Posterior Abdominal Wall and Retroperitoneal Viscera

Question 1

What is the posterior abdominal wall made up of?

Answer 1

Psoas major muscle- a pair tucked in either side of the lumbar vertebral column.

• Quadratus lumborum is a quadrate muscle further lateral to the psoas major and above the iliacus muscle.
• Psoas minor muscle overlying psoas major but is absent in 1/3rd of people and present in 2/3rd.

Question 2

Describe the main features of the psoas major?

Answer 2

PSOAS MAJOR:

• Lies in the gutter bw the bodies and transverse processes of the lumbar vertebrae (overlying the transverse processes)
• Lateral border of psoas major is straight but oblique and very clearly line on plain abdominal X-ray.
• Has one continuous origin from the lower border of T12 to the upper border of L5, making it firmly anchored to the lumbar vertebral column between the bony thorax above and the bony pelvis below.
• Origin includes both the vertebral bodies and the intervening intervertebral discs. In addition, attaches from behind to the medial end of the transverse processes.
• Fibers converge, pass beneath the inguinal ligament to insert onto the lesser trochanter of the femur.
• Psoas is a useful organizer for deep structures of the posterior abdo wall. Lumbar vessels are behind it, lumbar plexus is within it and sympathetic trunk and ureter are in front of it.

Question 3

Describe the main features of the psoas minor?

Answer 3

PSOAS MINOR:
- Overlying psoas major, sits on the anterior surface. Short slender belly, long slender tendon. Muscle does not insert into bone, instead blends with the fascia overlying psoas and the periosteum of the pelvis.

Question 4

Describe the main features of the quadratus lumborum?

Answer 4

• Lying edge-to- edge with psoas major, beneath the 12th rib, above the posterior part of the iliac crest and along the tips of the lumbar transverse processes (hidden behind). Arises from the posterior part of the iliac crest and inserting into the inferior aspect of the 12th rib, therefore acts as a stabilizer of the 12th rib as well as lateral flexor of spine.

Question 5

Describe the main features of the iliac?

Answer 5

• Edge-to- edge with psoas. Beneath the quadratus lumborum, arising from the smooth iliac fossa on the anterior surface of the iliac bone (indicates that muscle overlying it). Fibres converge on the lateral border of psoas, pass beneath the inguinal ligament to insert via common conjoined tendon of iliopsoas to insert into the lesser trochanter of the femur.

Question 6

What is the fascia of the posterior abdominal wall?

Answer 6

• Psoas has its own fascia- psoas fascia and Iliacus has its own fascia- iliacus fascia.

Question 7

The thoracolumbar fascia gives attachment for which muscles?

Answer 7

The thoracolumbar fascia gives attachment to the TA and IO (but not EO) where its three layers fuse (go around to be anchored here). EO goes around but does not actually attach to anything- has a free posterior edge as well as free inferior edge (inguinal ligament) since it does not go around as far as the point of fusion of thoracolumbar fascia because latissimus dorsi intervenes.

Question 8

Where do the 3 layers of the thoracolumbar fascia arise from?

Answer 8

=Anterior layer comes from the front of the lumbar transverse processes and is anterior to the quadratus lumborum (not posterior as depicted in the slide above).
=Middle layer comes from the tip of the lumbar transverse processes (labeled as anterior layer in slide above).
=Posterior layer comes from the tip of the spinous processes.
- All three layers fuse at a line corresponding to the tip of the 12th rib, creating two compartments between the anterior and middle layer (anterior compartment) and between the middle and posterior layers (posterior compartment).
=Erector spinae muscles are contained within the posterior compartment of the thoracolumbar fascia- between the middle and posterior sheath.

Question 9

What is tuberculous/psoas abscess?

Answer 9

Tuberculous abscess in the lumbar vertebral body may eventually break through the outer cortex of the vertebral body and into psoas.

• Dense fascial envelope keeps abscess contained and so pus tracks down, contained by the psoas fascia, beneath the inguinal ligament and into the thigh.
• This leads to diffuse swelling and inflammation in the inguinal region/ thigh.

Question 10

What are intraperitoneal viscera?

Answer 10

Viscera that are completely surrounded by peritoneum and connected to abdominal wall by a double fold of peritoneum

Question 11

What are retroperitoneal viscera?

