L2. Anatomy Of The Posterior Abdominal Wall

Question 1

Describe the Paravertebral gutters

Answer 1

The 5 lumbar vertebrae project into the abdominal cavity quite significantly (sit forwards) and the ribs arch backwards from the vertebral column and then around.

This creates a pair of PARAVERTEBRAL GUTTERS which sit on either side (and behind) of the column.These gutters are floored by powerful longitudinal muscles: these form the posterior abdominal wall.

Question 2

What are the four major muscles of the posterior abdominal wall?

Answer 2

Psoas Major
Psoas Minor
Quadratus Lumborum
Iliacus Muscle

Question 3

Where does the pair of psoas major muscles lie? And what is the general shape of the muscle?

Answer 3

It lies in the paravertebral gutter between the bodies and the transverse processes (it overlies the transverse processes) of the lumbar vertebrae.

The lateral border is straight and cuts obliquely through the body.

Question 4

What are the origins of the psoas major muscle?

Where does the psoas major muscle insert?

Answer 4

It has one continuous origin from the lumbar vertebral column AND the discs AND the medial ends of the transverse processes = high strength

Fibres converge together and pass beneath the inguinal ligament and inserts into the LESSER TROCHANTER of the femer

Question 5

How far (vertically) does the psoas major muscle span?

Answer 5

Runs from the lower end of T12 to the upper edge of L5

Question 6

The Psoas Major can be considered a major landmark for the posterior abdominal wall. Why is this so?

Answer 6

• The lumbar plexus is WITHIN psoas major
• The lumbar vessels run BEHIND psoas major
• The Sympathetic trunk, ureter and psoas minor are IN FRONT

Question 7

What is one of the major functions of the psoas major muscle?

Answer 7

It is an important flexor of the vertebral column (it is weakened in lordosis)
= maintains an erect spine

Question 8

In what proportion of people does the psoas minor exist in?

Answer 8

In about 2/3 of people - it is phylogenetically degenerating muscle disappearing from the species: doesn’t have many functions

Question 9

What is the structure of the psoas minor muscle? Where does it insert to?

Answer 9

It is a short, slim belly of muscle and a long and slender tendon on the surface of the psoas major muscle.

It has no real insertion, it blends with the periostium of the pelvis and petters out from there.

Question 10

Where does the quadratus lumborum sit? And where does it attach to?

Answer 10

Superolaterally (above) the psoas major muscle.

It attaches to the 12th rib above,
to the tips of the transverse processes,
To the posterior half of the ileac crest below

Question 11

What are the major functions of quadratus lumborum?

Answer 11

It stabilises the 12th rib

It acts as a lateral flexor

Question 12

Where does the iliacus muscle sit? What is its shape?

Answer 12

Inferior and lateral to the psoas major muscle.

It is an inverted triangle shape

Question 13

Where does the iliacus muscle attach?

Answer 13

The ilieac bone of the pelvis has a smooth fossa on the internal surface - origin of the iliacus muscle.

It runs edge to edge with psoas major and its fibres converge and pass beneath the inguinal ligament and into the lesser trochanter of the femur

Question 14

What is important about the relationship between psoas muscle and the ilacus muscle?

Answer 14

They both converge beneath the inguinal ligament into the lesser trochanter of the femur by a COJOINED TENDON called the ILIOPSOAS TENDON

Question 15

What is each muscle of the posterior wall enclosed by and why?

Answer 15

A dense fascia for firm fixation for the peritoneum

Question 16

What two muscles of the posterior abdominal wall have their own fascia surrounding them?

Answer 16

Psoas Major

Iliacus

Question 17

What is the thoracolumbar fascia? What is it made up of?

Answer 17

A complex fascia that has THREE DENSE fascial layers (tri-laminar structure) made up of a tough fibrous tissue

1. Posterior: attached to the tip of the spinous process
2. Middle: attached to the tip of the transverse process
3. Anterior: attached to the anterior surface of the transverse process

Question 18

What are the two compartments of the thoracolumbar fascia? What makes them and what is contained in them?

Answer 18

The quadratus lumborum is enclosed in the anterior compartment (made by the middle and anterior layers)

The erector spinae muscle is enclosed in the posterior compartment (made by the middle and posterior layer)

Question 19

What is different about the posterior layer of the fascia?

Answer 19

The posterior lamina/fascia extends the whole extent of the erector spinae muscle - from cervical to sacrum

Question 20

What is important about the line of fusion of these three layers of the fascia?

Answer 20

All the layers fuse laterally along the line/tip of the 12th rib.
It is a strong vertical fascial structure that gives attachment to the anterior abdominal walls (anchoring transversus abdominas and internal oblique)
(note: external oblique doesn’t attach here because the latissimus dorsi intervenes: instead has a free posterior edge)

Question 21

What is a psoas abscess? How is this relevant to applied anatomy?

Answer 21

Tuberculosis can present as TB osteomyeitis affecting the vertebral processes. When this occurs in the lumbar spine, the caseous necrosis can break through boney cortex and erupt into the psoas muscle causing a psoas abscess.

But because the fascia is so dense surrounding the psoas, the necrotic tissue is retained in the fascia and tracked down into the groin and presents as a lump in the groin (not in the muscle)

Question 22

Describe the peritoneum

Answer 22

Parietal layer lining the walls of the abdominal cavity
From various points on the posterior wall, the layer reflects off back to form a series of double layer folds lining the organs = visceral peritoneum

Together these form the MESENTERY

Question 23

What is the difference between intra- and retro-peritoneal?

