Posterior Abdominal Wall Anatomy Notes

Posterior Abdominal Wall

Structures Along the Posterior Abdominal Wall

• Kidneys
• Suprarenal glands
• Urinary Bladder
• Ureters
• Rectum
• Inferior Vena Cava
• Abdominal Aorta
• Renal Vessels
• Common Iliacs
• Gonadal vessels

Bones of the Posterior Abdominal Wall

• Bony Elements
  • Lumbar Vertebrae
  • Wing of the ilium
  • Sacrum

Muscles of the Posterior Abdominal Wall

• 4 Muscles
  • Quadratus Lumborum
  • Psoas Major
  • Psoas Minor
  • Iliacus

Posterior Abdominal Wall

• Skeleton
  • 5 Lumbar Vertebrae & IVDs
  • Upper sacrum
  • Iliac crests
• Muscles
  • Thoracolumbar fascia
• Arteries
  • Abdominal aorta & branches
• Veins
  • Inferior vena cava & branches
• Nerves
• Lymphatics

Arteries

• Abdominal Aorta & Branches
  • Descends anterior to bodies of T12 – L4 vertebrae
• Vessel Vertebral Level
  • Celiac Trunk T12
  • Superior Mesenteric Artery L1
  • Renal Arteries L1
  • Gonadal Arteries L2
  • Inferior Mesenteric Artery L3
  • Aortic Bifurcation L4
  • Lumbar Arteries L1-L4
  • Median Sacral Artery L4

Veins

• Posterior abdominal wall veins drain directly into IVC
• EXCEPT left gonadal vein & left suprarenal vein
• IVC begins at L5 to the right of the midline

Lymph System

• Drains surplus tissue fluid to blood stream
• Pathway for removal of cellular debris from decomposition & infection
• Absorption & transport of dietary fat
• Body defense
• Activation & production of B & T lymphocytes
• Antibody formation
• System of vessels, nodes & lymphoid organs
• Lymphoid organs
  • Thymus
  • Red bone marrow
  • Spleen
  • Tonsils
  • Alimentary tract & appendix lymphoid nodules

Lymphatic Drainage

• Lymphoid organs & tissues in alimentary system:
  • Mucosa-associated lymphoid tissue (MALT)
  • Gut-associated lymphoid tissue (GALT)
  • Tonsils
  • Peyer’s Patches
  • Appendix
  • Respiratory (BALT)
  • Nasal (NALT)
  • Eye (CALT)
  • Vaginial (VALT)
  • Lacteals
    • Specialized lymphatic vessels that absorb fat in villi of the jejunum & ileum that absorb fat

Superficial Lymphatic Drainage

• Anterolateral Abdominal Wall:
  • Superior to transumbilical plane
    • Drain into axillary lymph nodes and parasternal lymph nodes
  • Inferior to transumbilical plane
    • Drain into superficial inguinal lymph nodes
  • Superficial vessels drain to deep lymphatic vessels and nodes
    • External iliac, common iliac, right and left lumbar lymph nodes

Lymphatic Drainage

• Right lymphatic duct
  • Drains right upper quadrant
  • Right side of head, neck, thorax and upper extremity
  • Enters venous system at right venous angle
• Thoracic duct
  • Drains remainder of body
  • Ascends from cisterna chyli
  • Enters venous system at left venous angle
• Cisterna chyli – next slide!

Lymphatic Drainage

• Cisterna chyli:
  • Union of lumbar & intestinal trunks
  • Receives all lymph from lower half of body
  • Drains to thoracic duct
  • 20-50% of lymph entering thoracic duct comes from the liver
  • Anterior to L1-L2 vertebral bodies
  • Between IVC & abdominal aorta

Abdominal Lymphatics

• All abdominal and pelvic lymph drains back to cisterna chyli
• Drainage to cisterna chyli follows blood vessels
• Major trunks and nodes located along aorta
  • Celiac lymph nodes
  • Superior mesenteric lymph nodes
  • Inferior mesenteric lymph nodes
  • Pre-aortic lymph nodes

Muscles - Diaphragm

• Primary muscle of respiration
  • Descends during inspiration
• Origins:
  • Sternal – xiphoid process
  • Costal – internal surfaces of inferior six costal cartilages
  • Lumbar – medial & lateral arcuate ligaments and three superior lumbar vertebrae
• Insertion:
  • Central tendon

Muscles - Diaphragm

• Medial arcuate ligament
  • Body of L1 to TP of L1
  • Arches over psoas major
• Lateral arcuate ligament
  • TP of L1 to 12th rib
  • Arches over quadratus lumborum

Muscles - Diaphragm

• Right crus
  • Arises from first three or four lumbar vertebrae & intervertebral disks
  • Larger and longer than left crus
• Left crus
  • Arises from first two or three lumbar vertebrae & intervertebral disks

Muscles - Diaphragm

• Openings:
  • Caval opening (T8)
    • IVC
    • Opening in central tendon
  • Esophageal hiatus (T10)
    • Esophagus
    • Right & left vagal trunks
    • Forms the right crus
  • Aortic hiatus (T12)
    • Aorta, thoracic duct, azygos and hemiazygous veins
    • Opening posterior to diaphragm
    • Median arcuate ligament
    • Right & left cura unite in midline to form

Muscles - Diaphragm

• Arterial Blood Supply
  • Thoracic Aorta
    • Superior phrenic arteries
  • Internal Thoracic Arteries
    • Musculophrenic arteries
    • Pericardiophrenic arteries
  • Abdominal Aorta
    • Inferior phrenic arteries
• Venous Drainage
  • Veins mirror arteries & drain to IVC

