(neuro) cerebral vasculature Flashcards
1
Q
what are the perfusion demands of the brain?
A
10-20% of the cardiac output
20% of the body’s oxygen consumption
66% of the liver glucose
= requires a rich blood supply to keep up with the high metabolic demand
2
Q
what percentage of the total body weight is the brain?
A
2%
3
Q
why is the brain very vulnerable if the blood supply is impaired?
A
brain requires a rich blood supply to keep up with the high level of metabolic activity
(i.e. if supply impaired, metabolic activity also slows)
4
Q
how much of the total cardiac output is directed towards the brain?
A
10-20%
5
Q
how much of the total oxygen consumption is directed towards the brain?
A
20%
6
Q
how much of the total liver glucose is directed towards the brain?
A
66%
7
Q
why does the brain have such huge perfusion demands?
A
to keep up with the high metabolic demands
8
Q
how heavy is the brain?
A
1.4 - 1.5kg
9
Q
what are the two components that make up blood supply to the brain?
A
anterior supply and posterior supply
10
Q
describe the anterior blood supply to the brain
A
the brachiocephalic artery gives rise to the common carotid artery
the CCA bifurcates at the level of the laryngeal prominence into the external and internal carotid arteries
the external carotid artery supplies the structures of the face
the internal carotid artery supplies the cranial cavity by travelling up into the cranium via the carotid canal
11
Q
describe the posterior blood supply to the brain
A
the subclavian artery gives rise to the vertebral artery
the vertebral artery goes up posterior through the transverse foramen of the cervical vertebrae
the vertebral artery rise to the skull base and via the foramen magnum, enters the cranial cavity
12
Q
what does the brachiocephalic artery give rise to?
A
common carotid artery
13
Q
into what and when do the common carotid arteries bifurcate?
A
into the R+L internal and external carotid arteries
at the level of the laryngeal prominence (Adam’s apple)
14
Q
what does the external carotid artery supply?
A
supplies structures of the face
15
Q
what does the internal carotid artery supply?
A
structures within the cranial cavity
gives rise to part of the circle of Willis
16
Q
what does the subclavian arteries give rise to?
A
vertebral arteries
17
Q
how does the internal carotid artery enter the cranial cavity?
A
via the carotid canal
18
Q
through which foramen does the vertebral artery travel?
A
transverse foramen of the cervical vertebrae
19
Q
how does the vertebral artery enter the cranial cavity?
A
via the foramen magnum
20
Q
which vertebral segment is the vertebral artery associated with?
A
cervical
21
Q
why is it important that the vertebral arteries are associate with the vertebrae?
A
the bony processes protect the delicate artery
22
Q
where is the circle of Willis found?
A
base of the brain
23
Q
why is it important that the circle of Willis is an anastomotic circuit?
A
if there is a blockage anywhere in the circle, there is a chance of compensatory blood flow from the other side
= so blood supply to brain not completely impaired
24
Q
what is an anastomotic circuit?
A
all the vessels are joined together in one circuit
25
what are the two main feed arteries of the circle of Willis?
internal carotid artery (anterior)
vertebral artery (posterior)
26
describe the structure of the posterior component of the circle of Willis
the two vertebral arteries join to foem the basilar artery
basilar artery gives rise to smaller, pontine arteries laterally
basilar artery also bifurcates into two posterior cerebral arteries
27
what do the posterior vertebral arteries fuse to form?
basilar artery
28
what does the basilar artery give rise to?
two posterior cerebral arteries
29
which cerebral structure is closely linked to the basilar artery?
pons
30
describe the structure of the anteior component of the circle of Willis
the internal carotid artery gives rise to the middle cerebral artery and the anterior cerebral artery
31
what are the two branches of the internal carotid artery?
main branch = middle cerebral artery
second branch = anterior cerebral artery
32
into which fissure does the anterior cerebral artery travel?
longitudinal fissure
33
from where are atherosclerotic plaques common in the circle of Willis?
from the point where the common carotid artery bifurcates
34
give one example of how vessels in the circle of Willis would get blocked
artherosclerotic plaques originate from the point where the common carotid artery bifurcates
commonly travel up the neck into the circle of Willis via the internal carotid artery obstructing blood flow
35
how does the structure of the circle of Willis provide efficient perfusion even when there is a blockage?
anastomotic circuit
in case of a blockage anywhere in the circle, the circuit will allow for compensatory blood flow through the intact, communicating arteries to supply the rest of the brain
36
describe the venous drainage of the brain
cerebral veins drain into to dural venous sinuses which in turn drain into the internal jugular veins that take the venous blood back to the right atrium of the heart
37
how do dural venous sinuses form?
