve & Lateral Femoral Cutaneous Nerve
  • Avoid Laparoscopic Inferolateral Tacks & Sutures Inferior to Inguinal Ligament & Lateral to Vas Deferens

Laparoscopic Inguinal Triangles 2

Laparoscopic Inguinal Triangles 2

Groin Nerves

Ilioinguinal Nerve

  • Enters Through Superior Border Between Internal Oblique & Transversus Abdominis
    • Near Iliohypogastric Nerve
  • Runs Parallel Over the Spermatic Cord
    • Not Inside
  • Function: Cutaneous Sensation Over Penis Root & Scrotum

Iliohypogastric Nerve

  • Enters Through Superior Border Between Internal Oblique & Transversus Abdominis
    • Near Ilioinguinal Nerve
  • Runs Transverse Over Internal Oblique, Superior to Deep Ring
  • Function: Hypogastric Cutaneous Sensation

Genitofemoral Nerve

  • Genital Branch
    • Travels Through Deep Ring to Cremaster Muscle
    • Function: Cremaster Muscle & Scrotal Skin
  • Femoral Branch
    • Parallels Iliac Vessels Through Femoral Canal
    • Function: Inner Thigh Sensation

Lateral Femoral Cutaneous Nerve

  • Initially Parallels Ilioinguinal and Iliohypogastric Nerves
    • Exits Posterior to Inguinal Ligament Through Femoral Canal
  • Function: Lateral Thigh Sensation

Nerves of the Inguinal Canal

Mnemonics

Order of the Femoral Structures

  • N.A.V.E.L. to the Navel (Lateral to Medial)
    • Nerve > Artery > Vein > Empty Space > Lymphatics/Lacunar Ligament
  • Others:
    • Venous to the Penis – Vein is Medial to Artery
    • “V” to the Vagina – Vein is Medial to Artery

References

  1. Gray H. Anatomy of the Human Body (1918). Public Domain.
  2. Carter J, Duh QY. Laparoscopic repair of inguinal hernias. World J Surg. 2011 Jul;35(7):1519-25. (License: CC BY-ND-4.0)