Transcript Blood Supply of Barin

cerebral circulation & CSF
Blood Supply to Brain
 About 18% -20% of the total blood volume in the body
circulates in the brain(about 750ml), which accounts for
about 2% of the body weight.
 The blood transports oxygen, nutrients, and other
substances necessary for proper functioning of the brain
tissues and carries away metabolites.
 Loss of consciousness occurs in less than 15 seconds
after blood flow to the brain has stopped, and irreparable
damage to the brain tissue occurs within 5 minutes.
 Cerebrovascular disease, or stroke, occurs as a result
of vascular compromise or hemorrhage and is one of the
most frequent sources of neurologic disability.
 Nearly half of the admissions to many busy neurologic
services are because of strokes.
 Cerebrovascular disease is the third most common
cause of death.
Blood Supply to Brain
 The brain is unusual in that it is only able to withstand very short
periods of lack of blood supply (ischaemia). This is because neurons
produce energy (ATP) almost entirely by oxidative metabolism of
substrates including glucose and ketone bodies, with very limited
capacity for anaerobic metabolism. Without oxygen, energy
dependent processes cease leading to irreversible cellular injury if
blood flow is not re-established rapidly (3 to8 minutes under most
circumstances).
 Therefore, adequate cerebral blood flow must be maintained to
ensure a constant delivery of oxygen and substrates and to remove
the waste products of metabolism
 Cerebral blood flow (CBF) is dependent on a number of factors that
can broadly be divided into:
 a. Those affecting cerebral perfusion pressure
 b. Those affecting the radius of cerebral blood vessels
Blood Supply of Brain & Applied
aspects
 internal carotid
circulation
 Vertebrobasilar
circulation
 Circle of Willis
 ‘Stroke’
 Venous drainage
 CSF
Internal carotid artery
 Arises from common carotid artery
 Enters skull through carotid canal of
petrous bone & proceeds through
cavernous sinus curving in an ‘S’ shape
(carotid siphon)
 Supplies rostral 2/3rds of brain including
main parts of basal nuclei & internal
capsule
cerebral circulation
Internal carotid artery
gives off several collateral branches
before it divides into its two terminal
branches:
middle cerebral artery &
anterior cerebral artery
ICA - collateral branches
inferior & superior hypophyseal arteries &
the ophthalmic artery come off the ica as
soon as the artery has entered the skull
posterior communicating & anterior
choroidal arteries are the other named
branches
Ophthalmic artery
 Ophthalmic artery:
 It passes into the orbit through
the optic foramen.
 It supplies the structures of the
orbit, frontal and ethmoidal
sinuses, frontal part of the scalp
and dorsum of the nose.
 Anterior choroidal artery:
 It supplies the optic tract,
choroid plexus of the lateral
ventricle, hippocampus and
some of the deep structures of
the hemisphere, including the
internal capsule and globus
pallidus.
Ophthalmic artery
1. ethmoidal arteries
2. ciliary arteries
3. optic nerve & ophthalmic
artery
4. central retinal artery
5. retinal arteries
6. supratrochlear artery
7. supraorbital artery
8. dorsal nasal artery
9. anterior ciliary artery
Middle cerebral artery
largest terminal branch of the ica
runs between temporal & frontal lobes in
lateral fissure
many perforating branches (7-10 striate
arteries) emerge from the initial segment
of the mca and penetrate the anterior
perforating space to supply:
striatum, putamen, globus pallidus & internal
capsule
middle cerebral striate arteries
middle cerebral artery
MCA divides into several large arteries on
the surface of the insula
continues laterally to emerge on surface of
hemisphere
practically the whole lateral surface of the
brain including motor & sensory areas of
the cortex is supplied by branches of the
mca
cortical distribution of MCA
functional distribution of MCA
anterior cerebral artery
smaller than middle cerebral artery
this terminal branch of the ica runs
between the optic nerve and anterior
perforating space to the region of the
longitudinal fissure
connected with the corresponding artery
on the opposite side by the short anterior
communicating artery
anterior cerebral artery
perforating arteries to the hypothalamus
and to other important structures in the
basal parts of the brain arise from the
proximal part of the ACA
distal to the anterior communicating artery
the two ACA’s ascend in the longitudinal
fissure (where they curve upwards &
backwards above the corpus callosum)
anterior cerebral artery
although the two arteries lie close together
during their course in the longitudinal
fissure they are separated by the falx
cerebri
terminal ramifications of the aca supply
most of the corpus callosum as well as the
medial surfaces of the frontal & parietal
lobes - including leg area in the