Muscles - Diaphragm

• Innervation
  • Phrenic nerve (C3-C5)
    • Motor & sensory
  • Lower 6-7 intercostal nerves
    • T5-T11
    • Sensory
  • Subcostal nerve
    • T12
    • Sensory

Muscles - Psoas Major

• Superior Attachment
  • Transverse processes of lumbar vertebrae
  • Sides of T12-L5 vertebral bodies & IVDs
• Inferior Attachment
  • Lesser trochanter, Femur
• Innervation
  • Anterior rami of lumbar nerves L1-3
• Primary Actions
  • Flexes the thigh (acting with iliacus)
  • Flexes trunk when sitting (acting with iliacus)
  • Flexes the vertebral column laterally
  • Balances trunk
  • Psoas minor sometimes present

Muscles - Iliacus

• Superior Attachment
  • Superior two-thirds of iliac fossa
  • Ala of sacrum
  • Anterior sacroiliac ligaments
• Inferior Attachment
  • Lesser trochanter, femur & diaphysis inferior to trochanter
  • Psoas major tendon
• Innervation
  • Femoral nerve (L2-4)
• Primary Action
  • Acting with psoas major flexes thigh & stabilizes hip joint

Muscles - Iliopsoas

• Refers to the integration of the inferior fibers of psoas major/minor with iliacus fibers
• Major flexor of the thigh & hip stabilizer

Muscles - Quadratus lumborum

• Superior Attachment
  • Medial one-half of 12th rib inferior border
  • Tips of lumbar TPs
• Inferior Attachment
  • Iliolumbar ligament
  • Internal lip of iliac crest
• Innervation
  • Anterior rami T12 (subcostal nerve)
  • Lumbar plexus (L1-4)
• Primary Action
  • Extends & laterally flexes vertebral column
  • Fixes rib 12 during inspiration

Muscles - Transversus Abdominis

• Transversus abdominis
• Oblique muscles posterolateral wall

Muscles Summary Table

Nerves of The Posterior Abdominal Wall

• 7 Nerves
  • Subcostal
  • Iliohypogastric
  • Ilioinguinal
  • Genitofemoral
  • Obturator
  • Lateral femoral cutaneous
  • Femoral

Path of the Nerves in the Posterior Abdominal Wall

The Lumbar Plexus

• Subcostal n. (T12) - passes along the inferior border of the 12th rib and under the lateral arcuate ligament, it supplies pyramidalis m. and skin over the anterior gluteal region and greater trochanter.
• L1 ventral ramus
  • Iliohypogastric - runs across transversus abdominalis and internal oblique, supplies them, then passes into the skin and supplies the skin in the suprapubic region.
  • Ilioinguinal - Innervates internal oblique, passes through inguinal canal and innervates skin along the proximomedial thigh, root of penis, upper scrotum or mons pubis and labia majora
• Genitofemoral (L1-L2) - runs through and across psoas major and divides into femoral and genital branches.
  • genital branch - enters inguinal canal and supplies cremaster and scrotal skin.
  • femoral branch - passes under the inguinal ligament and innervates skin over the femoral triangle.
• Lateral femoral cutaneous (L2-L3) - runs over iliacus to pass under the inguinal ligament and supply the skin over the lateral thigh

The Lumbar Plexus cont…

• Obturator (L2-L4) - emerges from medial border of psoas major and enters the thigh via the obturator foramen. Innervates adductors of the thigh and innervates a patch of skin medial and above the knee.
• Femoral (L2-L4) - emerges from the lateral border of psoas major and separates into several anterior femoral cutaneous branches and the saphenous n. either before or after it passes under the inguinal ligament. It supplies knee extensors and thigh flexors. It provides sensation to most of the anteriomedial thigh.
• LUMBOSACRAL TRUNK leading to the lumbosacral plexus

Autonomic Nerves

Sympathetic

• Sensory afferent (pain)
• GI tract to left colic flexure travels
  • Greater Splanchnic Nerve (T5-9, sometimes T10)
  • Lesser Splanchnic Nerve (T10-T11)
  • Least Splanchnic Nerve (T12)
• Left colic flexure to rectum
  • Lumbar Plexus (L1-3)

Parasympathetic

• Sensory afferent (reflexes)
• GI tract to left colic flexure
  • Vagus Nerve (CN X) from vagal plexuses
• Left colic flexure to rectum
  • Pelvic Splanchnic Nerves (S2-4)

Lumbar & Sacral Splanchnic Nerves

• Lumbar Splanchnic Nerves
  • 4 Nerves
  • Superior & Inferior Hypogastric plexuses
    • Neck of urinary bladder, ductus deferens, prostate
• Sacral Splanchnic Nerves
  • Other pelvic viscera

Autonomic Nerves

Sympathetic

• Sensory afferent (pain)
• GI tract to left colic flexure travels
  • Greater Splanchnic Nerve (T5-9, sometimes T10)
  • Lesser Splanchnic Nerve (T10-T11)
  • Least Splanchnic Nerve (T12)
• Left colic flexure to rectum
  • Lumbar Plexus (L1-3)

Parasympathetic

• Sensory afferent (reflexes)
• GI tract to left colic flexure
  • Vagus Nerve (CN X) from vagal plexuses
• Left colic flexure to rectum
  • Pelvic Splanchnic Nerves (S2-4)

Autonomic Nerves Spinal Levels for Abdominal organs: