Blood Supply

Allen Chung, class of 2013

Objectives• Understand the importance of the cerebral circulation.• Understand stroke and the types of vascular problems that cause it.• Understand ischemic penumbra and regulation of cerebral blood flow.• Describe the origin and distribution of the blood supply to the cerebral

hemispheres including the internal carotid, anterior cerebral, middle cerebral, posterior cerebral, and anterior choroidal arteries and the territories they supply.

• Be able to identify anterior, middle, and posterior cerebral arteries in lateral and anterior-posterior view angiograms.

• Describe the vessels associated with the Circle of Willis.• Describe the origin and distribution of the blood supply to the brainstem

including the territories supplied as shown in cross sections of brainstem.• Be able to draw the diagram of blood vessels (vertebral and carotid

supply to the Circle of Willis) on a figure of the brainstem.• Describe the origin and distribution of the blood supply to the spinal cord.• Describe the venous drainage for the hemispheres.

Why is Blood Supply ImportantBrain is very active metabolically

•Brain is 2% of body weight Uses 15% of cardiac output Consumes 20% of total available O2

•cerebral blood flow 750 ml/min cerebral blood volume 100 ml circulating blood turns over 7x/min

Chris Cohan, Ph.D.Dept. of PathologyUniversity at Buffalo

•Brain deprived of blood for • 20 sec – unconsciousness• 4-5 min – coma, irreversible

unconsciousness or death

•Some areas are more vulnerable to oxygen loss than others, eg Basal Ganglia, Hippocampus, Frontal Lobes

Why is Blood Supply Important

Why is Blood Supply ImportantStroke is the most common neurological

disorder!• 795,000 strokes each year in US• 140,000 deaths/yr from stroke• 3rd leading cause of death in US

• Stroke is the leading cause of serious, long-term disability

Why is Blood Supply Important•Consequences of lost blood supply are severe- loss of sensory, motor, and cognitive function.

•Increase in aging population, obesity, diabetes suggests cerebrovascular disease will continue to be a major problem.

Why is Blood Supply ImportantBlood vessels supply specific territories throughout the CNS. The pathway structures in these territories produce characteristic cluster of symptoms when blood supply is impaired. Knowledge of these pathways and territories is essential for understanding localization, interventions, and prognosis.

Examples of Territories

Infarct of MCA Ant Spinal Infarct

Infarcts cause focal deficits based on territories supplied by blood vessels

Clustering of symptoms

Stroke•Stroke – a syndrome caused by disruption of brain circulation; characterized by sudden onsetof neurological deficits lasting >24 hrsinvolving focal symptoms that correlate with a brain area supplied by the affected vessel.

Causes of Stroke

A. Ischemia 67%• TIA- transient ischemic attack• Infarction

1. Thrombosis2. Embolus

• Other: atherosclerosis, ¯ blood pressure, arteriovenous malformation

B. Hemorrhage 33%

Transient episode of neurological dysfunction caused by focal CNS ischemia without acute infarction.

.

Ischemic PenumbraSurrounding the core region of infarction is an impaired area of reduced blood flow- ischemic penumbra - which will eventually infarct if blood flow is not restored.

• Metabolic, electrical, and neurochemical processes are altered in the penumbra leading to impaired function.

• The infarcted area is damaged irreversibly, but the ischemic penumbra can be rescued in time-dependent manner.

• The infarcted area and the ischemic penumbra both contribute to the functional deficits of stroke.

• Goal of neuroprotection is to rescue the ischemic penumbra.

Pericytes Regulate Cerebral Blood Flow­ Neuronal activity ® ­ cerebral blood flow

• Basis of fMRI and most PET imaging• Neuronal activity causes Glu release from terminals. Glu

binds to NMDA receptors on pericytes surrounding brain capillaries, causing pericytes to relax, and a subsequent increase in diameter of capillaries.

• Ischemia causes pericytes to constrict, which reduces blood supply to the affected area. As pericytes die, they remain in a constricted state, reducing the possibility of restoring blood flow and leading to further neuronal death.

