Cerebrovascular System and Accidents

Arterial Vasculature

• Arterial cerebro-vascular system includes vertebral and basilar arteries, internal carotid arteries, and the Circle of Willis
• Vertebral and basilar arteries supply cerebellar, cerebral, spinal, and pontine structures
• Internal carotid arteries specifically supply cerebral structures
• The Circle of Willis is an anastomosis of vessels ensuring collateral circulation

Cerebrovascular Accident (CVA) Examples

• CVA can result from aneurysms, atherosclerosis, dissection, arterio-venous malformations, infarction, and ischemia

Circle of Willis

• The vertebrobasilar system includes vertebral arteries and the basilar artery
• The vertebral and basilar artery are linked to the posterior cerebral, superior cerebellar, anterior inferior cerebellar, posterior inferior cerebellar, as well as anterior and posterior spinal arteries
• The internal carotid system involves the internal carotid artery
• Structures feed by the internal carotid are: posterior communicating, middle cerebral (MCA), anterior communicating, anterior cerebral (ACA), and ophthalmic arteries.

Internal Carotid System

• This system includes the internal carotid, ophthalmic, posterior communicating, anterior communicating, anterior cerebral (A1, A2 segments), middle cerebral (M1 proximal branch, M2 segments), lenticulostriate, and anterior choroidal arteries

Vertebro-Basilar System

• The vertebro-basilar system includes the vertebral, basilar, spinal, posterior inferior cerebellar, anterior inferior cerebellar, superior cerebellar, and posterior cerebral (P1, P2 segments) arteries

Vascular Supply

• Internal carotid provides blood to:
• Anterior choroidal (basal ganglia, hippocampus, posterior limb of internal capsule)
• M1 proximal branch of MCA (lenticulostriate arteries to basal ganglia, posterior limb of internal capsule)
• Proximal ACA (penetrating branches, recurrent artery of Heubner to basal ganglia, limbic structures, anterior limb of internal capsule)
• Basilar artery provides blood
• PCA (thalamoperforator, thalamogeniculate, posterior choroidal to thalamus and posterior limb of internal capsule)

Atherosclerosis

• Can occur at bifurcations of major vessels in the Circle of Willis
• Within the Circle, anastomosis provides collateral supply
• The basilar artery does not demonstrate collateral perfusion
• Can lead to occlusive stroke and/or infarction

Aneurysms

• May take the form of berry aneurysms at the base of the brain in the Circle of Willis
• Can also occur as micro-aneurysms within the cerebrum
• Can lead to hemorrhage and/or infraction

Infarction and Ischemia

• Ischemia indicates a lack of blood flow to a brain region
• Hypoxia represents a lack of oxygenated blood in a brain region
• Infarction signifies the death of brain parenchyma due to circulatory failure
• Occlusive stroke is thrombolytic or embolytic closure of a vessel
• Hemorrhagic stroke is the rupture of blood vessels

Global Cerebral Ischemia

• Presents as diffuse hypoxic or ischemic encephalopathy
• Signs - cardiac arrest, shock, and/or hypo-perfusion

Focal Cerebral Ischemia

• Characterized by occlusion caused by embolism, thrombus, or vasculitis

Intra-Cerebral Hemorrhage

• Also include lacunar infarction and Charcot-Bouchard micro-aneurysm
• Penetrating arteries to the thalamus, basal ganglia, and internal capsule are end arteries, and thus, do not have anastomosis or collateral perfusion

Lacunes

• Small lacunes that occur can be located in one if these positions
• Posterior limb of the internal capsule and cause pure hemi-paresis with descending motor loss
• Ventral posterior nucleus of the thalamus and cause pure hemi-sensory loss with ascending sensory loss
• Etat lacunaire represents progressive dementia, cranial nerve palsies, dysarthria, dysphagia, and emotional imbalance

Venous System

• Superficial veins include the superior sagittal and cavernous sinuses
• Deep veins include the great vein of Galen
• All veins eventually drain into the Internal Jugular Vein

Cerebrospinal Fluid and the Blood Brain Barrier

• Astrocytes induce endothelial tight junctions/BBB
• Pericytes maintain the BBB
• A metabolic barrier is present

Exchange from Blood/CSF/Brain

• Includes lipid-soluble diffusion, receptor-mediated transport, and ion channel diffusion

Functions of CSF

• Shock absorption, waste elimination, and pH regulation

Blood CSF Barrier

• Uses capillary filtration and active epithelial transport

CSF Characteristics/Indications

• Has low protein and low ionic properties
• Increased protein may be related to meningitis
• Appearance of RBCs is an indication of infarction or infection

Dopamine and Parkinson's

• Treatments involve using oral L-DOPA
• Combine Oral L-Dopa with Carbidopa to lower the metabolism levels
• L-Dopa is needed to convert to Dopamine