paracentral lobule
cortical distribution of ACA
functional distribution of ACA
vertebrobasilar system
two vertebral arteries (carrying about 1/3rd
of cerebral blood) arise from first part of
the subclavian arteries
ascend through foramen transversarium of
cervical vertebrae then enter skull through
foramen magnum
vertebrobasilar system
major branches of vertebral artery
anterior spinal artery
posterior inferior cerebellar artery
bulbar branches
+/- anterior inferior cerebellar artery
both vertebral arteries unite at the
pontomedullary junction to form the basilar
artery
vertebrobasilar system
basilar artery continues in midline of pons
before it bifurcates into its two terminal
posterior cerebral arteries at
pontomesencephalic junction
gives off:
anterior inferior cerebellar artery
internal auditory artery
pontine arteries
superior cerebellar artery
cortical distribution of PCA
functional distribution of PCA
the circle of Willis
anterior & posterior communicating
arteries help form an arterial circle ‘of
Willis’ on the ventral aspect of the brain
provides possibility of collateral circulation
in event of occlusion in one of the major
arteries proximal to the circle
the ‘circle of Willis’
regional blood supply
stroke - definition
“sudden neurological deficit of vascular
aetiology lasting more than 24 hours”
compared with TIA (transient ischaemic attack)
indicates a transient neurological deficit of
vascular origin lasting less than 24 hours
stroke - categorized as
cerebral infarction (80%)
signifying ischaemic brain damage due to
occlusion of a vessel
cerebral haemorrhage
primary pathology involves vascular rupture &
extravasation of blood into surrounding tissue or
compartments
stroke
artery territory
 mca occluson
stroke syndrome
 contralateral hemiplegia,
hemianaesthesia,
homonymous hemianopia,
aphasia, inattention,
cortical sensory loss
 aca occlusion
 hemiparesis
chiefly in the leg
stroke
artery territory
 internal carotid
artery occlusion
 pca occlusion
stroke syndrome
 mixture of aca & mca
syndromes (may be
asymptomatic)
 homonymous hemianopia,
disconnection syndromes,
hemianaesthesia, amnesia,
midbrain & thalamic
syndromes
stroke
artery territory
stroke syndrome
 vertebrobasilar
 quadriparesis, bulbar
thrombosis (basilar
paralysis, impaired gaze,
occlusion)
coma
 ventral pontine
infarction
 quadriparesis, absent
horizontal (but retained
vertical) gaze, normal
conscious state (‘locked in’
syndrome)
stroke
artery territory
 lateral medullary
syndrome
(vertebral, pica or
aica)
stroke syndrome
 ipsilateral ataxia (icp),
Horner’s syndrome,
dysphagia & dysarthria
(CN 9 & 10), vertigo,
nausea & Nystagmus
(vest. nuclei), ipsilateral
facial anaesthesia (CN 5),
contralateral pain &
temperature loss
(spinothalamic tract)
stroke
artery territory
 medial medullary
syndrome
stroke syndrome
 ipsilateral paralysis of
tongue (CN 12),
contralateral
hemiparesis
(corticospinal tract),
contralateral
impairment of touch &
position sense (medial
lemniscus)
lateral medullary syndrome
Weber syndrome
venous drainage
superior sagittal sinus --> right transverse
sinus (confluence of sinuses) --> right
sigmoid sinus
inferior sagittal sinus --> straight sinus -->
left transverse sinus (confluence of
sinuses) --> left sigmoid sinus
the sigmoid sinuses --> (become) internal
jugular veins at jugular foramen
cavernous sinus
located lateral aspect sphenoid
receives blood from pituitary gland, orbit
through ophthalmic veins & middle
cerebral veins
cavernous sinus --> superior & inferior
petrosal sinuses
cavernous sinus
superior petrosal sinus --> junction
transverse & sigmoid sinuses
inferior petrosal sinus --> internal jugular
vein
emissary veins link CS with facial & scalp
veins
cerebrospinal fluid circulation
clear & colorless water-like fluid
formed by choroid plexus
mainly in lateral ventricles (& to lesser degree in
3rd & 4th ventricles)
formation of CSF complex
includes both passive filtration & active
secretary mechanisms
CSF circulation
CSF produced in lateral ventricles
 enters third ventricle through interventricular
foramen
flows through cerebral aqueduct
into fourth ventricle
from fourth ventricle it reaches the
subarachnoid space
CSF circulation
CSF enters subarachnoid space via three
openings:
median aperture (posterior medullary velum)
two lateral apertures (lateral recesses of fourth
ventricle)
CSF circulation
collections of microscopic arachnoid villi
form macroscopic elevations (arachnoid
granulations) that protrude into the lateral
expansions of the superior sagittal sinus
through openings in the dura
flow of CSF is fairly rapid
CSF circulation
total volume of CSF in the ventricular
system & subarachnoid space is only
about 125 ml
but it is estimated that about four times
that amount (~500 ml) is formed during a
24 hr period
a small amount of CSF seeps down
around the spinal cord