T1 L3: Anterior abdominal wall and inguinal canal

• Boundaries of the abdominal cavity

  abdominal viscera supported superiorly by the thoracic cage and inferiorly by the pelvic girdle.

  Superior boundary: diaphragm

  Inferior boundary: pelvic inlet

  
• Pelvic inlet 


  Above pelvic inlet: false pelvis / abdominal cavity

  Below pelvic inlet: true pelvis / part of pelvic cavity

  
• Innominate bone


  Main parts:

  Yellow: ilium

  Blue: Ischium

  Red: Pubis

  1. pubic tubercle
  2. Pubic crest
  3. Anterior inferior iliac spine (AIIS)
  4. Anterior superior iliac spine (ASIS)
  5. iliac tubercle
  6. iliac crest
  7. iliac fossa
  8. posterior superior iliac spine (PSIS)
  9. posterior inferior iliac spine (PIIS)

  
• Pelvic girdle


  formed by two innominate bones

  1. sacrum
  2. ASIS
  3. Inguinal ligament
  4. pubic tubercle
  5. coccyx

  
• What is the inguinal ligament?

  The boundary between abdominal wall and thigh
• Planes dividing the 9 regions of the abdomen

  1. Vertical planes: midclavicular lines
  2. Superior horizontal plane: inferior border of 10th costal cartilage (subcostal)
  3. Inferior horizontal plane: between tubercles of iliac crests (transtubercular)

  
• 9 regions of the abdomen

  1. hypochondriac
  2. flank (lumbar)
  3. groin (inguinal)
  4. umbilical
  5. hypogastric (pelvic)
  6. epigastric

  
• Quadrants of the abdomen

  Plane 1: Median plane (vertical)

  Plane 2: Trans-umbilical plane (horizontal)

  Quadrants:

  Right upper

  Left upper

  Right lower

  Left lower

  
• Layers of the abdominal wall

  from superficial to deep:

  1. skin
  2. superficial fatty layer (Camper's Fascia)
  3. deep membranous layer (Scarpa's Fascia)
  4. External oblique muscle
  5. Internal oblique muscle
  6. Transversus abdominis muscle
  7. Transversalis fascia
  8. Extraperitoneal fat
  9. Parietal peritoneum
  10. Investing fascia:
  11. superficial
  12. intermediate
  13. deep

  
• Linea Alba 


  formed by the union of aponeuroses (tendon for flat muscle) of the anterolateral abdominal wall muscles

  
• Lateral abdominal wall muscles - External oblique


  origin: ribs 5-12

  insertion: linea alba, pubic tubercle, iliac crest

  runs forwards and down (hands in front pockets)

  thickened inferior border forms inguinal ligament

  actions: compress abdominal contents, flex trunk (bilateral), lateral flexion of trunk (unilateral), trunk rotation (unilateral)

  
• Later abdominal wall muscles - Internal oblique 


  origin: thoracolumbar fascia, iliac crest, inguinal ligament

  insertion: ribs 10-12, linea alba, pubic crest (via conjoint tendon)

  direction: downwards and outwards (hands in back pockets)

  actions: compress abdominal contents, flex trunk, lateral flexion of trunk, trunk rotation

  
• Lateral abdominal wall muscles - Transversus abdominis


  origin: ribs 7-10, costal cartilage, thoracolumbar fascia, iliac crest, inguinal ligament

  insertion: linea alba, pubic crest (via conjoint tendon)

  direction: runs horizontally

  action: compress abdominal contents

  
• Thoracolumbar fascia 


  thoracic and lumbar parts of the deep fascia enclosing the intrinsic back muscles
• Anterior abdominal wall muscles - Rectus abdominis 


  origin: pubic crest, pubic tubercle, pubic symphysis

  insertion: costal cartilages of ribs 5-12, xiphoid process

  action: compress abdominal contents, flex trunk

  
• Anterior abdominal wall muscles - Pyramidalis 


  origin: pubic symphysis

  insertion: linea alba

  action: none

  
• Surface anatomy - Rectus abdominis

  verticle line separating 'abs' with lateral muscle is called Linea semilunaris

  
• Superior rectus sheath


  internal oblique aponeurosis splits into two layers:

  • Anterior laminae: passes anterior to rectus abdominis
  • Posterior laminae: passes posterior to rectus abdominis

  
• Inferior rectus sheath 


  underneath the Arcuate line: 1/3rd distance between umbilicus and pubic crest

  all aponeuroses pass anterior to rectus abdominis

  
• Compression of abdominal contents

  Breathing: abdominal muscles relax during inspiration and contract during forced expiration

  Breath held (diaphragm fixed): contraction of the abdominal wall muscles increases pressure inside the abdominopelvic cavity and assits with urination, defecation and childbirth.

