Cerebral Blood Supply

Describe the Sources of blood to the brain

Blood Supply to Brain:

• Two Sources: Internal Carotid + vertebrobasilar system.

  • joins together via communicating arteries in circle of Willis on base of brain.

  • allow collateral circulation

1. Describe the pathway of the ICA

2. Describe its first branches

Pathway of ICA:

• ascends from bifurcation → petrous portion via carotid canal → cartilage filled foramen lacerum → Cavernous sinus → travels anteriorly alongside sphenoid → ascends medial to anterior clinoid process → pierces through dural roof of sinus to become cerebral part → arches back below optic nerve → bifurcates @ anterior perforated substance → forms ant./mid cerebral arteries

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Branches:

• No major branches are given off from petrous part

• first branches associated w/ brain are in cavernous sinus to supply hypophysis and meninges.

Describe the hypophyseal arteries:

• Branches of?

• Supplies?

• Branches?

Hypophyseal arteries:

• Branches of ICA;

• supplies pituitary gland and part of the infundibulum

• Branches:

  • Inferior: arises in cavernous sinus

  • Superior: arises from the cerebral (supraclinoid) part

List the initial branches of the ICA

Initial Branches:

• Ophthalmic artery

• Posterior communicatinq artery

• Anterior choroidal artery

• Superior hypophyseal artery

Describe the ophthalmic artery

• Pathway

• Supply

• Important Branch?

• Clinical Importance?

ophthalmic artery

• Pathway

  • enters orbit via optic canal → multiple branches

• Supply:

  • eye + extraocular structures of orbit

• Important Branch: Central artery of Retina:

  • critical for visual function

  • enters optic nerve as it approaches eyeball and supplies the retina.

• Clinical Importance:

  • can carry small particles (microemboli) from carotid →

    • ransient or permanent visual loss

    • appearance of small ischemic areas visualized on retina

  • This is b/c ophthalmic artery arises early from ICA

Describe the posterior communicating artery

• Pathway

• STATs

PCA:

• Pathway:

  • travels over oculomotor nerve in posteromedial direction → joins w/ posterior cerebral artery,

    • connects carotid w/ vertebrobasilar system

• STATs:

  • size of this artery varies greatly

  • may be absent in small percentage of individuals

describe the anterior chordal artery

• Pathway/Supply

• Branches

• Clinical Importance

AchA:

• Pathway/Supply:

  • follows optic tract in caudal/lateral direction around crus cerebri → @ lateral geniculate body, branches → branches enter inferior horn of lateral ventricle via choroidal fissure → supply choroid plexus.

• Branches:

  • to optic tract

  • crus cerebri,

  • amygdala,

  • anterior hippocampus,

  • tail of the caudate,

  • medial globus pallidus,

  • posterior limb of the internal capsule (ventral portion),

  • retrolenticular limb of intemal capsule.

  • lateral thalamus (including LGB),

• CLINICAL IMPORTANCE:

  • damage = consistant w/ damage to posterior limb of int. capsule:

    • Hemiplegia

    • Hemianesthesia

    • Hemianopsia

    • NOTE: visual field defects are a variable feature and if present, may be transient.

List the terminal branches of the ICA

Terminal Branches:

• Anterior Cerebral

• Middle Cerebral

Describe the anterior cerebral artery

• Pathway

• Branches

• Supplies

• Clinical Importance

Anterior Cerebral Artery

• Pathway:

  • runs medially over optic chiasm to near midline position → joined by contralateral counterpart via anterior communicatinq artery near cistern of lamina terminalis

  • Branches extend dorsolaterally onto lateral surface of the hemisphere

• Branches:

  • orbitofrontal,

  • frontopolar,

  • callosomarqinal

  • pericallosal artery.

• Supplies:

  • Paracentral Lobule

    • Contains cortical centers for movement and sensation of the lower limb

  • Ventromedial Prefrontal Cortex

    • Important for executive functions including decision making and planning

• Clinical Importance:

  • symptoms depends on which branch is occluded:

    • Paralysis of opposite foot and leg — UMN lesion

    • Sensory deficits over toes, foot, and leg

    • Cognitive impairments

      • planning and decision making;

      • loss of initiative;

      • memory and emotional disturbances

    • Transcortical motor aphasia may also be present if in left (dominant) hemisphere

NOTE: should watch recording when he was talking about watershed infarcts, b/c information spoken wasn’t on the slide

Describe the Middle Cerebral Artery

• STATs

• Pathways

• Branches of Lat. Hemisphere

• Lat vs Med hemisphere

• Supplies

• Clinical Importance

middle cerebral artery

• STATs:

  • usually (70% of the time) the larger of the terminal branches of the internal carotid

• Pathway/Branches :

  • moves laterally through Sylvian cistern → gives off lenticulostriate arteries to basal ganglia and internal capsule → splits into Sup/Inf. Trunks as it enters Insula → supply inner aspects of the opercula and the lateral surface of the cerebral hemisphere

• Branches of Lateral Hemisphere = variable:

  • Includes branches adj to central sulcus

    • (Precentral, Central and Postcentral (Rolandic) arteries).