Answer 11

Some viscera, such as kidneys, lie in contact with the posterior abdominal wall behind the parietal peritoneum. Instead of the parietal peritoneum lining the posterior abdominal wall, line the front of the kidneys. Thus, structures that only have their anterior surface covered by peritoneum and have their back at the posterior abdominal wall

Question 12

What are classic features of the kidney? Shape, and I/R, location.

Answer 12

• Classic retroperitoneal viscus
• Kidneys sitting lateral to the vertebral column, in the paravertebral gutter.
• Abdominal cavity is kidney shaped, not an oval.
• Punching in of the vertebral column from behind creates two gutters either side of the vertebral column called the paravertebral gutters. - Kidneys sit either side of the vertebral column in the paravertebral gutters- almost behind the vertebral column.
• Tucked in adjacent to the vertebral column (vertebral bodies), overlying the transverse processes is the psoas and more lateral to this is quadratus lumborum, on which the kidneys sit within the paravertebral gutters.
• Part of the vertebral column that the kidneys are adjacent to are T12 to L3,

Question 13

What are the kidney’s location from the back? And as a result of their relationship to the diaphragm, what does this mean for their location?

Answer 13

• From behind they are anterior to the 12th rib and tucked immediately beneath the diaphragm.
• There relationship to the diaphragm means that they move down a bit with inspiration- some excursion in relationship to the vertebral column with breathing. This means that they are not always within T12 to L3.
• The liver on the right pushes the right kidney down slightly inferior to the left kidney.

Question 14

What are some ways a surgeon can reach the kidneys?

Answer 14

(1) Can make a para-median incision lateral to rectus abdominus and stay outside the peritoneal cavity and reach the kidney that way.
(2) More common are lumbar and lateral approaches, where the surgeon will resect the 12th rib and create a lumbar paravertebral incision to go straight into the retroperitoneal space, allowing beautiful access to the kidney without disturbing peritoneal contents.

Question 15

What is the size of the kidney?

Answer 15

Classically described as 10 cm long, 5 cm wide and 3.5 cm thick.

Question 16

What is the ‘party-hat’ shaped organ on top of the right kidney and the ‘crescent/half moon’ shaped organ on the left kidney?

Answer 16

• Adrenal glands are asymmetrical: right adrenal gland is a triangle/ pyramid sitting right on the superior aspect of the right kidney whereas the left adrenal gland is crescent shaped drops down a bit and sits supero-medial to the left kidney above the hilum.

Question 17

What are the features of a solid viscus?

Answer 17

• Classic solid viscera are made up of clusters of secretory cells.
  =Clusters of secretory cells organized into lobes and lobules or cortex and medulla (this is the case for kidney)
  =They will be enveloped by a capsule and typically additional covering (in abdo viscera/ kidney this is serosa)
  =Shape of solid viscus always bears the imprints of solid structures surrounding it.
  =Typically have borders and surfaces.
  =Always a hilum or slit where nerves and vessels and/or a duct enter and exit

Question 18

What is the kidney enclosed by?

Answer 18

-Kidney has its own fibrous capsule, which is surrounded by perirenal fat that is in turn enclosed by renal fascia.
=Can be quite a lot of fat surrounding the kidney in its capsule, making the kidney seem much larger than it is in reality.

Question 19

What is the cortex?

Answer 19

Outer part of the kidney, pale coloured, and a continuous band completely surrounding the medulla.

Question 20

What is the medulla?

Answer 20

Inner triangular shaped collections known as renal pyramids. Discontinuous darker coloured.

Question 21

Which way does the hilum of the kidney face, and where is it directed?

Answer 21

• Hilum/ vertical slit which faces medially but directed anteriomedially since kidneys sit almost behind the vertebral column and are certainly behind the aorta and IVC.

Question 22

In which way are the vessels situated on the kidney?

Answer 22

Renal vein (most anterior), renal artery and the renal pelvis/ dilated part of ureter (ureteric pelvis).

Question 23

What is the renal sinus?

Answer 23

A fat filled space that is continuous with the hilum, and the hillier structures are embedded in this fat.

Question 24

Which structure is the renal artery in the hilum?

