The brain receives a large portion of the body's blood supply and oxygen consumption despite being only 2% of body weight. The internal carotid arteries supply the anterior circulation while the vertebral arteries supply the posterior circulation, with these systems connecting at the circle of Willis. Occlusion of cerebral arteries can cause neurological deficits corresponding to the brain areas supplied, such as hemiplegia from middle cerebral artery occlusion or homonymous hemianopia from posterior cerebral artery occlusion. Proper blood flow is crucial for brain function.

1. CEREBRAL CIRCULATION

2. FACTS ABOUT BLOOD SUPPLY
OF BRAIN
 Brain – 2% of body weight
 Receives 17% of cardiac output
 Consumes 20% of entire Oxygen used by the body
 10 seconds of interruption in blood flow leads to
unconsciousness
 Most neurologic disorders are due to vascular
lesions

3. ANTERIOR AND POSTERIOR
CIRCULATIONS
Anterior – Internal carotid arteries
Posterior – Vertebral arteries

5. INTERNAL CAROTID ARTERY
Course
 Entry – carotid canal
 Middle cranial fossa- beside dorsum sellae
 Enters cavernous sinus
 Approaches medial side of anterior clinoid
process

6.  Pierces dura and arachnoid maters
 Moves lateral to optic chiasma
 Divides into Anterior and Middle cerebral
arteries

8. BRANCHES OF INTERNAL CAROTID
ARTERY[PRIOR TO BIFURCATION]

9.  Occasionally, Anterior choroidal artery supplies
2. Rostral midbrain
3. Ventral thalamus
4. Subthalamus

10. ARTERIAL
‘CIRCLE’/’CIRCLE’ OF
WILLIS

11. “CIRCLE” OF WILLIS
 Looks more like a polygon
 Connects anterior and posterior circulations

12. COMPONENTS
 From anterior
2. Anterior communicating artery
3. Anterior cerebral artery
4. Posterior communicating artery
5. Posterior cerebral artery

13.  Alternate route – inadequate, especially in the
elderly [atherosclerosis]
 Variations
3. In approximately 33% persons Posterior cerebral
artery arises from Internal carotid artery
4. One Anterior cerebral artery may be small-
anterior communicating artery is wider

15. TERRITORIES OF
CEREBRAL ARTERIES

18. ANTERIOR CEREBRAL ARTERY
 Midline proximity [longitudinal horizontal
fissure]
 Joined together by anterior communicating
artery
Branches
4. Medial striate/recurrent artery of
Heubner→ventral part of head of caudate
nucleus, putamen, anterior limb and genu of
internal capsule

20. AREA SUPPLIED
 Medial part of orbital surface of frontal lobe
[includes olfactory bulb and tract]
 Medial surfaces of frontal and parietal lobes
 Corpus callosum
 A strip on lateral surface

21. FUNCTIONAL AREAS SUPPLIED
 Supplementary and cingulate motor areas
 Dorsal parts of primary motor and sensorimotor
areas

22. OTHER ASSOCIATED DEFICITS IN
ACA BLOCK
 Mental confusion and dysphasia[functional loss
in prefrontal cortex, cingulate gyrus,
supplementary motor area]

23. EFFECTS OF OCCLUSION
 Paralysis and sensory deficits in contralateral
leg, perineum
 Urinary incontinence [inadequate perineal
sensation, defective cortical control of pelvic floor
muscles]
If obstruction is proximal to anterior
communicating artery [blocked medial striate
artery]
 UMN weakness of face, tongue and upper limb
[lesion in or near genu]
 Ipsilateral anosmia [maybe]

24. POSTERIOR CEREBRAL
ARTERY

26. BRANCHES
 Central branches supply
2. Midbrain
3. Pineal gland
4. Lateral geniculate body
5. Lentiform nucleus [partly]
6. Thalamus [partly]

27.  Temporal branches→ inferolateral and medial
surfaces of temporal lobe, much of
parahippocampal gyrus
 Calcarine and parieto-occipital branches→
peripheral strip on lateral surface
 Calcarine branch supplies all of primary
visual cortex and some of Visual association
cortex

28.  Posterior choroidal artery supplies
d Choroid plexus of inferior horn of lateral
ventricle
f Choroid plexus of 3rd ventricle
f Thalamus
f Fornix
f Tectum of midbrain
anastomoses with Anterior choroidal artery

29. EFFECTS OF OCCLUSION
 Blindness in contralateral visual fields of both
eyes – homonymous hemianopia
 Disturbance of memory – transient
 In case of dominant hemisphere being affected,
the infarct extends into corpus callosum→
disconnection of contralateral visual area from
language area of dominant hemisphere→ alexia
in addition to homonymous hemianopia

30. SPECIAL CIRCUMSTANCES
 Expanding space-occupying lesion in
supratentorial compartment→ herniation of
uncus and midbrain→ compression of one or both
PCA→ necrosis of areas supplied [even after
surgical correction of cause]→ cortical
blindness+inability to form new memories
 Traumatic Intracranial hemorrhage can lead to
the same consequences

31. MIDDLE CEREBRAL
ARTERY

32.  Larger, more direct continuation of ICA
 Occupies lateral sulcus
 Central branches →Head of caudate
nucleus,Putamen, Lateral pallidum, Internal
capsule [anterior limb, genu, posterior limb],
External capsule, Claustrum, Lateral
hypothalamus

33. FUNCTIONAL AREAS SUPPLIED
 Most of primary motor and premotor areas
 Frontal eye field
 Primary somatosensory area
 Geniculocalcarine tract
EXCEPT motor and sensory cortex for
lower limb and perineum
In most persons, left MCA supplies all
cortical areas concerned with language
[Wernicke’s,Broca’s]

34. EFFECTS OF OCCLUSION
 Contralateral paralysis of lower face, upper limb
 General somatosensory deficits in the same areas
 Astereognosis
 Hemianopia in contralateral visual fields of both
eyes
 Global aphasia if dominant hemisphere involved
 Aprosodia if non-dominant hemisphere involved

35.  Cortical neglect, if right hemisphere involved
 Conjugate eye movements affected[ at rest, eyes
turn towards the side of lesion]
 Hearing unaffected [bilateral representation]
 Obstruction to central branches- contralateral
hemiplegia without aphasia