• Lat vs Med hemisphere:

  • Lat:

    • MCA supplies central area that is surrounded by Ant/post. cerebral Artery

  • Medial:

    • does NOT supply the medial aspect of the hemisphere.

• Supplies:

  • Primary sensory and motor areas for face and arm

  • Left Side: Broca's/Wernicke's area

  • Optic radiation

  • Parietal association cortex

  • Frontal Eye Field

• CLINICAL IMPORTANCE:

  • Symptoms = depends on which divisions/branch

    • Paralysis of opposite face and arm

    • Sensory deficits over opposite face and arm

    • Aphasia if on left side

    • Visual field defects

    • Inattention and neglect of contralateral side of body or space and denial of illness if on right side

    • Transient paralysis of conjugate gaze to the contralateral side.

Describe the posterior cerebral artery

• Pathway

• Early Branches

• Supplies

• Clinical Presentation

PCA:

• Pathway:

  • Arise from bifurcation of basilar A @ level of interpeduncular cistern → travels laterally over oculomotor nerve → wraps around midbrain in ambient cistern → runs along ventral/medial surface of temporal lobe → continues post. to supply ventral/medial surfaces of the occipital lobe

    • NOTE: includes the calcarine artery. which supplies primary visual cortex.

    • Note: considered part of vertebrobasilar system; but supplies post. area of hemisphere

• Early Branches: Collective supply midbrain, thalamus and choroid plexus.

  • quadriqeminal artery,

  • thalamoperforatinq arteries

  • medial and lateral posterior choroidal arteries

  • thalamoqeniculate artery

• Supplies:

  • Visual cortex

    • Medial surface of occiptal lobe (primary and association cortices)

  • Temporal lobe, caudal parietal lobe, and splenium of corpus callosum

  • Part of thalamus:

    • thalamogeniculate branch — ventral lateral thalamus;

    • thalamoperforating branches to anterior and medial thalamus;

    • posterior choroidal arteries — posterior thalamus, choroid plexus of 3rd and lateral ventricles

• Clinical Presentation:

  • Homonymous Hemianopia (with macular sparing)

    • MCA provides collateral supply to occipital pole- macular vision

  • Pure Alexia (inability to read)

    • w/ involvement of posterior corpus callosum + left visual cortex;

    • color agnosia may also be present.

  • Sensory deficits with deep territory involvement

Describe the segments of the PCA

Describe the vertebral Artery

• Pathway

• Branches supplies

VA:

• Pathway:

  • enter lateral cerebellomedullary cistern after penetrating atlanto-occipital membrane.

• Branches Supplies:

  • part of the medulla oblongata,

  • cerebellum

  • dura of the posterior cranial fossa.

Describe the Posterior Inferior Cerebellar Artery

• Pathway/Supplies

PICA:

• first major branch of the vertebral artery

• Pathway/Supplies:

  • supplies dorsolateral medulla as it wraps around medulla → emerges in cisterna magna where it supplies the choroid plexus of the fourth ventricle and then the posterior and medial parts of the inferior cerebellar surface.

Differentiate between PSA and ASA:

• Origins

• Supplies

posterior spinal artery

• Origins:

  • most often arises from PICA.

  • However, in about 25% of cases, it arises from the vertebral artery.

• Supplies:

  • dorsal part of the spinal cord

  • dorsolateral region of the medulla oblongata

    • caudal to the area served by PICA.

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Anterior Spinal Artery:

• Origin:

  • Prior to joining → basilar artery; each vertebral artery gives rise to an ASA → 2 ASA joins to form one; seen on ventral surface of the spinal cord.

• Supplies:

  • anterior and medial areas of the medulla and spinal cord.

Describe the AICA

• Origins

• Pathway

• Supplies

• Branches

Anterior Inferior Cerebellar Artery

• Origins: First large branch of Basilar artery

  • basilar artery lies on ventral surface of pons in prepontine cistern

• Pathway:

  • wraps around caudal middle cerebellar peduncle → inferior surface of the cerebellum.

• Supplies:

  • ventral and lateral surfaces of cerebellum

  • portion of pons

  • small part of the choroid plexus that extends out of the fourth ventricle.

