Part 9: Posterior Abdominal Wall

Question 1

Describe the layout of posterior abdominal wall with major muscles and vessels

Answer 1

5 vertebrae (L1-5) which project forward creating convexity. IVC and Aorta lie in front of vertebrae. Paravertebral muscles lie each side floored by psoas and quadratus lumborum muscle

Question 2

What is the origin, insertion, action and innervation of Psoas Major muscle?

Answer 2

O: Transverse process L1-5 and bodies T12-L5 and intervertebral discs T12-L4
I: Middle surface of LT of femur
A: Flexes hip, aids inflexion of abdomen
N: Anterior primary rami of L1,2

Question 3

What is the origin, insertion, action and innervation of Psoas Minor muscle?

Answer 3

Only occurs in 2/3 of people
O: Bodies T12-L1 and intervening vertebral discs
I: Pectineal line of pubis and fascia over iliopsoas
A: Weak flexor of trunk
N: Anterior primary rami of L1

Question 4

What is the origin, insertion, action and innervation of Quadratus Lumborum muscle?

Answer 4

O: Inferior border 12th rib
I: Apicis of transverse process L1-4, iliolumbar ligament and posterior 1/3 of iliac crest
A: Fixes 12th rib during respiration, laterally flexes trunk
N: Anterior primary rami T12-L3

Question 5

What is the origin, insertion, action and innervation of Iliacus muscle?

Answer 5

O: Iliac fossa within abdomen
I: Lowermost surface of LT of femur
A: Flexes hiip
N: Femoral nerve in abdomen (L2,3)

Question 6

What are the 3 significant fascia’s of the posterior abdominal wall?

Answer 6

Psoas fascia, Iliac fascia and thoracolumbar fascia

Question 7

Where is psoas fascia?

Answer 7

Invests surface of psoas muscle, attached to vertebra bodies, fibrous arches and transverse process. Retains pus of a psoas abscess. Thickening of psoas fascia from body of L1 vertebra to transverse process is medial arcuate ligament.
Is continuation of iliac fascia

Question 8

What is the iliac fascia?

Answer 8

Covers iliac muscle. Attached to bone at margins of muscle and to inguinal ligament. Forms floor of abdomen, attachment for parietal peritoneum. Does not extend into thigh.

Question 9

What is lumbar fascia?

Answer 9

Lumbar part of thoracolumbar fascia.
3 parts - anterior: occupied by quadratus lumborum, extends from root of transverse process to blend with middle fascia along lateral quadratus fascia margin
Middle: Tips transverse process to blend with both anterior and posterior layers laterally along line of erector spinae
Posterior: occupied by erector spinae, from spinous process to blend laterally. Extends up into thorax (only layer to do so) ending at 1st rib

Question 10

Describe the path of abdominal aorta?

Answer 10

Enters abdomen behind median arcuate ligament at T12. Passes slightly to left. Bifurcates at L4.

Question 11

How can the branches of AA be classified?

Answer 11

Single ventral branches to gut (Coeliac, SMA, IMA and median sacral)
Paired branches to abdominal wall (subcostal, inferior phrenic, lumbar arteries) and paired branches to other viscera (suprarenal, renal and gonadal)

Question 12

What crosses aorta between CT and SMA?

Answer 12

splenic vein and body of pancreas

Question 13

What crosses aorta between SMA and IMA?

Answer 13

L renal vein, duodenum (D3) and uncinate process of pancreas

Question 14

What levels do suprarenal, renal and gonadal arteries branch? Where do they run?

Answer 14

suprarenal: roughly L1, R runs across the crus of diaphragm, across IVC and bare area of liver, L behind post wall of lesser sac. both to suprarenal glands
Renal: L2
R - longer, crosses crus, psoas and behind IVC to hilum
L - shorter, crosses crus and psoas
Gonadal: Just below renal, above IMA.
Sweep down over psoas, cross ureter and supply middle 1/3. Crossed by colic vessels. Reach pelvis halfway between SI joint and inguinal ligament. From there male passes along brim to enter deep inguinal ring, female crosses pelvic brim and enters suspensory ligament

Question 15

Does ureter go over or under iliac bifurcation?

Answer 15

Over at point of iliac bifurcation into internal and external arteries

Question 16

There is no 5th lumbar artery as aorta bifurcates at L4 - what takes its place?

Answer 16

Iliolumbar artery - branch from internal iliac

Question 17

What is the surface marking for common and external iliac artery bifurcation?

