Blood supply to the CNS

Question 1

Summarise the metabolic demands of the brain

Answer 1

Brain makes up 2% of body weight but uses:
10-20% of cardiac output
20% of body O2 consumption
66% of liver glucose

The brain is therefore very vulnerable if its blood supply is impaired

Question 2

What can left carotid artery stenosis lead to

Answer 2

Stroke

Question 3

Summarise the two sources of blood supply to the brain

Answer 3

Vertebral arteries (posteriorly)
Internal carotid arteries (anteriorly)

Question 4

Where does the common carotid artery split

Answer 4

At the level of the laryngeal prominence (Adam’s apple)
Splits into external and internal carotid arteries
External supplies the vessels of the face and the surface soft tissue
The internal carotid- unbranched- emerges through the base of the skull- to supply the anterior part of the circulation. in the anterior cranial cavity.

Question 5

What is the key difference between the external and internal carotid arteries

Answer 5

External- unbranched

Internal- branched

Question 6

Describe the passage of the vertebral arteries into the skull

Answer 6

First branch of the subclavian artery

The vertebral arteries pass through the transverse foramina of the cervical vertebrae and through the foramen magnum into the brain to join the rest of the circulation

Question 7

Summarise the carotid arteries

Answer 7

Carotid arteries: Left common carotid formed from aortic arch and right common carotid from the right subclavian; branch at the carotid sinus to form the internal and external carotids - the internal carotids then ascend to supply the brain

Question 8

How does the internal carotid artery enter the skull

Answer 8

Through the carotid canal

Question 9

What is the circle of willis

Answer 9

Anastamoses of the ICA and vertebral arteries- gives off the cerebellar arteries
The loop formed between the basilar artery and the internal carotid vessels (via the anterior and posterior communicating arteries) is known as the circle of Willis.

Question 10

What is important to remember about the vertebral arteries

Answer 10

Often asymmetric in size

Question 11

Describe the two branches of the internal carotid arteries

Answer 11

The internal carotid arteries send off two branches (the anterior and posterior communicating arteries) before becoming the middle cerebral artery. This artery has an extensive territory, supplying most of the surface of the brain and some of the basal ganglia.

Question 12

Describe the anterior cerebral arteries

Answer 12

The anterior cerebral arteries travel forward on either side of the longitudinal fissure to supply the medial surface of each cerebral hemisphere.

Question 13

Describe the basilar artery

Answer 13

•
The vertebral arteries join at the inferior border of the pons to form the single basilar artery. Branches of the vertebral arteries and the basilar artery supply the medulla, pons and cerebellum.

Question 14

Describe the posterior cerebral arteries

Answer 14

The posterior cerebral arteries supply the occipital and temporal lobes. Most of their input is derived from the basilar artery, with a contribution from the carotid vessels via the posterior communicating arteries.

Question 15

Describe carotid endarterectomy

Answer 15

Some people can have their common carotid artery completely occluded by stenosis- but blood flow will be compensated by the other carotid artery (circle of willis)
However, we still need to treat the occlusion- pipe clean the carotid arteries

Question 16

Which of the following arteries of the circle of Willis is unpaired?

Answer 16

Anterior communicating artery

Question 17

Where does the cerebral veins drain

Answer 17

Into the sinuses- the cranial cavity is not about large cerebral veins.

Question 18

Ultimately, where do the venous sinuses drain

Answer 18

Into the back of the head- which then then drains into the internal jugular veins- in side of neck next to carotid arteries

Question 19

Summarise the venous drainage of the brain

Answer 19

Cerebral veins
Venous sinuses
Dura mater
Internal jugular vein

Question 20

State the names of the sinuses that are at the top and bottom of the falx cerebri

Answer 20

Superior and inferior saggital sinuses

Question 21

What is the name given to the place where all the sinuses meet

Answer 21

The confluence of sinuses

Question 22

What connects the inferior sagittal sinus to the confluence of sinuses

Answer 22

The straight sinus

Question 23

Which sinus ascends to join the confluence of sinuses

Answer 23

the occipital sinus

Question 24

Which two sinuses run along the temporal bone

Answer 24

The superior and inferior petrosal sinuses

Question 25

12. Which main sinus drains into the internal jugular vein through the jugular foramen?

Answer 25

Sigmoid sinus

Question 26

13. Which sinus connects the confluence of sinuses to the sigmoid and superior petrosal sinuses?

Answer 26

transverse sinus

Question 27

14. Which sinus runs along the sphenoid and parietal bones?

Answer 27

Sphenoparietal sinus

Question 28

15. Which sinuses run on either side of the pituitary stalk?

Answer 28

Anterior and posterior inter cavernous sinus

Question 29

Summarise venous drainage of the brain

Answer 29

Venous drainage of the brain begins internally as networks of small venous channels lead to larger cerebral veins, cerebellar veins, and veins draining the brainstem, which eventually empty into dural venous sinuses. The dural venous sinuses are endothelial-lined spaces between the outer periosteal and the inner meningeal layers of the dura mater, and eventually lead to the internal jugular veins.

Question 30

What else drains into the dural sinuses

Answer 30

Also emptying into the dural venous sinuses are diploic veins, which run between the internal and external tables of compact bone in the roof of the cranial cavity, and emissary veins, which pass from outside the cranial cavity to the dural venous sinuses
The emissary veins are important clinically because they can be a conduit through which infections can enter the cranial cavity because they have no valves.

Question 31

Summarise the small branches of the basilar artery

Answer 31

The basilar artery travels in a rostral direction along the anterior aspect of the pons (Fig. 8.39). Its branches in a caudal to rostral direction include the anterior inferior cerebellar arteries, several small pontine arteries, and the superior cerebellar arteries. The basilar artery ends as a bifurcation, giving rise to two posterior cerebral arteries.

