Brain Vasculature & Cerebrospinal Fluid

• The following are study notes on the Arterial and Venous Vasculature of the brain, Cerebrovascular Accidents (CVA), Blood Brain Barrier and Cerebral Spinal Fluid (CSF)

Arterial Vasculature

• The cerebral arterial system is divided into the vertebral and basilar arteries and the internal carotid arteries.
• The cerebellar, cerebral, spinal and pontine are all arteries included in the vertebral and basilar arteries of the brain.
• Cerebral arteries are included in the internal carotid arteries.
• Circle of Willis provides an anastomosis, that provides an alternate route for blood, in case one route is blocked.
• Vertebral and Basilar arteries include the posterior cerebral artery (PCA), superior cerebellar artery (SCA), anterior inferior cerebellar artery (AICA), posterior inferior cerebellar artery (PICA), and anterior and posterior spinal arteries

Circle of Willis

• Internal Carotid artery includes the posterior communicating artery, middle cerebral artery (MCA), anterior communicating artery, anterior cerebral artery (ACA) and ophthalmic artery
• Pontine and internal auditory arteries are also components of the the Circle

Internal Carotid System

• The internal carotid system consists of the internal carotid, ophthalmic, posterior communicating, anterior communicating, anterior cerebral (A1, A2), 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) arteries.

Latex Filled Vasculature

• Anterior communicating artery in the brain connects the Anterior cerebral artery (ACA) to the brain
• A1 segment ACA, and the M1 segment MCA are large cerebral arteries
• Superior Cerebellar Artery, AICA and PICA make up the the blood supply of the posterior brain structures

Examples of CVA

• CVA can be caused by aneurysms, atherosclerosis, dissection, arterio-venous malformations, infarction and ischemia

Atherosclerosis

• Atherosclerosis at bifurcations of major vessels in the Circle of Willis
• Atherosclerosis, inside the circle, enables anastomosis for collateral supply
• Basilar artery has no collateral perfusion

Risk Factors of CVA

• Risk Factors that could cause Atherosclerosis are occlusive stroke, and eventually infarction, hemorrhage
• Aneurysm, dissection, hemorrhage, infarction cause tissue death

Internal Vascular Supply

• Basal ganglia, hippocampus and posterior limb of internal capsule supplied by anterior choroidal artery.
• Basal ganglia and the posterior limb of internal capsule are supplied by lenticulostriate arteries, coming off of the M1 proximal branch of MCA
• Basal ganglia, limbic structures, and anterior limb of internal capsule supplied by the recurrent artery of Heubner, a penetrating branch coming off the proximal ACA
• The thalamus and posterior limb of internal capsule is suplied by the thalamoperforator, thalamogeniculate and posterior choroidal

Stroke Symptoms

• Occlusion of lenticulo-striate branches off left M1 segment into internal capsule

Midline Cortical Supply

• The midline cortical supply is the area perfused by the ACA and PCA
• Calloso-marginal and peri-callosal artery, medial temporal, occipital are supplied by the ACA, and PCA

External Cortical Supply

• Antero-medial frontal lobe gets supply from ACA
• Lateral frontal, parietal, temporal lobe gets supply from MCA (M3 superior, M4 inferior)
• Parietal, inferior temporal, occipital gets supply from PCA

Global cerebral ischemia

• Global cerebral ischemia is a diffuse state of hypoxia or ischemia throughout the brain and can be caused by cardiac arrest, shock, and hypo-perfusion

Focal Cerebral Ischemia

• This ischemia is local and specifically caused occlusion from embolism, thrombus or vasculitis.

Intra-Cerebral Hemorrhage

• This hemorrhage occurs in lacunar infarctions and Charcot-Bouchard micro-aneurysms
• Penetrating arteries to the thalamus, basal ganglia and internal capsule are end arteries, meaning there is no anastomosis and no collateral perfusion

Small Lacunes

• Lacunes in the posterior limb of the internal capsule cause pure hemi-paresis with descending motor issues and no sensory loss
• Lacunes in the ventral posterior nucleus of the thalamus cause pure hemi-sensory loss (ALS or DCML) with ascending sensory issues
• Etat lacunaire causes progressive dementia, cranial nerve palsies, dysarthria, dysphagia, (+) gag reflex, emotional imbalance

Venous System Drainage

• Superficial, Deep Veins, Internal Cerebral Veins, Basal Veins of Rosenthal drain into Internal Jugular Vein

Superficial Veins

• Superficial veins drain into the superior sagittal and cavernous sinuses.

Deep Veins

• Deep veins drain into the Great Vein of Galen

Blood Brain Barrier (BBB)

• Astrocytes induce endothelial tight junctions / BBB.
• Metabolic barrier - MAO.
• Pericytes maintain the BBB

Exchange from Blood or Brain/CSF: -

• Lipid soluble diffusion
• Receptor mediated transport
• Ion channel diffusion

Cerebral Spinal Fluid (CSF)

• CSF are functions as a shock absorber
• Are involved in removal of metabolites
• Work as pH buffer

Blood CSF Barrier

• Capillary filtration
• Active epithelial transport
• Low in protein, low in ionic. Increased CSF protein: meningitis
• Appearance of RBCs occur due to Infarction, Infection

Getting Dopamine into Brain

• Oral L-DOPA crosses the blood brain barrier
• Combine with carbidopa to decrease L-DOPA metabolism.
• L-DOPA converted to Dopamine