Collateral circulation

Question 1

How much cardiac output supplies the brain?

Answer 1

15%

Question 2

How much of the flow from the CCA enters the normal ICA?

Answer 2

80%

Question 3

brain has what ____ metabolic rate?

Answer 3

High metabolic rate (little circulatory reserve)

Question 4

The brain is entirely dependent on what?

Answer 4

On the vascular system

Question 5

Short episodes of interrupted cerebral flow can bring on symptoms of what?

Answer 5

Cerebral dysfunction

Question 6

Cellular death can occur in how many minutes?

Answer 6

3-8 mins

Question 7

Resistance is affected by what? (2)

Answer 7

1. length of vessel

2. width of vessel

Question 8

Whats more limiting width or length?

Answer 8

width because of poiseuille’s law

Question 9

Adequate arterial perfusion relies on? (3)

Answer 9

1. systemic blood pressure
2. cardiac output
3. blood volume

Question 10

If circulation is compromised by atherosclerotic disease compensation may be insufficient and lead to?

Answer 10

Regional or diffuse hypoxia or anoxia

Question 11

collateralization testing thats available? (4)

Answer 11

Duplex ultrasound
Angiography
MRI angiography-MRA
CT angiography-CTA

Question 11

collateralization testing thats available? (4)

Answer 11

Duplex ultrasound
Angiography
MRI angiography-MRA
CT angiography-CTA

Question 12

How long does it take for collaterals to develop?

Answer 12

• over a period of many years

- May patients don’t reveal any symptoms of cerebrovascular disease even with total occlusion of both ICA’s

Question 13

why does collateral circulation develop?

Answer 13

change in the pressure gradient between the vessels, caused by a stenosis

Question 14

Collateral pathway is dependent on what (2)?

Answer 14

1. patient age
2. time sequence of occlusion

• In older individuals, collateral pathways may already be hypoplastic or atherosclerotic

Question 15

3 major collateral routes?

Answer 15

1. Other side of the circle of Willis
2. The posterior cerebral circulation
3. The external carotid artery branches

Question 16

what % of patients have a complete circle of willis?

Answer 16

50%

Question 17

potential collateral in an occluded left ICA? (Other side of circle of willis)

Answer 17

Right CCA to right ICA to right ACA, across the anterior communicating artery ,then retrograde down the left ACA to the left MCA to perfuse the left hemisphere

Question 18

potential collateral in an occluded left ICA? (Posterior circulation)

Answer 18

Vertebral artery flow enters the basilar artery, to the left posterior cerebral artery, across the left posterior communicating artery to the distal left ICA and finally to the left MCA

Question 19

potential collateral in an occluded left ICA? (ECA branches)

Answer 19

The left ECA to an ECA branch (superficial temporal, maxillary or facial), retrograde down an ICA branch (supraorbital, nasal, or frontal) to continue retrograde flow down the ophthalmic artery, into the carotid siphon, and finally to the MCA to perfuse the left side of the brain

Question 20

Why is knowledge of the peri-orbital circulation is necessary?

Answer 20

• Its next to the circle of willis

Question 21

What is the 2nd most important source of collateral flow?

Answer 21

the anastomosis between branches of the ECA and the ICA via the orbital and ophthalmic arteries

Question 22

Flow into the orbit is normally via?

Answer 22

the ophthalmic artery

Question 23

What is the only branch of the ICA to give off branches that leave the intracranial space?

Answer 23

opthalmic artery

Question 24

peri-orbital branches from the ICE include? (3)

Answer 24

• frontal arteries
• supraorbital arteries
• nasal artery

Question 25

periorbital branches of the ICA can communicate with branches of? Why is this important?

Answer 25

communicate with the superficial temporal artery as well as the facial artery

This is importance in cases of severe obstruction or occlusion of the ICA

Question 26

What collateralization is second to the circle of willis?

Answer 26

• The complex intracranial-extracranial anastomoses: between external and internal carotids
• Via the Orbital (ECA branch) and Ophthalmic (ICA branch) arteries

Question 27

Branches of the intracranial-extracranial anastomoses? (6)

Answer 27

Lacrimal
Supraorbital
Anterior and posterior ethmoidal
Medial palpebral
Frontal  
Dorsal nasal artery

Question 28

When an occlusion occurs in the ICA what happens to peri-orbital circulation?

Answer 28

flow in the ophthalmic artery becomes retrograde in order to supply the brain

Question 29

3 less important collateral possibilities

Answer 29

1- the occipital branch of the ECA communicates with the atlantic branch of the vertebral artery
2-the deep cervical branch of the subclavian artery communicates with the more proximal branches of the vertebral artery
3-the “rete mirabile”consisting of a network of transdural arteries which may anastomose across the subdural space with the tiny arteries covering the surface of the brain

Question 30

CCA occlusion- ECA to ICA collateralization?

Answer 30

• Flow reverses in the ECA and flows into the ICA in the opposite direction towards the brain