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In my talk, I will first briefly review the Anatomy and then,
the Physiology of the Cerebral Circulation and finish off with the basic Pathophysiology,
as it relates to cerebrovascular diseases.
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Arterial blood is supplied to the brain via the two internal carotid arteries,
and the two vertebral arteries,
the latter merging to form the basilar artery.
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At the base of the brain,
the internal carotid divides to form the anterior and the middle cerebral arteries,
abbreviated as ACA and MCA respectively,
and the basilar artery divides to form the two posterior cerebral arteries PCA.
However, one also finds an anterior communicating artery, ACom,
between the two ACAs and a posterior communicating artery,
PCom, between the ICA and PCA on each side.
As a result, the Circle of Willis is formed,
which allows the anterior and posterior systems,
as well as the right and left sides of the brain
to communicate in terms of arterial blood supply.
Hence, an occlusion of an artery proximal to the Circle of Willis can be
compensated for completely or partially by the remaining arteries.
However, about 50 percent of people have incomplete Circle of Willis.
These persons are at a higher risk of having
more serious strokes from proximal arterial occlusions.
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At the base of the brain,
the arteries of the Circle of Willis send out branches that run
perpendicularly to them and supply the basal ganglia,
thalamus, and deep, white matter.
Similar branches stem from the basilar artery to supply the brainstem.
These arteries are called the perforators.
They do not significantly anastamose and
therefore, their occlusion generally results in a lacunar infarct.
At the surface of the brain, the anterior, middle,
