Intracranial Arteries Overview

TERMINOLOGY

Abbreviations

• Anterior, middle, posterior cerebral arteries (ACA, MCA,

PCA)

• Anterior, posterior communicating arteries (ACoA, PCoA)

• Basilar artery (BA)

• Vertebral artery (VA)

• Anterior, posterior inferior cerebellar arteries (AICA, PICA)

• Anterior choroidal artery (AChoA)

• Recurrent artery of Heubner (RAH)

GROSS ANATOMY

Anterior Circulation

• ICA and its branches + ACoA, PCoA

Posterior Circulation

• BA and its branches

IMAGING ANATOMY

Overview

• Internal carotid artery

○ Proximal to termination gives off ophthalmic artery,

AChoA, PCoA

○ Terminal bifurcation into ACA (smaller, medial), MCA

(larger, lateral)

○ ACA has 4 segments

– Horizontal or precommunicating (A1) segment

courses medially above optic chiasm, joined by ACoA

to contralateral A1

– Vertical or postcommunicating (A2) segment courses

superiorly in interhemispheric fissure, around corpus

callosum genu

– Distal (A3) segment courses posteriorly under inferior

free margin of falx cerebri, gives off cortical branches

– Perforating arteries arise from A1, ACoA

– RAH arises from distal A1 or proximal A2

○ MCA has 4 segments

– Horizontal (M1) segment courses laterally to sylvian

fissure below anterior perforated substance, bi- or

trifurcates

– "Genu" or "knee" of MCA is gentle posterosuperior

turn toward lateral cerebral (sylvian) fissure

– Insular (M2) segments course within lateral cerebral

fissure, over insula

– Opercular (M3) segments begin at top of insula, turn

laterally in sylvian fissure to reach overhanging

frontal/parietal/temporal opercula

– Cortical (M4) branches emerge from lateral cerebral

fissure, course over hemispheric surface

– Perforating arteries arise from M1

• Basilar artery

○ Courses cephalad in prepontine cistern to terminal

bifurcation ventral to midbrain

– Gives off AICA, superior cerebellar arteries (SCAs),

pontine, midbrain perforating arteries

○ Bifurcates into PCAs, each of which has 4 segments

– Mesencephalic or precommunicating (P1) segment

lies within interpeduncular cistern, curves

posterolaterally from BA to PCoA junction

– Ambient (P2) segment extends from PCA-PCoA

junction, curving around cerebral peduncles just

above tentorium, above oculomotor nerve

– Quadrigeminal (P3) segment extends posteromedially

from level of quadrigeminal plate

– Cortical (P4) branches arise from distal PCA at or just

before reaching calcarine fissure

– Multiple perforating branches arise from BA

bifurcation, proximal P1s

□ Important variant = Artery of Percheron (thalamic,

midbrain perforators all arise from single trunk)

○ Vertebral arteries

– Intracranial (V4) segments enter dura near foramen

magnum

– Give off anterior/posterior spinal arteries, perforating

arteries to medulla, PICA

Vascular Territory

• Vascular distributions of ACA, MCA, PCA vary from

individual to individual, have typical as well as maximum,

minimum territories

• 2 vascular "watershed" zones exist at confluence of

territorial supply, are vulnerable to hypoperfusion

○ Cortical watershed = subpial confluence of cortical

ACA/MCA/PCA branches

○ Deep white matter watershed zone = confluence of

deep cortical penetrating branches, perforating

branches from circle of Willis

• ACA

○ Perforating branches: Corpus callosum rostrum, heads of

caudate nuclei, anterior commissure, anteromedial

putamen/globus pallidus/anterior limb internal capsule

(if RAH present)

○ Cortical branches: Inferomedial frontal lobes, anterior

2/3 of medial hemisphere surface, 1-2 cm over brain

convexity

• MCA

○ Perforating branches: Most of putamen, globus pallidus,

superior half of internal capsule, most of caudate

nucleus, some deep white matter

○ Cortical branches: Most of lateral surface of cerebral

hemispheres, anterior tip (pole) of temporal lobe

• PCA

○ Perforating branches: Much of central brain base

(thalamus, hypothalamus), midbrain, choroid plexus

– Artery of Percheron = thalami, midbrain

○ Cortical branches: Most of inferior surface of temporal

lobe, occipital pole, variable amount of posterolateral

surface of hemisphere

• BA

○ All of PCA territory (including perforating branches),

most of pons, superior cerebellum/vermis

• VA

○ Most of medulla, cerebellar tonsils, inferior

vermis/cerebellar hemispheres

ANATOMY IMAGING ISSUES

Imaging Recommendations

• Late arterial (capillary) phase of DSA with "brain stain"

shows vascular territory

Trauma, and Stroke

Brain: Pathology-Based Diagnoses: Malformations,

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