Posterior Abdominal Wall Question and Answers

Diaphragm Muscles Of Posterior Abdominal Wall And Great Vessels Of Abdomen

Question 1. Describe the diaphragm (also called the Thoracoabdominal Diaphragm) under the following headings:

1. Thoracoabdominal Diaphragm Introduction
2. Thoracoabdominal Diaphragm Origin and insertion
3. Thoracoabdominal Diaphragm Openings of diaphragm and structure passing through them
4. Thoracoabdominal Diaphragm Nerve supply
5. Thoracoabdominal Diaphragm Actions
6. Thoracoabdominal Diaphragm Development and
7. Thoracoabdominal Diaphragm Applied Anatomy.

Answer:

1. Thoracoabdominal Introduction: The diaphragm is a large musculotendinous structure, which separates the thoracic cavity from the abdominal cavity.

2. Thoracoabdominal Origin: The diaphragm is divided into 3 parts (sternal, costal, and vertebral) and each part has its own origin.

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Diaphragm Origin:

• Sternal origin: By 2 fleshy slips from the back of the xiphoid process.
• Costal origin: By 6 fleshy slips from the inner surfaces of the lower 6 costal cartilages and adjacent parts of associated ribs.
• Vertebral origin:
  • From the upper 3 lumbar vertebrae by a pair of crura and associated median, medial, and lateral arcuate ligaments.
  • The crura (two) are tapering longitudinal tendinous structures attached to the upper 2 or 3 lumbar vertebrae.
  • The right crus is longer and stronger and attached to anterolateral surfaces of the upper 3 lumbar vertebrae and intervening intervertebral discs.
  • The left crus is shorter and attached on anterolateral surfaces of the upper two lumbar vertebrae and intervening intervertebral discs.
  • The medial arcuate ligament is a tendinous band that arches in front of the upper part of the psoas major from the body of the 2nd lumbar vertebra to the first lumbar transverse process.
  • The lateral arcuate ligament is a tendinous band that arches in front of the upper part of the quadratus lumborum from the first lumbar transverse process to the 12th rib.
  • The median arcuate ligament connecting the upper ends of two crura is tendinous and arches across the aorta.

Diaphragm Insertion: Into the central tendon, a trifoliate tendinous structure.

3. Thoracoabdominal Openings of Diaphragm: The diaphragm has openings to allow structures to pass from the thorax to the abdomen and vice versa.

There are three main openings in the diaphragm: Vena caval, Esophageal, and Aortic.

The vertebral level, shape, and location of these openings are given in the box below:

Structures passing through 3 major openings of the diaphragm are given in the box below:

4. Thoracoabdominal Nerve supply:

• Motor: By phrenic nerves (derived from ventral rami of C3, C4, and C5).
• Sensory:
  • Phrenic nerves provide sensory innervation to the central part.
  • Lower 6 thoracic nerves provide sensory innervation to the peripheral part.

5. Thoracoabdominal Actions: The diaphragm is a principal muscle of respiration. It also contracts during expulsive acts such as micturition and defecation.

6. Thoracoabdominal Development: The diaphragm develops from the following 4 sources

• Septum transverse
• Retroperitoneal membranes
• Lateral thoracic walls
• The dorsal mesentery of the esophagus

7. Thoracoabdominal Applied Anatomy:

• Posterolateral hernia of Bochdalek: It is a congenital hernia in which abdominal contents herniate into the thoracic cavity through a diaphragmatic gap in the costovertebral region.
• Sliding hernia: It is an acquired hernia in which the upper end of the stomach herniates into the thoracic cavity through the oesophageal hiatus due to weakness of the diaphragmatic muscle around this hiatus.

Muscles Of The Posterior Abdominal wall

Question 2. What are the muscles of the Posterior Abdominal Wall?
Answer:

Posterior abdominal wall: They are 3 in number

1. Psoas major
2. Iliacus
3. Quadratus lumborum

Question 3. Give the origin, insertion, nerve supply, and actions of the psoas major muscle.
Answer:

Psoas major muscle is a large fusiform muscle placed along the side of the lumbar vertebral column and pelvic brim.

Psoas major muscle Origin:

• By 5 slips from the anterior surfaces and lower borders of transverse processes of all the lumbar vertebrae.
• By 5 slips, from each intervertebral disc and the adjacent margins of two vertebrae between T12 to L5 vertebrae.
• From 4 fibrous arches that bridge across the sides of the upper 4 lumbar vertebral bodies.

Psoas major muscle Insertion: By a rounded tendon into the tip and anterior surface of the lesser trochanter of the femur.

Psoas major muscle Nerve supply: By the branches from roots of lumbar plexus (ventral rami of L2, L3, and sometimes L4).

Psoas major muscle actions:

• Medial rotation, flexion, and lateral rotation of the thigh in sequence
• It flexes the trunk on the lower limb as in a stooping position.
• It flexes the vertebral column forward and sideward.
• It along with iliac us is a powerful flexor of the hip joint as in raising the trunk from recumbent to sitting position.

