Fields et
al. described this in 1985. The actual pattern of collateral blood flow
depends on where the major vessels are stenosed or occluded and on which
collateral channels are available and free from disease.
On the whole,
the development of collateral channels is more effective if the major
vessel occlusion occurs over weeks or months rather than suddenly. Collateral
blood flow may develop via:
A. Extracranial connections:
-
In the
orbit, branches of ECA anastomose with branches of ophthalmic artery.
-
Branches
of ECA anastomose with branches of vertebral artery.
-
Branches
of vertebral artery anastomose with branches of subclavian artery.
-
Branches
of ECA anastomose with branches of subclavian artery.
B. Intracranial connections:
It is
a network of blood vessels present at the base of the brain. This
polygon of blood vessels is formed by the proximal parts of the two
anterior cerebral arteries connected by the ACoA and the proximal
parts of the two posterior cerebral arteries connected to the distal
internal carotid arteries by the posterior communicating arteries.
However fifty per cent of circles have hypoplastic or absent segments
and the potential for collateral flow is not always as good as it
might first appear.
It lies
on the surface of the brain. They develop between the cortical branches
of the anterior, middle and posterior cerebral arteries.
It occurs
between meningeal branches of the ICA, ECA and the vertebral arteries.
It is
a branch of ICA can anastomose with the
posterior choroidal artery
A branch
of ECA (Fields et al., 1985).
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