Abdominal Wall: Anatomy

Abdominal Wall: Anatomy

Spilios A. Pappas, MD

Table of Contents

Layers of the Abdominal Wall
Inguinal Anatomy
Femoral Anatomy

Laparoscopic Triangles

Layers of the Abdominal Wall

The Initial Response When Asked “What are the Layers of the Abdominal Wall” Should Be “Where?” – Muscle Layers Will Differ Based on Location

Layers of Abdominal Wall (Superficial-to-Deep)

  • Skin
  • Camper’s Fascia – Superficial Fatty Layer of the Superficial Abdominal Fascia
  • Scarpa’s Fascia – Deep Fibrous Layer of the Superficial Abdominal Fascia
  • Muscle Layers
  • Transversalis Fascia
  • Preperitoneal (Extraperitoneal) Fat
  • Parietal Peritoneum

Muscle Layers (Superficial-to-Deep)

  • Lateral to the Rectus Abdominis
    • External Oblique Muscle (EO)
    • Internal Oblique Muscle (IO)
    • Transversus Abdominis Muscle (TA)
  • Rectus Abdominis, Above Arcuate Line
    • Anterior Rectus Sheath – Aponeurosis of External Oblique and Half of the Internal Oblique
    • Rectus Abdominis
    • Posterior Rectus Sheath – Aponeurosis of Half of the Internal Oblique and the Transversus Abdominis
  • Rectus Abdominis, Below Arcuate Line
    • Anterior Rectus Sheath – Combined Aponeurosis of All the External Oblique, Internal Oblique, and Transversus Abdominis
    • Rectus Abdominis

Linear Structures

  • Arcuate Line: 2/3 Distance from Umbilicus to Pubic Crest
  • Linea Alba: Fibrous Midline of the Anterior Abdominal Wall Between the Two Rectus Abdominis Muscles
  • Semilunar Line (Spigelian Line): The Line Marking the Transition from Muscle to Aponeurosis of the Transversus Abdominis Muscle – Often Incorrectly Described as the Lateral Border of the Rectus Abdominis Muscle
  • EIT Ambivium: The Lateral Border of the Rectus Abdominis Muscle Formed by the External Oblique (E), Internal Oblique (I), and Transversus Abdominis (T) Muscles.

Sensory Nerves

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

Muscles of the Lateral Abdominal Wall: External Oblique (Left), Internal Oblique (IO), and Transversus Abdominis (Right)

Layers of the Abdominal Wall

Rectus Sheath: Above (Top) and Below (Bottom) the Arcuate Line

Inguinal Anatomy

Inguinal Canal

  • Passages within the Anterior Abdominal Wall Bilaterally
    • Males: Conveys the Spermatic Cord Contents
    • Females: Conveys the Round Ligament of the Uterus
  • Extends from the Deep Inguinal Ring to the Superficial Inguinal Ring
    • Deep Inguinal Ring: Opening within the Transversalis Fascia
    • Superficial Inguinal Ring: Opening within the Aponeurosis of the External Oblique
  • Borders/Walls:
    • Superior: Conjoint Tendon
    • Inferior/Floor: Inguinal Ligament
    • Posterior: Transversalis Fascia
    • Anterior: 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 Within:
    • Vas Deferens
    • Genital Branch of the Genitofemoral Nerve and the Sympathetic Testicular Nerves
    • Testicular Vessels
    • Pampiniform Plexus
    • Lymphatic Vessels

Ligaments

  • Conjoined Tendon: Combined Aponeurosis of the Internal Oblique and Transversus Abdominus Inserting into the Pubic Crest
  • Inguinal (Poupart’s) Ligament: A Fibrous Band Extending from the Anterior Superior Iliac Spine (ASIS) to the Pubic Tubercle
    • Formed by the Aponeurosis of the External Oblique
  • Lacunar Ligament: A Connection of the Inguinal Ligament to the Pectineal Ligament Where They Insert into the Pubic Tubercle
  • Pectineal (Cooper’s) Ligament: An Extension of the Lacunar Ligament Along the Pubic Bone

Inguinal (Hasselbach’s) Triangle: A Weakness within the Abdominal Wall Through Which Direct Inguinal Hernias May Protrude

