Abdominal Wall Anatomy: Inguinal Canal and Hernia

Inguinal Canal

• The inguinal canal has an oval shape with 2 structures in each wall:
  • Anterior wall: external oblique and part of internal oblique
  • Roof: lower arching fibers of internal oblique and transversus abdominis
  • Posterior wall: fascia transversalis and conjoint tendon (medial half)
  • Floor: inguinal ligament
• The lateral 1/2 of the posterior wall is weak because it is formed of fascia transversalis only

Contents of Inguinal Canal

• Male: ilio-inguinal ligament, spermatic cord (vessels, nerves, lymphatics, and duct)
• Female: round ligament of uterus, ilio-inguinal nerve

Spermatic Cord

• Coverings: internal spermatic fascia, cremasteric fascia and muscle, external spermatic fascia
• Contents: testicular artery, artery of the vas deferens, cremasteric artery, cremasteric nerve, ilioinguinal nerve, sympathetic plexus, vas deferens, pampiniform plexus of veins, lymphatics, and vestige of the processus vaginalis

Abdominal Wall Layers

• Below the umbilicus, superficial fascia is formed of 2 layers: Camper's fascia (superficial fatty layer) and Scarpa's fascia (deep membranous layer)

Anterior Abdominal Wall Muscles

• 6 muscles: external oblique, internal oblique, transversus abdominis, rectus abdominis, pyramidalis, and cremasteric muscle
• External oblique: origin at the outer surface of the lower 8 ribs, insertion at the xiphoid process, linea alba, pubic crest, tubercle, and ASIS
• Linea alba: formed by the aponeuroses of right and left external obliques, extending from the xiphoid process to the symphysis pubis

Inguinal Ligament (Poupart's Ligament)

• Definition: thickened lower free border of the external oblique aponeurosis
• Extension: between the pubic tubercle and the anterior superior iliac spine
• Laterally: gives attachment to 2 muscles

Deep Inguinal Ring

• Deficiency in fascia transversalis
• Located ½ an inch above the midpoint of the inguinal ligament

Layers of the Scrotum

• 1. Skin
• 2. Dartos muscle
• 3. Membranous layer of the superficial fascia (Colle's fascia)
• 4. External spermatic fascia
• 5. Cremasteric muscle and fascia
• 6. Internal spermatic fascia
• 7. Parietal layer of tunica vaginalis

Mechanisms of the Inguinal Canal

• Flap valve mechanism: compression of ant. and post. walls during the rise of intra-abdominal pressure
• Shutter mechanism: contraction of internal oblique muscle approximating the roof and floor of the canal
• Ball valve mechanism: contraction of the cremasteric muscle elevating the testis and plugging the superficial ring

Hernia

• Definition: protrusion of any abdominal viscus through a weak point of the abdominal wall
• Types: external hernia (appears on the surface) and internal hernia (does not appear on the surface)
• Etiology: weakness of the abdominal wall and increased intra-abdominal pressure
• Structure: sac, content, and coverings

Inguinal Hernia

• Types: indirect (oblique) and direct
• Indirect inguinal hernia: processus vaginalis has remained open, common in young males, and usually extends into the scrotum

Femoral Hernia

• Clinical importance: femoral canal dead space for distension of the femoral vein during muscular exercise
• Pathway for lymph vessels from the lower limb to the abdomen and pathway for femoral hernia
• Common in females due to a wide femoral ring and small-sized femoral vein

Transversus Abdominis Plane (TAP) Block

• Definition: a peripheral nerve block designed to anesthetize the nerves supplying the anterior abdominal wall (T6 to L1)