Answer 17

Aortic bifurcation is just left of midline level with highest point iliac crest. Iliac’s follow slightly concave line laterally to midpoint between ASIS and pubic symphysis. Bifurcation occurs 3cm along this line.

Question 18

What are the branches of external iliac artery?

Answer 18

Inferior epigastric and deep circumflex iliac artery

Question 19

Describe the course of IVC

Answer 19

Begins at confluence of common iliac’s at L5 slightly to R of vertebrae. Runs up on R side of aorta. Exits abdomen through central tendon at T8.

Question 20

What is the surface marking of the course of IVC?

Answer 20

Point 2.5cm to R of intertubercular plane to point 2.5cm to R xiphisternum

Question 21

What are the tributaries to the IVC?

Answer 21

No analogous with veins.
Hepatic veins (portal system) - usually 3
Common iliac
Lumbar veins
Gonadal veins
Renal veins
R lumbar azygous vein
Right suprarenal vein
inferior phrenic veins

Question 22

Which pairs of veins only have one pair enter IVC?

Answer 22

Gonadal - L usually drains to L renal
L suprarenal to L renal
L lumbar azygous - often to hemiazygous

Question 23

Describe the venous drainage of the lumbar vessels

Answer 23

3+4 drain into IVC
1+2 join ascending lumbar vein which unites common iliac vein and iliolumbar vein passing vertically up to form azygous and hemiazygous veins

Question 24

What is the lymph drainage of the posterior abdominal wall?

Answer 24

Alimentary tract (liver, gallbladder, biliary tree, spleen, pancreas) drain to pre-aortic nodes via arteries.
Lymph drains via paired arteries to para-aortic nodes.
This all drains to cisterna chyli which is formed under cover of R crus in front of L1 and L2

Question 25

The lumbar plexus is formed from what nerve roots?

Answer 25

L1-4

Question 26

What nerve roots supply sensation to abdominal wall?

Answer 26

T12 and L1

Question 27

Where does subcostal nerve arise and where does it innervate?

Answer 27

T12 - passes down through lateral arcuate ligament into abdomen passes laterally, pierces TAM to lie in NVP supplying lower rectus abdominis, pyramidalis and lateral cutaneous branch to skin of anterior buttock

Question 28

Where does iliohypogastric nerve arise and where does it innervate?

Answer 28

L1.
Lie on QL. Lateral cutaneous branch to skin of upper buttock and then passes above superficial ring IC to supply skin over lower rectus abdominus and mons pubis

Question 29

Where does ilioinguinal nerve arise and where does it innervate?

Answer 29

L1, collateral branch of iliohypogastric.
Runs on QL. Enters inguinal canal from side, becomes covered in spermatic fascia at superficial ring. Supplies anterior 1/3 scrotum/labium majora and root of penis/clitoris

Question 30

Where does lateral femoral cutaneous nerve arise and where does it innervate?

Answer 30

L2,3 - posterior divisions.
Emerges lateral border passing on iliacus and then below inguinal ligament into thigh to supply lateral thigh. Supplies parietal peritoneum of iliac fossa

Question 31

Where does femoral nerve arise and where does it innervate?

Answer 31

Posterior divisions of anterior rami L2,3,4.

Runs deep in gutter between psoas and iliacus. Enters thigh by passing below inguinal ligament lateral to femoral sheath

Question 32

Where does genitofemoral nerve arise and where does it innervate?

Answer 32

L1,2. Emerges from anterior surface, runs down psoas muscle. L nerve overlaid by ureter, gonadal vessel, L inferior colic a.
R overlaid by ureter, gonadal vessels and ileocolic. Divides into genital and femoral branches. Genital to spermatic cord, supplies cremaster muscle. Femoral in front of femoral artery to supply skin in groin below IL

Question 33

What is the sympathetic nervous supply of the abdomen?

Answer 33

From lumbar sympathetic trunk and coeliac plexus. Lumbar trunk supplies pelvic viscera and somatic branches.
Coeliac plexus is entirely visceral, including gonads. Suprarenals have second supply direct from splanchnic nerves - for adrenaline production

Question 34

What is the parasympathetic supply of abdomen?

Answer 34

From

• Vagus nerve (both vagi contribute to coeliac plexus) - innervates to transverse colon
• Pelvic splanchnic nerves form inferior hypogastric plexus (S2,3,4) - arise from anterior rami of sacral nerves - innervates from splenic flexure to rectum