• Branches:

  • labyrinthine artery

    • arises near CN 7/8 → enters internal acoustic meatus w/ them

    • supply portions of the inner ear

  • paramedian, short and Ionq circumferential branches

    • supply pons

Describe the superior cerebellar artery

• Origins

• Pathway

• Supplies

SCA:

• Origins: basilar artery below it distal bifurcation.

• Pathway:

  • travels caudal to CN III around crus cerebri in ambient cistern → divides into medial + lateral branches.

• Supplies:

  • superior portion of cerebellum

  • most of deep cerebellar nuclei

  • lateral tegmentum of rostral pons.

  • caudal portions of midbrain.

Describe the Circle of Willis

• Perforating groups

• Divisions

• Supplies (ant vs post group)

Circle of Willis

• Perforating Groups:

  • arteries forming circle of Willis give rise to numerous small ( perforating, central, ganglionic) branches that supply the ventromedial structures of the brain.

• Divisions:

  • anteromedial group

  • anterolateral group

  • posteromedial group

  • posterolateral group

• Supplies:

  • Anterior Group

    • optic chiasm

    • anterior hypothalamus

    • anterior perforated substance

    • NOTE: lateral striate (lenticulostriate) arteries are sometimes included.

  • Posterior Group

    • crus cerebri

    • middle + posterior parts of hypothalamus

    • Forms the post. perforated substance as they enter the interpeduncular fossa

    • NOTE: thalamoperforating, tuberothalamic, thalamogeniculate, and medial and lateral posterior choroidal arteries may be included

Differentiate between the med/lat striate artery:

• Origins

• Supply

Medial vs Lateral Striate Arteries:

Origins:

• Medial: Ant. Cerebral Artery (A2)

• Lat: Middle Cerebral Artery (MI)

Supply:

• Medial (recurrent artery of Heubner):

  • rostral part of the head of the caudate & lenticular n

  • anterior limb of the internal capsule.

• Lat (lenticulostriate):

  • head and body of the caudate

  • most of the lenticular n

  • dorsal part of anterior limb

  • genu

  • posterior limb of the internal capsule

Describe the blood supply to the thalamus

• Primarily by?

• Ant. Thalamus

• Post. Thalamus

• Posteriolat.

Blood Supply to Thalamus:

• Primarily by branches of posterior cerebral artery

  • thalamoperforating (Pl area),

  • thalamogeniculate

  • medial and lateral posterior choroidal arteries

    • arise from beyond the branching of the posterior communicating artery (P2 area) on the posterior cerebral artery.

• Ant. Thalamus:

  • Via tuberothalamic (polar) artery

    • branch of posterior communicating artery.

    • WHEN ABSENT (33%):

      • thalamoperforatinq arteries supply this area in addition to the medial thalamus

• Posterior thalamus:

  • posterior choroidal arteries

• Posteriolat:

  • thalamoqeniculate artery

Describe the cerebral venous system

• Lat. Surface:

  • Vessels found

  • Vessel Connections

  • Pathway

• Midsagittal Surface:

  • Pathway

• Base of Brain:

  • Which sinuses are found

• Internal Cerebral Veins

  • What are they?

  • Pathway?

  • Consists of

Lateral Surface of hemisphere:

• Vessels Found:

  • superior anastomotic vein (of Trolard) + inferior anastomotic vein (of Labbe)

• Vessel Connections :

  • w/ superior sagittal + transverse sinuses + superficial middle cerebral vein

• Pathway:

  • vessel courses medially around temporal pole → cavemous sinus.

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Midsagittal Surface:

• Pathway:

  • vessels drain into sagittal sinus.

  • Others from lower medial surface near corpus callosum + medial temporal lobe (the basal vein of Rosenthal) → intemal cerebral veins → qreat cerebral vein (of Galen) → straiqht sinus

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Base of Brain:

• superior + inferior petrosal sinuses link cavernous sinus to transverse sinus and origin of IJV, respectively.

• [REVIEW]: The internal carotid artery passes forward through the lumen of the cavemous sinus along with the abducens nerve (CN VI). The oculomotor n., trochlear n., and the ophthalmic and maxillary branches of the trigeminal n. lie in the lateral wall.

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Internal Cerebral Veins:

• What are they?

  • veins draining the internal structures of the cerebral hemispheres

• Pathway:

  • join @ great cerebral vein and empty into straight sinus.

• Consist of:

  • choroidal veins

    • traveling from choroid plexus

  • thalamostriate (terminal vein) vein

    • runs adj to the caudate nucleus.