  
• Innervation of abdominal wall

  Nerves run in neurovascular plane between internal oblique and transversus abdominus muscle.

  • T7 - T11: thoracoabdominal nerves
  • T12: subcostal nerve
  • L1 splits into:
  • iliohypogastric nerve
  • ilioinguinal nerve

  
• Arterial supply to the anterior abdominal wall

  Label

  1. Subclavian artery
  2. Internal thoracic artery
  3. intercostal artery (travels anteriorly in ribcage)
  4. Musculophrenic artery (travels underneath ribcage)
  5. Superior epigastric artery
  6. inferior epigastric artery
  7. Deep circumflex iliac artery
  8. Superficial circumflex iliac artery
  9. femoral artery

  
• Epigastric arteries and rectus sheath haematoma

  Superior and inferior epigastric arteries run within the rectus sheath and anastamose over the anterior abdominal wall.

  Rectus Sheath Haematoma:

  rupture in one of the epigastric arteries with blood accumulation within rectus sheath

  can spread into abdominal cavity

  Risk factors: use of anticoagulants

  
• Inguinal canal 


  an oblique passage (tunnel) that extends downwards and medially though the lower anterior abdominal wall

  1. Deep inguinal ring: entrance to canal between anterior superior iliac spine (ASIS) and pubic tubercle. Opening through transversalis facia.
  2. Superficial inguinal ring: exit of canal close to pubic tubercle. Opening through external oblique aponeurosis

  
• Borders of the inguinal canal

  1. anterior border: external oblique aponeurosis, laterally also internal oblique
  2. superior border: internal oblique and transversus abdominis
  3. Posterior border: transversalis fascia, medially conjoint tendon
  4. inferior border: inguinal ligament (formed by the thickened inferior border of external oblique)

  
• Layers of spermatic cord, scortum and testis (Some Dangerous Englishman Called It The Testes)

  Skin

  Dartos fascia + muscle

  External spermatic fascia

  Cremaster muscle

  Cremasteric fascia

  Internal spermatic fascia

  Tunica vaginalis
• Gonads

  • Originally develop in the abdomen (close to posterior abdominal wall)
  • Gubernaculum attached to inferior pole of gonad
• Descent of the gonads

  1. By 12th week the testis is in the pelvis

  2. By 28 weeks it lies close to the developing deep inguinal canal ring

  3. Processus vaginalis (an extension of peritoneum), herniates through abdominal accompanied by layers of abdominal wall

  4. Between weeks 28-32 the testis pass through the inguinal canal into the scrotum, guided by the gubernaculum

  5. Process vaginalis closes, the remaining part in the scrotum becomes the tunica vaginalis (parietal and visceral layers)
• Layers of the scrotum

  Label

  1. skin
  2. Dartos fascia and muscle
  3. external spermatic fascia
  4. cremaster muscle and fascia
  5. internal spermatic fascia
  6. parietal layer of tunica vaginalis
  7. testis covered by visceral layer of tunica vaginalis

  
• Contents of the inguinal canal

  Males: spermatic cord and ilioinguinal nerve

  • Spermatic cord:
  • ductus vas deferens
  • Arteries: testicular artery, artery of ductus deferens, cremasteric artery
  • Veins: pampiniform plexus (from testicular veins)
  • Nerves: genital branch of genitofemoral nerve, sympathetic nerve fibres
  • Females:
  • round ligament
  • ilioinguinal nerve L1
  • genital branch of genitofemoral nerve

  
• Inguinal hernias 


  Protrusion of gut or omentum (peritoneum containing fat) through the inguinal canal. more common in males.

  2 types:

  1. Direct (acquired): hernia passes directly through abdominal wall and exits through the superficial inguinal ring. Medial to inferior epigastric artery.
  2. Indirect (congenital): hernia passes through the length of the canal through the superficial and deep inguinal rings. Lateral to inferior epigastric artery.