  • Medial Border: Rectus Abdominis
  • Lateral Border: Inferior Epigastric Vessels
  • Inferior Border: Inguinal (Poupart’s) Ligament
  • Mnemonic: “RIP”

Nerves

  • Ilioinguinal Nerve: Cutaneous Sensation Over the Root of the Penis and Scrotum
    • Enters Through the Superior Border Between the Internal Oblique and Transversus Abdominis (Near the Iliohypogastric Nerve)
    • Runs Parallel Over the Spermatic Cord (Not Inside the Cord)
  • Iliohypogastric Nerve: Hypogastric Cutaneous Sensation
    • Enters Through the Superior Border Between the Internal Oblique and Transversus Abdominis (Near the Ilioinguinal Nerve)
    • Runs Transverse Over Internal Oblique, Superior to the Deep Ring
  • Lateral Femoral Cutaneous Nerve: Lateral Thigh Sensation
    • Initially Parallels the Ilioinguinal and Iliohypogastric Nerves
    • Exits Posterior to Inguinal Ligament Through Femoral Canal
  • Genitofemoral Nerve
    • Genital Branch: Cremaster Muscle Function and Scrotal Skin Sensation
      • Travels Through the Deep Ring to the Cremaster Muscle
    • Femoral Branch: Inner Thigh Sensation
      • Parallels the Iliac Vessels Through the Femoral Canal

Inguinal Canal

Ligaments: Inguinal (IL), Lacunar (LL), and Cooper’s (CL)

Inguinal (Hasselbach’s) Triangle

Nerves of the Inguinal Canal

Femoral Anatomy

Femoral Sheath: An Extension of Abdominal Fascia Extending from the Abdomen to the Thigh

  • Contains Three Compartments
  • Lateral Compartment: Femoral Artery
  • Intermediate Compartment: Femoral Vein
  • Medial Compartment: Contains Lymphatics (Known as the Femoral Canal)

The Femoral Nerve Passes Lateral to the Femoral Artery but Outside of the Femoral Sheath, Between the Iliacus and Psoas Major Muscles

Femoral Canal

  • The Medial and Smallest Compartment of the Femoral Sheath
  • Borders:
    • Anterior Border: Inguinal Ligament
    • Posterior Border: Cooper’s Ligament
    • Medial Border: Lacunar Ligament
    • Lateral Border: Femoral Vein
  • Contains Lymphatics, Connective Tissue, and Adipose Tissue
  • The Site of Potential Femoral Hernias

Structures Passing Under the Inguinal Ligament

  • Structures (Lateral to Medial):
    • Femoral Nerve
    • Femoral Artery
    • Femoral Vein
    • Femoral Canal (Lymphatics)
  • Mnemonic for Order:
    • “N.A.V.E.L. to the Navel”: Lateral to Medial (Nerve>Artery>Vein>Empty Space>Lymphatics)
    • “Venous to the Penis”: Vein is Medial to Artery

Femoral Sheath

Laparoscopic Triangles

Consider a “Mercedes Sign” Transected by the Inguinal Ligament

  • Superior Fork – Epigastric Vessels
  • Inferior/Lateral Fork – Testicular Vessels
  • Inferior/Medial Fork – Vas Deferens

Laparoscopic Inguinal Triangles

  • 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 and Testicular Vessels
    • Triangle of Pain: Lateral to the Testicular Vessels

Triangles of Danger

  • Triangles of “Danger” are Inferior to the Inguinal Ligament and Lateral to the Vas Deferens
  • “Triangle of Doom”
    • Borders: Vas Deferens, Testicular Vessels, and Peritoneal Fold
    • Contents: External Iliac Vessels
  • “Triangle of Pain”
    • Borders: Iliopubic Tract, Testicular Vessels, and Peritoneal Fold
    • Contents: Femoral Nerve, Femoral Branch of Genitofemoral Nerve, and Lateral Femoral Cutaneous Nerve
  • Avoid Laparoscopic Tacks and Sutures Inferior to Inguinal Ligament and Lateral to the Vas Deferens

Laparoscopic Inguinal Triangles

Laparoscopic View of the Inguinal Triangles 1

References

  1. Carter J, Duh QY. Laparoscopic repair of inguinal hernias. World J Surg. 2011 Jul;35(7):1519-25. (License: CC BY-ND-4.0)