Question 4. Write a short note on the psoas sheath and discuss its clinical significance.
Answer:

The psoas major muscle is enclosed in the fascial sheath called the psoas sheath. It is formed by the psoas fascia.

• The pus from the tubercular lumbar spine cannot spread anteriorly due to attachment of anterior longitudinal ligament on the vertebral column, and therefore, it passes laterally into the psoas sheath.
• Pus from the +tubercular thoracic spine may also enter the psoas sheath by tracking down from the posterior mediastinum, as the sheath is open above and communicates with the posterior mediastinum.
• Sometimes pus spreads under the inguinal ligament into the femoral triangle where it produces a soft swelling.

Occasionally, in neglected cases, pus tracks along the femoral vessels into the sub-sartorial canal and eventually may produce swelling in the popliteal fossa.

Question 5. Enumerate the nerves that appear in relation to the psoas major muscle.
Answer:

Seven nerves appear in relation to the psoas major muscles.

• One Anteriorly: Genitofemoral nerve (L1, L2).
• Two Medially: Obturator nerve and the lumbosacral trunk.
• Four Laterally: From above downward; iliohypogastric nerve, ilioinguinal nerve, lateral cutaneous nerve of the thigh, and femoral nerve.

Great Blood Vessels Of The Abdomen

Question 6. Describe the abdominal aorta under the following headings:

1. Introduction
2. Branches
3. Development and
4. Applied anatomy.

Answer:

1. Abdominal aorta Introduction:

• It is the continuation of descending thoracic aorta at the aortic orifice of the diaphragm at the level of the lower border of T12 vertebra and terminates at the lower border of the L4 vertebra by dividing into two common iliac arteries.
• It lies in front of the upper 4 lumbar vertebrae behind the peritoneum.

2. Abdominal aorta Branches: These are in 4 sets:

1. Three unpaired anterior branches, to the viscera:
   1. Coeliac artery, also called coeliac axis/coeliac trunk, at the level of T12.
   2. Superior mesenteric artery, at the level of L1.
   3. Inferior mesenteric artery, at the level of L3.
2. Three paired lateral branches, to the viscera:
   • Middle suprarenal arteries, at the level of L2.
   • Renal arteries, at the level of L1.
   • Gonadal arteries (testicular or ovarian), at the level of L2.
3. Five paired lateral branches, to the parities:
   • Inferior phrenic arteries, at the level of T12.
   • Four lumbar arteries (arising from the posterior aspect of the aorta).
   • Two terminal branches:
   • Right and left common iliac arteries, at the level of L4.
4. One unpaired posterior branch: Median sacral artery arises slightly above the bifurcation of the aorta, at the level of L4.

3. Abdominal aorta Development: The abdominal aorta develops in the 3rd week of IUL by the fusion of two primitive dorsal aortae.

4. Abdominal aorta Applied anatomy:

• Aortic pulsations: They can be felt just below and slightly to the left of the umbilicus in thin individuals with abdominal muscles relaxed.
• Aortic aneurysm (localized dilatation of aorta): It commonly (95%) occurs below the origin of renal arteries.
• Coarctation of abdominal aorta (stenosis): If this occurs, it is fatal because of less blood supply to the kidneys.

Question 7. Describe Inferior Vena Cava under the following headings:

1. Inferior Vena Cava Introduction
2. Inferior Vena Cava Tributaries and
3. Inferior Vena Cava Development.

Answer:

1. Inferior vena cava Introduction:

• It is largest vein of the body, which drains venous blood from body below the diaphragm.
• It extends (below upward) from L5 to T8 vertebra.
• It forms on the right side of the front of L5 vertebra and terminates by opening into the right atrium.
• It is 9″ long and 1″ in breadth.

2. Inferior vena cava Tributaries There are 12 tributaries:

• 2 common iliac veins
• 2 renal veins
• 2 hepatic veins
• 2 phrenic veins
• 2 lumbar veins (3rd and 4th)
• Right suprarenal vein
• Right testicular (or ovarian) vein

Note: Tributaries of inferior vena cava do not correspond to branches of the abdominal aorta.

3. Inferior vena cava Development:

• It is the composite vessel and develops in the 8th week of IUL from the following sources.
• From below upward, these are:
• The persistent caudal part of the right posterior cardinal vein (1).
• Right supra cardinal vein (2).
• Anastomosis between right supra cardinal and right sub cardinal veins (3).
• The upper part of the right sub-cardinal vein (4).
• The anastomotic channel between the right subcarinal and right hepatocardiac channel (5).
• Right hepatocardiac channel (6).

Note: Common developmental anomalies of the inferior vena cava are: Double inferior vena cava and Preureteric inferior vena cava/retrieval ureter.

Inferior vena cava Summary:

Inferior vena cava is derived from the following sources:

• The caudal part of the right posterior cardinal vein
• Right supra cardinal vein
• Anastomosis between right supra and sub cardinal veins
• The upper part of the right sub-cardinal vein
• Anastomosis between the right subcardinal vein and hepatocardiac channel