The origin and distribution of the blood supply to :1. Cerebral Hemispheres2. Brainstem3. Spinal Cord

Origin of Blood Supply1. Internal carotid arises from common carotid2. Vertebral arises from subclavian

Circle of Willis•Internal carotids and vertebrals anastomoze in the Circle of Willis

• Superficial branches supply the surface, penetrating branchessupply deep structures

Collateral circulation within the Circle of Willis occurs under some situations and can prevent infarction.

Origin of Blood Supply• Anterior: Internal carotids supply hemispheres and eye via:

• middle cerebral • anterior cerebral • anterior choroidal• ophthalmic artery

•Posterior: vertebrals supply hemispheres, brainstem, spinal cord, cerebellum:

• posterior cerebral• superior cerebellar• basilar• posterior inferior cerebellar• anterior inferior cerebellar• ant/post spinal

Anterior circulation

Posterior circulation

Post Cerebral Art

Ant Cerebral Art

Middle Cerebral Art

Anterior / Posterior Cerebrals

Post Cerebral Art

Ant Cerebral Art

Middle Cerebral

Middle Cerebral Art

Occlusion of specific branches results in symptom clusters

ICA

ACA

MCA

MCAACA

ICA

ACA

MCA

Lateral View Anterior-Posterior View

Lenticulostriate Arteries• Small, penetrating branches

of MCA supply– Putamen – Globus Pallidus

• Infarcts produce focal deficits

Lenticulostriate arteries

Other Structures Supplied•IC: eye (ophthalmic a.)

•ACA: corpus callosum

•Anterior choroidal: choroid plexus, hippocampus, amygdala, optic tract, lateral geniculate, Meyer’s loop, glob. pallidus, internal capsule

Deep StructuresInt.Cap IC, ACA, MCA, Ant

Chor, Post Comm

Caudate MCA, (ACA)PutamenGlobus Pall.

MCA via lenticulostriate, Ant Chor

Thalamus PCAHypothalamus PCA, Post Comm, ACA

coronal

PCA

ACA

MCA

Cerebellum:PICA, AICA, SCA

Supply to Brainstemanterior cerebral anterior communicating

posterior cerebral

middle cerebral

internal carotid

anterior choroidal

superior cerebellar

anterior inferior cerebellar

labyrinthine

anterior spinal

posterior spinal

posterior inferior cerebellar

vertebral

basilar

posterior communicating

Blood supply to the brainstem is crucial for function of sensory and motor pathways. Infarcts can have drastic consequences. To help you remember this blood vessel diagram, you will be required to draw it on the brainstem for exam 3.

Supply to Medulla

vertebral

anterior spinal

posterior spinal

anterior spinalvertebral

PICA

Supply to Pons

Basilar

paramedian

short circumferentials

long circumferentials

Overlapping supply: AICA, sup cerebellarOne or the other may supply this territory

basilar

Paramedian and circumferentials are general terms based on position or length. These are branches of the basilar artery.

Supply to Midbrain

Posterior cerebral

short circumferential

long circumferential

paramedianbranch of PCA

(or superior cerebellar)

basilar

posterior cerebral artery

The end of the basilar artery bifurcates into right and left posterior cerebral arteries.

Loss of blood supply for any branch will affect specific structures in the vessel’s territory.

1. specific sensory/motor symptoms

2. motor cranial nerve nuc/fibers can be in same territory as CST, causing alternating hemiplegia

3. cranial nerve symptoms indicate brainstem localization (not I, II, XI)

Supply to Spinal Cord

anterior and posterior spinal arteries are reinforced by radicular arteries.

Anterior spinal

Posterior spinal

Many feeder arteries = less vulnerable to infarct

Few feeder arteries = more vulnerable to infarct

Supply to Spinal CordPosterior spinal

Anterior spinal

Anterior Spinal ArteryAlternating branches to LT and RT. Blockage of a branch can cause infarct on one side of the spinal cord.

Venous System

Superficial/Deep cerebral veins

Dural venous sinuses

Internal Jugular vein

Blood vessels tutorials on the web site:• Territories and pathway structures• Angiograms

AND

• lesions localization tutorial on the Temple Univ web site (see link on Exams pg)