Answer 23

Intraperitoneal structures are completely surrounded by peritoneum while retroperitoneal (eg. kidney) have their backs on the posterior abdominal surface and the peritoneum reflects off their anterior surface

Question 24

Describe the position of the kidneys

Answer 24

Lateral to the vertebral column in the paravertebral gutters
They lie on top (anterior to) the quadratus lumborum muscle
The are classically described as spanning from T12 to L3
Their superior tips lie anterior to the 12th rib
The right kidney is always slightly lower than the left (liver pushes it down)

Question 25

Why is the exact vertical location of the kidneys not definable?

Answer 25

Because they are not static: they move on respiration because they are intimately related to the diaphragm

Question 26

How can anatomy be applied to surgical access to the kidneys?

Answer 26

The anterior approach to the kidneys requires moving through all the structures of the anterior abdominal wall and the peritoneal cavity. It is not ideal to enter the peritoneal cavity uncessesarily = fibrination and scar tissue formation.
- some surgeous overcome this by tunneling past it

Posterior (or lateral) access means that only simple structures need to be passed and access to the kidneys is easy without interference with the peritoneal cavity (sometimes requires removing the 12th and 11th rib)

Question 27

Describe the kidney

Answer 27

Reddish brown, kidney-bean shaped organs

10cm long x 5cm wide x 2.5cm thick

Question 28

Describe the associated adrenal glands of the kidney

Answer 28

Superior aspect of each kidney which are asymmetrical

RIGHT: pyramidal shape at the apex
LEFT: crescent shape associated with the upper pole (wraps down onto the medial surface)

Question 29

The kidneys are solid viscous organs. What is meant by this?

Answer 29

They are composed of clusters of secretory cells
They are divided into cortex and medulla
They are enveloped by a fibrous capsule

Question 30

What is perinephic (or perirenal) fat?

Answer 30

A thick layer of fat which is enclosed by renal fascia surrounding the kidneys

Question 31

Describe the organisation of the kidney cells (cortex vs. medulla)

Answer 31

The outer cortex is pale and continuous. It completely surrounds the renal medulla.

The medulla is discontinuous and interior to the cortex. It is darker tissue and triangle shaped (apex towards the hilum) - called medullary or renal pyramids

Question 32

What surrounds the ducts, vein and artery of the kidney?

Answer 32

They are embedded in fat in a space continuous with the hilum called the RENAL SINUS

Question 33

Which direction does the hilum face? What runs through the hilum and in what order?

Answer 33

The hilum faces anteromedially

from front to back): vein, artery, duct (ureter
also has nerves and lymphatics scattered throughout

Question 34

Describe the blood supply to the kidneys

Answer 34

There is a SINGLE large renal artery that exits as a lateral branch of the abdominal aorta. Once it enters the hilum it divides into 5 segmental arteries supplying a functional segment of the kidney.

There is sometimes an accessory renal artery seen either going independently into the kidney in the hilum or elsewhere.

Question 35

What is the difference between left and right renal arteries?

Answer 35

The left renal artery comes straight out of the abdominal aorta and into the left kidney

The right renal artery passes behind the IVC and into the right kidney

Question 36

Describe the venous drainage from the kidneys. What is the difference between left and right renal veins?

Answer 36

Multiple, segmented renal veins unit at the hilum to form a single renal vein
The right plugs straight into the left IVC
The left renal vein crosses in front of the abdominal aorta and enters the left of the IVC

Question 37

How does the development of the kidney affect its blood supply?

Answer 37

The kidneys start sitting low on the posterior abdominal wall and because of differential growth rates, they look like they rise up the wall.
As it changes it also changes blood supply (looses its lower supply and gains a new higher one)

Question 38

What is the ureteric pelvis?

Answer 38

Also called the renal pelvis
The dilated upper part of the ureter (beginning of the ureter)
- the most posterior structure in the hilum (the duct)
- flat, funnel shaped expansion of the upper ureter sitting in the renal sinus (embedded in fat)

Question 39

What does the ureteric pelvis receive?

Answer 39

It receives from three major calyces which in turn receive from 2-3 minor calyces which recieve from the downward pointing pyramid of the medulla= CALYCEAL SYSTEM

Question 40

What are the ureters?

Answer 40

Muscular tubes that transport urine from the kidney into the bladder.
About 25-30cm long

Question 41

Describe the path of the ureters

Answer 41

They descend on the posterior abdominal wall structures overlying the psoas major muscle.

• The vertical descent corresponds to the tips of the lumbar transverse processes.(The abdominal course from the hilum of the kidney to the pelvic rim tracks down the lumbar processes)
• They tip over the pelvic rim into the pelvis, run along the side wall of the pelvis before turning and entering the base of the bladder

Question 42

What is the blood supply of the ureters?

Answer 42

Because they transverse a long course, they take blood supply from whatever they are passing by (ie. have a multi-level blood supply)

There is no ureteric artery

Question 43

What are the narrowings of the ureters?

Answer 43

1. in the beginning (ureteric pelvis to the start of the the ureter)
2. at the end (penetration into the bladder)
3. kinked as it passes over the pelvic rim

These are major sites for stones lodging

Question 44

What is urinary regurgitation, why would it occur? How is the body protected from it?

Answer 44

Urinary flow is down a downward pressure gradient. When urinating, the bladder contracts and there is propensity of regurgitation of urine back into the ureter.
The oblique course of the tubes prevents this.
A sphincter also closes the distal end