2.5 Spinal Cord Blood Supply

Question 1

Describe the blood supply of the spinal cord.

Answer 1

The spinal cord derives its blood supply from a

1. Single anterior spinal artery (ASA),
2. Posterior spinal arteries (PSA), 2
3. Communicating segmental arteries
4. Pial plexus.

Question 2

ASA

Answer 2

Single artery formed at the foramen magnum

by the union of each vertebral artery.

Blood flows centrifugally supplying the

anterior two-thirds of the spinal cord

in front of the posterior grey column.

Question 3

PSA

Answer 3

Derived from the posterior inferior cerebellar artery (PICA)

or vertebral artery,

with blood flowing centripetally in this arterial system.

The arteries lie along the postero lateral surface

of the spinal cord medial to the posterior nerve roots.

Question 4

Pial arterial plexus

Answer 4

Surface vessels branch from the ASA and PSA

forming an anastomosing network that

penetrates and supplies the

outer portion of the spinal cord.

Question 5

segmental branches

Answer 5

Segmental or radicular branches

arise from various arteries—

vertebral, deep cervical,
costo cervical, aorta,
and the pelvic vessels.

Question 6

Arteria radicularis magna, or the artery of Adamkiewicz

Answer 6

Arises from the thoracolumbar part of the aorta,

usually on the left,

enters the spinal cord at the level of L1.

Question 7

Uniform blood supply?

Answer 7

Various regions of spinal cord are vascularised unevenly.

The cervical and lumbosacral parts
are well vascularised

whereas the thoracic part of the spinal cord,
especially the anterior region,

derives the branches from intercostal and iliac arteries,

which vary in location and numbers making it
prone to ischaemic damage.

See Figures 2.7 and 2.8.

Question 8

Describe the venous drainage.
What is its importance?

Answer 8

Radicular and spinal veins drain into

the internal vertebral venous plexus and
later drain into the azygos system
and the superior vena cava.

The plexus communicates with the basilar sinus
in the brain and with the pelvic veins
and inferior vena cava.

Question 9

Venous drainage. What is its importance?

Answer 9

So in patients with increased intra-abdominal pressure,

blood is diverted from the inferior vena cava to the plexus,

leading to engorgement of epidural veins.

a. This increases the risk of accidental venous puncture
during the conduct of epidural anaesthesia.

b. It also decreases the effective epidural space volume,
thereby requiring a smaller volume of local anaesthetic.

Question 10

Which part of the spinal cord
acts as a watershed zone?

Answer 10

Watershed effect occurs when

two streams of blood flowing in opposite directions meet.

This happens where the radicular artery unites with the ASA,

where blood courses upward and downward from the entry point,

thus leaving a watershed region

between the adjacent radicular areas where blood flows in neither direction.

-

The watershed effect is maximum in the
mid-thoracic area due to the greater
distance between the radicular arteries.

Question 11

What are the causes for poor
blood supply to the cord?

Answer 11

1. Trauma
2. Rupture of aortic aneurysm
3. Dissection of the aorta
4. Inflammation of aorta—vasculitis, collagen disorders
5. Venous hypertension
6. Degenerative spinal diseases and disc herniation
7. Severe atherosclerosis and luminal narrowing
8. Iatrogenic

Question 12

Iatrogenic

Answer 12

• Vasoconstrictors in epidural space
• Surgical cross clamping of the aorta
• Coeliac plexus block
• Deliberate/accidental hypotension

Question 13

What are the risk factors for spinal cord ischaemia during
aortic surgery?

Answer 13

According to recent statistics,
incidence of spinal cord ischaemia following
thoracoabdominal aortic aneurysm repair is 3% –18%

despite improved surgical technique, transfusion,
and perfusion technology.

The factors that determine the neurological outcome
after aortic cross clamping are:

__

1. Presence of predisposing factors,
   such as atherosclerosis, diabetes, and
   renal disease
2. Extent of aneurysm
3. Duration of cross clamp
4. Surgical difficulty
5. Previous aortic surgery
6. Severity of perioperative hypotension

Question 14

What are the different spinal cord protection strategies undertaken
during thoracoabdominal aneurysm repair?

Answer 14

1. Mild systemic hypothermia (32°–34°C):
2. Maintaining spinal cord perfusion pressure (SCPP)
3. Distal aortic shunting
4. Pharmacological neuroprotection:
5. Monitoring spinal cord function

Question 15

1. Mild systemic hypothermia (32°–34°C):

Answer 15

The most reliable protective adjunct and helps by
decreasing metabolic demands and attenuating
inflammatory response to ischaemia.

Question 16

2. Maintaining spinal cord perfusion pressure (SCPP)

Answer 16

Depends on the mean arterial pressure
and cerebrospinal fluid pressure (CSFP).

SCPP = MAP − CSFP

Cross-clamping leads to proximal hypertension

and increased cerebrospinal fluid pressure.

So controlling the arterial pressure with vasopressors
or decreasing CSFP via lumbar drains plays a significant
role in maintaining SCPP.

Question 17

3. Distal aortic shunting

Answer 17

Through femorofemoral bypass and left heart
bypass increases the blood flow to the distal aorta.

Question 18

4. Pharmacological neuroprotection:

Answer 18

Agents such as free radical scavengers,
barbiturates,
steroids,
opiate antagonists, etc.,

have been evaluated in decreasing the risk of ischaemic damage of the cord.

Question 19

5. Monitoring spinal cord function

Answer 19

with MEPs/SSEPs have proved effective
in preventing damage by avoiding important radicular arteries.

Question 20

What is AsA syndrome? What
are the findings?

Answer 20

ASA syndrome—problems in the anterior spinal artery territory resulting in
critical ischaemia of the anterior part of the spinal cord. The characteristic findings are

1. Motor
   Loss of motor function bilaterally below the level of lesion due to the
   involvement of corticospinal tracts
2. Sensory
   Loss of spinothalamic tracts resulting in bilateral thermoanaesthesia
   But intact light touch, vibration, and proprioception due to preservation of
   posterior columns
3. Autonomic
   Sexual dysfunction; loss of bladder and bowel function due to the effect on
   descending autonomic tract
   See Figure 2.9.