CEREBRAL CIRCULATION
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
ANTERIOR AND POSTERIOR CIRCULATIONSAnterior – Internal carotid arteries
Posterior – Vertebral arteries
INTERNAL CAROTID ARTERY
Course Entry – carotid canal Middle cranial fossa- beside dorsum sellae Enters cavernous sinus Approaches medial side of anterior clinoid
process
Pierces dura and arachnoid maters Moves lateral to optic chiasma Divides into Anterior and Middle cerebral
arteries
BRANCHES OF INTERNAL CAROTID ARTERY[PRIOR TO BIFURCATION]
Occasionally, Anterior choroidal artery supplies
1. Rostral midbrain2. Ventral thalamus3. Subthalamus
ARTERIAL ‘CIRCLE’/’CIRCLE’ OF WILLIS
“CIRCLE” OF WILLIS
Looks more like a polygon Connects anterior and posterior circulations
COMPONENTS
From anterior1. Anterior communicating artery 2. Anterior cerebral artery3. Posterior communicating artery4. Posterior cerebral artery
Alternate route – inadequate, especially in the elderly [atherosclerosis]
Variations1. In approximately 33% persons Posterior
cerebral artery arises from Internal carotid artery
2. One Anterior cerebral artery may be small- anterior communicating artery is wider
TERRITORIES OF CEREBRAL ARTERIES
ANTERIOR CEREBRAL ARTERY
Midline proximity [longitudinal horizontal fissure]
Joined together by anterior communicating artery
Branches 1. Medial striate/recurrent artery of
Heubner→ventral part of head of caudate nucleus, putamen, anterior limb and genu of internal capsule
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
FUNCTIONAL AREAS SUPPLIED
Supplementary and cingulate motor areas Dorsal parts of primary motor and
sensorimotor areas
OTHER ASSOCIATED DEFICITS IN ACA BLOCK
Mental confusion and dysphasia[functional loss in prefrontal cortex, cingulate gyrus, supplementary motor area]
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]
POSTERIOR CEREBRAL ARTERY
BRANCHES
Central branches supply1. Midbrain2. Pineal gland3. Lateral geniculate body4. Lentiform nucleus [partly]5. Thalamus [partly]
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
Posterior choroidal artery supplies 1. Choroid plexus of inferior horn of lateral
ventricle2. Choroid plexus of 3rd ventricle3. Thalamus4. Fornix5. Tectum of midbrain anastomoses with Anterior choroidal
artery
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
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
MIDDLE CEREBRAL ARTERY
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
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 perineumIn most persons, left MCA supplies all cortical areas concerned with language [Wernicke’s,Broca’s]
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
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
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