Anatomy of Posterior abdominal wall
- Superiorly 12th rib
- Medially, lumbar vertebrae L1-L5
- The disc of the L5 / S1 vertebrae is on the sacrum.
- Ala (2)
- Ala of the sacrum
- Ala of the ilium
- These are joined by the sacral iliac joint.
- Iliac fossa = the anterior surface of the ala of the ilium.
Muscular component of Posterior abdominal wall
|Psoas Major||Ventral branches of L2-L4||Transverse Processes of LumbarBodies and Discs of T12-L5||Lesser Trocanter of Femur||Flex ThighFlex Verterbral Column|
|Psoas Minor||Ventral branches of spinal nerves L1-L2||Bodies of the T12 & L1 vertebrae||Iliopubic eminence at the line of junction of the ilium and the superior pubic ramus||Flexes & laterally bends the lumbar vertebral column|
|Iliacus||Femoral N. (L2-L4)||Superior 2/3 of Iliac FossaAla of SacrumAnterior Sacroiliac Lig.||Lesser Trocanter of FemurPsoas Major Tendon||Flex ThighActs with Psoas Major|
|Quadratus Lumborum||Ventral Branches of T12 and L1-L4 nerves||Medial half of 12th RibTransverse Processes of Lumbar||Iliolumbar LigamentInternal Lip of Iliac Crest||Extends and Flexes Vertebral Column|
- Iliacus combined with psoas major forms the iliopsosas muscle which is the chief flexor of the thigh.
- The Iliopsoas test:
- abdominal viscera will rest on these muscles (such as cecum, appendix on right side pancreas is superior / on left side, sigmoid colon).
- Inflammation of these associated organs can be checked for by flexing the iliacus / psosas.
- A positive psoas sign is pain when flexing the iliopsoas, thus showing irritation of the muscle by some entity in the abdominal cavity.
- Acute appendicitis will have right side positive psoas test.
The fascia of the posterior abdominal wall (cross-section at L2)
- At midline, have crus of diaphragm right against the vertebrae. These Right and Left crus give rise to the median arcuate ligament (behind which the Aorta passes)
- Just lateral, find the psoas muscle
- fascia of psoas superiorly forms the medial arcuate ligament associated with diaphragm
- inferiorly, the fascia extends into the thigh.
- A psoas abscess is an infection that has traveled from the lumbar vertebrae to the psoas (such as tuberculosis).
- This abscess may end up draining through skin in upper thigh region.
- Laterally / posteriorly to psoas, have Quadratus lumborum. The fascia superiorly forms the lateral arcuate ligament of the diaphragm.
- Thoracolumbar fascia:
- The posterior layer is the strongest and passes from the lumbar spines, superficial to the erector spinae, to fuse with the middle layer lateral to that muscle.
- The middle layer separates the erector spinae from the quadratus lumborum. The erector spinae contributes to this layer.
- Anterior “quadratus” layer:
- is thin but strong and covers the anterior aspect of the quadratus lumborum (which has fascia contributing to this layer)
- Superiorly it is thickened to form the lateral lumbocostal arch which gives attachment to the diaphragm.
- Latissimus dorsi has attachment on thoracolumbar fascia.
- The thoracolumbar fascia is anchored on erector spinae, transverse processes, quadratus lumborum.
- Location: on the posterior abdominal wall behind the parietal peritoneum.
- Extent: twelfth thoracic vertebra and the twelfth rib to the sacrum and the iliac crests below.
- Variable amount of fatty connective tissue
- Suprarenal glands & the kidneys
- ureters and the renal and gonadal blood vessels.
- Pancreas, Duodenum +/-ascending and descending parts of the colon
Mnemonic of Retroperitoneal Organs
Abdominal aorta Paired tributaries
- Supply posterior abdominal wall and organs associated there.
- Aorta eventually bifurcates at L4 body. The highest point of iliac crest is just above this bifurcation. Also corresponds with umbilicus (slightly to the left of the umbilicus).
- Branches into R and L common iliac → branch into internal / external iliac. The external iliac becomes the femoral.
- Along common iliac: have branch = iliolumbar artery. Comes off and branches
- Branch to Iliacus muscle
- Another branch travels superiorly and supplies psoas and quadratus lumborum (sometimes called ascending lumbar artery).
- Renal arteries at L1 level.
- Inferior phrenic arteries:
- supply diaphragm
- have branch = superior superrenals
- Lumbar arteries – supply vertebrae and muscles of posterior abdominal wall.
- Gonadal branches: are either testicular or ovarian, Travel down to supply those structures.
- Aortic aneurysm: associated with abdominal aorta.
- Refers to a weakness in the wall of an artery that is worked on by pressure. The wall will balloon out.
- May grow to the size of a softball. It pulses along with aorta, may palpate it.
- When people fall from great heights, have a ruptured abdominal aorta. Aortic aneurysms are 90% lethal.
- Aortic aneurysm: associated with abdominal aorta.
Inferior vena cava
- Just to the right of the abdominal aorta. Has no valves, is the largest vein in the body.
- Comes through vena cava hiatus in the diaphragm.
- Bifurcates at L5 into 2 common iliac veins.
- Lacks unpaired tributaries instead:
- Has hepatic veins which enter the IVC & are short and are within the liver.
- Right gonadal vein.
- Has inferior phrenic veins, suprarenal veins lumbar veins (at L1 and L3) as tributaries
- Because it is Right displaced, the left renal vein is longer.
- This longer left vein will receive inputs from vessels that would contribute to the IVC on the right side (such as left gonadal, left suprarenal etc.).
- Visceral nodes – found on organs and mesentery.
- Pass from organs to mesentery to celiac nodes on either side of celiac trunk or to superior mesenteric nodes (terminal nodes)
- Inferior mesenteric nodes
- Parietal nodes:
- Associated with abdominal wall and large arteries
- Drain into external iliac b into common iliac → into cysternae chyli.
- Lymph flows from visceral → parietal lymph nodesà cysterna → chyle (larger dilated lymphatic vessel behind the IVC). It is continuous with thoracic duct.
Innervation of posterior abdominal wall (somatics)
- Subcostal nerve – T12
- travels under rib 12. travels between internal oblique and transverse abdominus.
- Gives off cutaneous branches.
- Lumbar plexus – L1-L5 ventral rami. Located in the psoas.
- Iliohypogastric – L1- supplies muscles of lower abdominal wall as well as skin of lower abdominal wall, hip, upper thigh.
- Ilioinguinal – L1 – travels into scrotum / labia majora
- Genitofemoral – L1-2 – on anterior surface of psoas major. Travels toward anterior part of pelvis and branches
- Anterior surface of thigh
- Medial branch into inguinal canal = genital branch to cremaster muscles.
- Lateral femoral cutaneous – L2-3. travels more laterally on surface of iliacus muscle. Passes under the inguinal ligament close to origin on ASIS. Supplies lateral aspect of thigh.
- Femoral – L2-4- largest nerve in plexus. Tucked under psoas major. Supplies extensors of knee.
- Obturator – L2-4. on medial aspect of psoas major. Drops into true pelvis and through a foramen = operator canal. Supplies muscles on medial aspect of thigh = major adductors of thigh.
- Lumbosacral trunk – L4-5- most medial of plexus. Contributes to sacral plexus. Runs over ala of the sacrum.
- The Posterior Abdominal Wal @ TeachMeAnatomy
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- Posterior Abdominal Wall @ Lecturio