Collateral circulation Flashcards
How much cardiac output supplies the brain?
15%
How much of the flow from the CCA enters the normal ICA?
80%
brain has what ____ metabolic rate?
High metabolic rate (little circulatory reserve)
The brain is entirely dependent on what?
On the vascular system
Short episodes of interrupted cerebral flow can bring on symptoms of what?
Cerebral dysfunction
Cellular death can occur in how many minutes?
3-8 mins
Resistance is affected by what? (2)
- length of vessel
2. width of vessel
Whats more limiting width or length?
width because of poiseuille’s law
Adequate arterial perfusion relies on? (3)
- systemic blood pressure
- cardiac output
- blood volume
If circulation is compromised by atherosclerotic disease compensation may be insufficient and lead to?
Regional or diffuse hypoxia or anoxia
collateralization testing thats available? (4)
Duplex ultrasound
Angiography
MRI angiography-MRA
CT angiography-CTA
collateralization testing thats available? (4)
Duplex ultrasound
Angiography
MRI angiography-MRA
CT angiography-CTA
How long does it take for collaterals to develop?
- over a period of many years
- May patients don’t reveal any symptoms of cerebrovascular disease even with total occlusion of both ICA’s
why does collateral circulation develop?
change in the pressure gradient between the vessels, caused by a stenosis
Collateral pathway is dependent on what (2)?
- patient age
- time sequence of occlusion
- In older individuals, collateral pathways may already be hypoplastic or atherosclerotic
3 major collateral routes?
- Other side of the circle of Willis
- The posterior cerebral circulation
- The external carotid artery branches
what % of patients have a complete circle of willis?
50%
potential collateral in an occluded left ICA? (Other side of circle of willis)
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
potential collateral in an occluded left ICA? (Posterior circulation)
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
potential collateral in an occluded left ICA? (ECA branches)
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
Why is knowledge of the peri-orbital circulation is necessary?
- Its next to the circle of willis
What is the 2nd most important source of collateral flow?
the anastomosis between branches of the ECA and the ICA via the orbital and ophthalmic arteries
Flow into the orbit is normally via?
the ophthalmic artery
What is the only branch of the ICA to give off branches that leave the intracranial space?
opthalmic artery
peri-orbital branches from the ICE include? (3)
- frontal arteries
- supraorbital arteries
- nasal artery
periorbital branches of the ICA can communicate with branches of? Why is this important?
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
What collateralization is second to the circle of willis?
- The complex intracranial-extracranial anastomoses: between external and internal carotids
- Via the Orbital (ECA branch) and Ophthalmic (ICA branch) arteries
Branches of the intracranial-extracranial anastomoses? (6)
Lacrimal Supraorbital Anterior and posterior ethmoidal Medial palpebral Frontal Dorsal nasal artery
When an occlusion occurs in the ICA what happens to peri-orbital circulation?
flow in the ophthalmic artery becomes retrograde in order to supply the brain
3 less important collateral possibilities
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
CCA occlusion- ECA to ICA collateralization?
- Flow reverses in the ECA and flows into the ICA in the opposite direction towards the brain