the dura mater is made up of two layers (periosteal and meningeal)
both are closely adherent to each other
the periosteal layer is closely adherent to the cranial bone
if the periosteal and maningeal layer separate from each other, a dural venous sinus forms
38
describe the direction of venous drainage from the superior sagittal sinus
superior sagittal sinus - confluence of sinuses - transverse sinus - sigmoid sinus - internal jugular vein - right atrium
39
what is the falx cerebri?
the dural fold that separates the two cerebral hemispheres
40
what is the falx cerebelli?
the dural fold that separates the two cerebellar hemispheres
41
describe the direction of venous drainage from the great vein of Galen
great vein of Galen - straight sinus - confluence of sinuses - transverse sinus - sigmoid sinus - interior jugular vein - right atrium
42
describe the structure of the meninges
dura mater (periosteal and then meningeal)
arachnoid mater
sub-arachnoid space
pia meter
43
describe the adherence of the dura mater to the skull and each other
periosteal layer is closely adherent to the cranial bone - never separates
meningeal layer is adherent to the periosteal layer but separates to form dural venous sinuses
44
what is extradural/epidural space?
space between the cranial bone (skull) and the periosteal dural mater
(closely adherent to cranium so this space does not naturally occur anywhere along the skull)
45
what are the four types of haemorrhage?
extradural
subdural
subarachnoid
intracerebral
46
what is the main cause of an extradural haemorrhage?
trauma
47
how can an extradural haemorrhage result?
due to a sharp blow to the pterion (the point where four cranial bones - frontal, parietal, sphenoid and temporal - join) and subsequent rupturing of the nearby middle meningeal artery
haemorrhage of the artery causes the periosteal dural to strip away from the skull
48
which bony cranial feature is commonly affected causing an extradural haemorrhage and why?
pterion
(blow to the pterion can cause the middle meningeal artery to rupture and create an extradural space into which it haemorrhages)
49
which artery is most commonly affected in an extradural haemorrhage?
middle meningeal artery
50
why do extradural haemorrhages have an acute onset of symptoms?
usually the result of an arterial bleed where the rupture causes rapid blood loss at high pressure
51
how can one differentiate between extradural and subdural haemorrhages in terms of symptoms?
extradural - rapid, acute onset of symptoms
subdural - delayed, slow onset of symptoms
52
why do subdural haemorrhages have a late onset of symptoms?
usually the result of a venous bleed where the rupture causes slow blood loss at low pressure
53
where do extradural haemorrhages occur?
in a space between the periosteal dural layer and the skull
54
where do subdural haemorrhages occur?
in the region between the dura and arachnoid mater
55
what is the main cause of subdural haemorrhages?
trauma
56
how is an extradural space created?
high-pressure arterial blood haemorrhage causes the periosteal dural to strip away from the skull creating an extradural space
57
what happens to intercranial pressure during a haemorrhage and why?
increases due to the effect of accumulating blood
58
what is a subarachnoid haemorrhage?
bleeding in the region between the arachnoid mater and the pia mater (i.e. subarachnoid space)
59
where does a subarachnoid haemorrhage take place?
in the subarachnoid space
60
what is the main cause of a subarachnoid haemorrhage?
ruptured aneurysms
61
what is an aneurysm?
a bulge/ballooning in the blood vessel caused by a weakness in the vessel wall
62
which individuals are at greatest risk of a subarachnoid aneurysm haemorrhage and why?
hypertensive patients as the increased blood pressure can cause the aneurysm to rupture and a subsequent bleed into the subarachnoid space
63
what is a intracerebral haemorrhage?
a bleed within the brain tissue (i.e. inside the brain)
64
what is the main cause of an intracerebral haemorrhage?
hypertension
65
why is a raised ICP a problem?
only space for the brain in the cranial cavity SO if the ICP increases, compresses structures of the brainstem and can lead to cardiorespiratory centres shutting down
66
what is a stroke?
rapidly developing
focal disturbance of brain function
of presumed vascular origin
of >24 hours duration
67
what are the two types of stroke?
thromboembolic or haemorrhagic
68
how common are thromboembolic strokes?
approx 85% of strokes are thromboembolic
69
how common are haemorrhagic strokes?
approx 15% of strokes are haemorrhagic
70
how quickly do stroke symptoms present?
rapid onset of symptoms
71
what is a transient ischaemic attack (TIA)?