Answer 24

Middle structure

Question 25

Where does the renal artery come off from?

Answer 25

Single, large renal artery coming off as a lateral branch of the abdominal aorta to enter the hilum of each kidney.

• Because the right kidney sits slightly lower than the left, the right renal artery comes off slightly lower than the left.
• In the abdomen, the IVC is to the right and the abdominal aorta is to the left.

Question 26

Vascular segments of the kidney are supplied by?

Answer 26

Each renal artery then divides into 5 segmental arteries, each of which go on to supply vascular segments of kidney.

Question 27

Where do kidneys start development, and what does this mean for their position?

Answer 27

Kidneys actually start their development in the pelvis. Differential growth rates means that it changes its position with respect to the posterior abdominal wall. It ascends the posterior abdominal wall, taking with its arterial supply successively and obliterating the lower blood supply when it takes the new one.

Question 28

Which structure is the renal vein in the hilum?

Answer 28

Most anterior.

Question 29

Where do the renal veins drain into?

Answer 29

Right and left renal veins drain into the IVC, which sits to the right of the abdominal aorta.

• This time the right renal vein has easy access- it is therefore short, horizontal and drains directly into the IVC.
• The left renal vein has to traverse the abdominal aorta by passing in front of it (avoiding compression) to drain to the IVC whereas right renal vein can drain directly into SVC.

Question 30

Which artery is the ONLY exception to the positioning of arteries and veins, and where is located?

Answer 30

Superior mesenteric artery.

It comes off the aorta, just above the left renal vein, and it overlies the vein.

Question 31

How many segments does the kidney have? How is it similar to the lung segments?

Answer 31

Each kidney is divided into 5 functional segments. Similar to the lung segments, they have their own arterial supply, their own venous drainage and their own ureteric drainage.

• Means that is one segment is affected, it will not interfere with the function of the rest of the kidneys segments.
• Surgeons exploit this and can tie off the arteries and veins to remove vascular renal segments.

Question 32

What is the ureter?

Answer 32

It is the flattened, funnel-shaped expansion of the superior end of the renal pelvis.

Question 33

What does the ureter transport and to where?

Answer 33

Urine into the ureter to be transported to bladder.

Question 34

What forms the renal pelvis?

Answer 34

2 or 3 major calyces unite to form the renal pelvis.

Question 35

What forms the major calyces?

Answer 35

Each of these major calyces are formed by the union of 2 or 3 minor calyces

Question 36

What do the minor calyces receive?

Answer 36

Each of the minor calyces recieves the point of the renal pyramid, the medullary loops and collecting ducts

Question 37

How is urine drained?

Answer 37

Urine draining draining via loop of Henle and collecting duct into the minor calycesàto the major calycesàrenal pelvisàureter.

Question 38

How does the ureter travel?

Answer 38

• Initial descent of the ureter on the posterior abdominal wall directly relates to psoas (overlying it).
• Muscular tubes that transmit urine to the bladder in a vertical descent which roughly corresponds to the tips of the lumbar transverse processes.
• Passes over the pelvic brim before running on the lateral wall of the pelvis and entering the bladder.

Question 39

Where can we look for kidney stones lodged in the ureter?

Answer 39

=Can look for radio-opaque kidney stones lodged into ureter as it is mapped along the tips of the lumbar trips of the transverse processes.

Question 40

Why is there no ureteric artery?

Answer 40

There is no ureteric artery because it receives its arterial supply from adjacent vessels down its course- some on the posterior abdominal wall, some on the pelvic brims, some in the pelvis.

Question 41

Why do we need to know the sites of narrowing?

Answer 41

Need to know the site of narrowing (a) likely area of where things to get lodged (b) if someone has tumour or sites of narrowing in the ureter, could misdiagnose something lodged in the site of narrowing as a tumour.

Question 42

Where are the sites of narrowing?

Answer 42

Always narrowing’s at the beginning and end.
First site (1) of narrowing is at the junction with the renal pelvis. Ureteropelvic junction [where renal pelvis narrows to become ureter]
Second(2) is where it crosses the iliac artery at the pelvic brim where kinking occurs.
Third(3) is passageway through the bladder wall. Uretero-vesical junction (at oblique passage through the bladder wall)