This document summarizes the anatomy of the circle of Willis and cerebral blood supply. It describes the circle of Willis as a polygonal anastomotic channel at the base of the brain supplied by the internal carotid and vertebral arteries. It then discusses the branches and functions of the circle of Willis, cortical and central arteries, lenticulostriate arteries, and the blood-brain barrier. Finally, it provides details on the regional arterial supply of different brain regions and applied anatomy related to various neurological syndromes.

1. Maj Rishi Pokhrel
Dept of Anatomy
NAIHS

2. Circle of Willis
(Circulus Arteriosus)
• Polygonal anastomotic channel
•Base of brain (interpeduncular fossa)
•2 sets of arteries
– Int Carotid - Frontal & parietal lobes
and parts of temporal & occipital
lobes
– Vertebrobasilar - brainstem,
cerebellum, parts of temporal
&occipital lobes

3. CIRCLE OF WILLIS (Circulus Arteriosus)
•Functions
–Equalizes blood flow to different parts of brain
–If 1 arterial system occluded, bld. passes via
communicating As to prevent infarction

5. Branches:
•Anteromedial: from ant cerebral & ant
communicating As
•Paired Anterolateral: from ant & mid cerebral As
•Paired Posterolateral: from post cerebral A
•Posteromedial: from post cerebral & post comm. A

7. Cortical & Central Arteries
Cortical Arteries
• Arise from ant, mid & post Cerebral As
• Ramify on pia, form anastomoses
• Supply grey matter & subjacent white matter
• Are in 2 sets
• Short cortical-extend upto middle of grey matter
• Long cortical – 3-4cm long, run upto superficial white matter
- NOT actual end-arteries

8. Central Arteries
• Branches of Circle of Willis
• Penetrate base of brain
• Supply int capsule, thalamus & basal ganglia
• Arranged in 4 sets
– Antero med
– paired anterolat
– Paired posterolat
– Postero med
• Both central & cortical As are surr. by pial sheath
upto pre-capillary level

9. Lenticulostriate Arteries
• Clinically - most important
• Central branches of MCA
• Pierce ant perforated substance & enter white matter
• Pass through lentiform nucleus to reach int. capsule
• Supply upper part of int capsule, lentiform & caudate
nuclei
• Some are long, slender, thin-walled & prone to rupture in
hypertension-called Charcot’s arteries of cerebral
hemorrhage.

11. BLOOD BRAIN BARRIER
Exists at capillary level, from inside to outside
consists of:
• endothelial cells of capillaries with tight
junctions
• Basement membrane of endothelial cells
• Perivascular extensions of astrocytes
• Intercellular space filled with tissue fluid
• Neuronal cell membrane

13. Cerebral cortex – segmental supply

16. Regional arterial supply of Brain
•Brain stem:
– Medulla oblongata: branches of vertebral, ant & post spinal, PICA and basilar A
which enter along ant med fissure and post med sulcus. Vs supplying central
substance enter along with rootlets of CN IX, X, XI and XII. Additional supply is
from pial plexus of same A.
– Pons: basilar A, AICA and PICA. Direct br from basilar A enter along ventral
median groove, others enter along CN V, VI, VII, VII and from pial plexus.
– Midbrain: PCA, SCA and basilar A, crura by Vs entering their med and lat sides.
Med Vs also supply sup-med part of tegmentum including CN III nucleus ; lat Vs -
lat part of crus and tegmentum. Colliculi by 3 Vs on each side from PCA and SCA.
Additional supply to crura, colliculi and their peduncles comes from post-lat group
of central br of PCA.
•Cerebellum: by PICA, AICA and SCA, which from superficial plexus on cortical surface,
anastomosis b/w deeper sub-cortical branches has been postulated. Choroid plexus of 4th
ventricle is supplied by PICA.
•Optic chiasma, tract and readiation: Chiasma – by ACA but median zone depends on
rami from ICA reaching it via pituitary stalk. Tract; ant choroidal and post comm A.
Radiation: deep br of MCA and PCA.

17. • Diencephalon:
– Thalamus: br from post comm A, PCA and basilar A; contribution from ant chorodial
A is doubtful.
– Median br from post choroidal A: supplies post commissure, habenular region, pineal
gland and medial parts of thalamus including pulvinar.
– Hypothalamus: Small central br from circle of willis and its br.
– Pituitary gland: hypophyseal br of ICA
– Lamina terminalis: ACA and ant comm A
– Choroid plexus of 3rd
and lat ventricles: br from ICA and PCA.
• Basal ganglia: majority from striate A from roots of ACA & MCA which enter brain from ant
perforated substance and also supply internal capsule.
– Caudate Nu: additional supply from ant and post choroidal A
– Post-inf part of lentiform complex: thalamo-striate br of PCA.
– Ant choroidal A, preterminal br of ICA supply both segments of globus pallidus and caudate Nu,
ligation of this VS (known by serendipity) alleciates the symptoms of parkinson’s disease by
infarction of globus pallidus (lead to initiation of pallidotomy).
• Internal Capsule: by central br of circle of willis and its br, mainly med and lat striate A which come
from either ACA or ACA and also supply basal ganglia.
– Lateral striate A: ant limb, genu and most of post limb. Commonly involved in ischemic and
hemorrhagic stroke.
– Charcot’s A of cerebral hemorrhage : larger striate br of MCA.
– Medial strate A: br of proximal part of MCA or ACA supplies ant limb, genu and basal ganglia.
– Ant choroidal A from ICA: contributes to ventral part of post limb and retrolentiform part of int
capsule.

18. Applied anatomy

19. Lateral medullary
syndrome
Medial medullary
syndrome

20. Lateral medullary syndrome of Wallenberg
• Occlusion of PICA
• Posterolateral part of medulla is damaged
• Involvement of
– spinal nuc & tract of V nerve – ipsilateral loss of pain
& temp from face & forehead
– spinal lemniscus (lat spinothalamic tract) –
contralateral loss of pain & temp from body below face
– Nucleus ambiguus – paralysis of muscles of soft
palate, pharynx & larynx- dysarthria & dysphagia
– Vestibular nuclei- giddiness
• Crossed hemianesthesia

21. Medial Medullary Syndrome
• occlusion of ant spinal artery which supplies
medial part of medulla
• Involvement of
• CN XII nucleus – ipsilateral LMN paralysis of
tongue ; deviated to affected side
• Pyramidal fibres - contralateral UMN paralysis
• Medial lemniscus (post column fibres) –
contralateral loss of fine touch & discrimination
• Crossed motor paralysis

22. Pontine Hemorrhage
• Pontine arteries rupture
• Hyperpyrexia – thermoregulatory mechanism disrupted
• Pinpoint pupils – contraction of sphincter pupillae
• Coma – reticular formation lesion
• Contralateral UMN paralysis – pyramidal fibres involved

23. Pons
•Raymond’s syndrome: Alternating abducent hemiplegia
(lesion in medial cranial part of pons)
•Milalard Gubler syndrome: Alternating facial hemiplegia
(lesion in medial caudal part of pons)
•Lesions in lateral part of mid pons: alternating trigeminal
hemiplegia
Midbrain
•Weber’s syndrome: crossed III CN hemiplegia
•Benedikt’s syndrome: https://en.wikipedia.org/wiki/Benedikt_syndrome
•Parinaud’s syndrome: https://en.wikipedia.org/wiki/Parinaud%27s_syndrome

24. Veins on Superolateral surface of cerebrum

26. ?