rapidly developing
focal disturbance of brain function
of presumed vascular origin
that resolves completely within 24 hours
72
what is an infarction?
degenerative changes within tissue following (hypoxia caused by) occlusion of an artery
73
what is cerebral ischaemia?
lack of sufficient blood supply to tissue resulting in permanent damage if blood supply is not restored quickly
74
why is a transient ischaemia attack a cause for concern?
it is often a warning for a bigger stroke down the line
75
differentiate between a TIA and a stroke
both are focal disturbances of brain function that are of presumed vascular origin
BUT
stroke = lasts longer than 24 hours whereas TIA = resolves completely within 24 hours
76
differentiate between an infarction and ischaemia
ischaemia is diminished volume of blood perfusion (impaired blood supply)
infarction is the cellular response to that diminished perfusion
77
differentiate between hypoxia/anoxia and ischaemia
while ischaemia is a lack of sufficient blood perfusing tissues, anoxia/hypoxia are a absence/lack of oxygen perfusing tissues
ischaemia - refers to all lack of all blood components
anoxia/hypoxia - lack of oxygen only
78
what is a thromboembolic stroke?
a type of stroke that is caused by a thrombus (blood clot) in the blood vessels supplying the brain
79
define thrombosis
formation of a blood clot (thrombus)
80
define embolism
plugging of a small vessel by material carried from a larger vessel (e.g. thrombi from heart, atherosclerotic debris from the internal carotid artery)
81
give examples of embolisms that can cause occlusion of an artery
thrombi from the heart
atherosclerotic debris from other blood vessels
fat
air (from injections)
82
why is it important to remove all air bubbles before giving an injection?
air can act as an embolism and plug/block a small vessel, occluding the artery, increasing the risk of stroke
83
why is stroke a major public health issue?
third most common cause of death
38,000 deaths per annum in the UK
can cause sever neurological deficit
can cause permanent disability
84
what is the acronym for stroke symptoms?
F - face
A - arms
S - speech
T - time
85
what are the risk factors for stroke?
age, hypertension, cardiac disease, smoking, diabetes mellitus
86
how is cardiac disease a risk factor for stroke?
inefficient cardiac function can increase the risk of thrombi formation
87
how is smoking a risk factor for stroke?
affects vasculature
88
how is diabetes mellitus a risk factor for stroke?
affects vasculature
89
name the three cerebral arteries
anterior cerebral artery
middle cerebral artery
posterior cerebral artery
90
what is the perfusion field of the anterior cerebral artery?
approx 1cm lateral either side of the midline, along the longitudinal fissure all the way back to the parieto-occipital fissure
AND
much of the frontal lobes
91
what is the perfusion field of the middle cerebral artery?
much of the lateral surface of the brain and deep, subcortical brain structures
92
what is the perfusion field of the posterior cerebral artery?
the occipital lobe and the inferior portion of the temporal lobe
93
if the anterior cerebral artery is occluded, what main symptoms does the patient present with?
paralysis of contralateral structures - contralateral hemiplegia (leg > arm, face)
loss of appropriate social behaviours
disturbance of executive functions (e.g. judgement, decision making, intellect) = abulia
94
if the middle cerebral artery is occluded, what main symptoms does the patient present with?
'classic stroke'
contralateral hemisensory deficits
contralateral hemiplegia (arm > leg)
hemianopia
aphasia (if lesion is on left side)
95
if the posterior cerebral artery is occluded, what main symptoms does the patient present with?
visual deficits (i.e. homonymous hemianopia, visual agnosia)
96
why does middle cerebral artery occlusion present with hemianopia?
this visual system runs all the way to the occipital lobe in the back from the frontal lobe and will be affected by a haemorrhage
97
when and why does the middle cerebral artery lesion present with aphasia?
if there is a left sided lesion of the middle cerebral artery, the haemorrhage can affect Broca's area causing expressive aphasia (impairing speech production)
98
define homonymous hemianopia
visual field defect involving either the two right or the two left halves of the visual fields of both eyes
99
differentiate between prosopagnosia and visual agnosia
visual agnosia refers to the inability to name or describe an object when it is placed in front of you
prosopagnosia refers to the inability specifically to recognise human faces
100
how can blood vessels that increase the risk of stroke be identified physically?
yellow discolouration that is indicative of atherosclerotic plaque development, atheroma formation and hardening of the arteries
101
how can blood vessels that increase the risk of stroke be identified physically?
yellow discolouration that is indicative of atherosclerotic plaque development, atheroma formation and hardening of the arteries