Question 32

What are the branches of the internal carotid artery

Answer 32

Entering the cranial cavity each internal carotid artery gives off the ophthalmic artery, the posterior communicating artery, the middle cerebral artery, and the anterior cerebral artery

Question 33

Describe the anastomotic interconnection of the cerebral arteries

Answer 33

The cerebral arterial circle (of Willis) is formed at the base of the brain by the interconnecting vertebrobasilar and internal carotid systems of vessels (Fig. 8.38). This anastomotic interconnection is accomplished by:
▪
an anterior communicating artery connecting the left and right anterior cerebral arteries to each other, and
▪
two posterior communicating arteries, one on each side, connecting the internal carotid artery with the posterior cerebral artery

Question 34

Which vein drains the dural venous sinuses

Answer 34

The internal jugular vein

Question 35

Define stroke

Answer 35

Cerebrovascular accident (CVA)
Definition:
rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration
Results in impaired neurological function

Question 36

What re the two types of stroke

Answer 36

Infarction (85%) or haemorrhage (15%)

Blockage or bleed- haemorrhage- likely trauma related

Question 37

Define transient ischaemic attack (mini-stroke)

Answer 37

rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours

Question 38

What are the two causes of ischaemic stroke (infarction)

Answer 38

Ischemic strokes are further divided into those caused by thrombotic or embolic phenomena. The latter is by far the commonest type of stroke and is often caused by emboli that originate from atherosclerotic plaques in the carotid arteries that migrate into and block smaller intracranial vessels.

Question 39

Describe some rare causes of ischaemic strokes

Answer 39

Thromboembolic infarcts are predominantly secondary to atheroma or cardiogenic emboli, although very rarely infarcts may be seen secondary to embolic material such as fat (fractured long bones) or malignancy.

Question 40

What is meant by infarction

Answer 40

Degenerative changes which occur in tissue following occlusion of an artery
Essentially, dead tissue that has lost its blood supply- no oxygen or nutrients

Question 41

Define cerebral ischaemia

Answer 41

Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly

hypoxia/anoxia- this is the oxygen component
But not just about oxygenation- reduced supply of nutrients and glucose too- global insufficient blood supply

Question 42

describe the significance of TIAs

Answer 42

They are warnings
Elderly patients may come in with a. bit of a turn- dizziness, confusion
may be indicative of a big risk of stroke
temporary blockage to vessel- clot (most likely) or bit of atherosclerotic broken off- but quickly resolved and cleared- so no neurological deficit- but big risk of full-blown stroke- needs to be carefully managed.

Question 43

Define thrombus

Answer 43

formation of a blood clot (thrombus)
If blood is static in the heart- it can begin to form thrombi- and if turbulent flow- can be thrown to the head- thrombosis

Question 44

Define embolism

Answer 44

plugging of small vessel by material carried from larger vessel e.g. thrombi from the heart or atherosclerotic debris from the internal carotid
can break away to vessels in the brain and cause stroke
can get fat and air emboli

Question 45

How will atherosclerosis show on the post-mortem

Answer 45

Yellow colour in the vessel wall- atheroma- fatty build up at vessel wall (most likely to occur at bifurcations)- completely occluded vessel

Question 46

What should you look for on a post-mortem or imaging when looking for signs of pathology

Answer 46

Look for any asymmetries
Changes in colour- lose differentiation of colour from white to grey mater- sign of infarction or dead tissue
If it takes out a lot of the lateral part of the brain (on a coronal section)- likely to be middle cerebral artery

Question 47

Summarise haemorrhagic strokes

Answer 47

Haemorrhagic infarcts are mostly seen in the setting of hypertension, although other causes include underlying malignancy or vascular malformation, trauma, vasculitis, recreational drugs and iatrogenic causes.
Hypertensive infarcts occur most frequently in the following sites:
•
The putamen and the internal capsule
•
Central white matter
•
Thalamus
•
Cerebellar hemisphere
•
Pons.

Question 48

Describe the nature of TIAs and what patients present with

Answer 48

They are thromboembolic in nature and should be recognized and managed promptly because they are an indication that a full stroke may be imminent. Carotid territory transient ischaemic attacks present with:
•
Transient monocular blindness (amaurosis fugax)
•
Transient sensory or motor symptoms of the face, arm or leg
•
Transient aphasia.

Patients often describe amaurosis fugax as ‘a black curtain descending over one eye’.

Question 49

Summarise vertebrobasilar TIAs

Answer 49

Vertebrobasilar transient ischaemic attacks present with a combination of:
•
Dysarthria
•
Vertigo and unsteadiness
•
Diplopia
•
Circumoral paraesthesiae
•
Sensory or motor symptoms affecting the limbs singly or in combination
•
Cranial nerve palsies.

Question 50

Summarise the epidemiology of strokes

Answer 50

3rd commonest cause of death
100,000 deaths in UK per annum
50% of survivors are permanently disabled
70% show an obvious neurological deficit

Question 51

List the risk factors for stroke

Answer 51

Largely lifestyle:
Age
Hypertension- particularly for haemorrhagic stroke- especially if you have aneurysms or inherent weakness in vessel wall- can burst
Cardiac disease- static blood in valves of heart- may start throwing of thrombi
Smoking
Diabetes mellitus- microvascular complications

Question 52

Describe the perfusion field of the anterior cerebral artery

Answer 52

medial, anterior and superior regions of the cerebrum - supplies the lower limb and frontal lobe (decision making and social interaction)
e anterior cerebral artery actually supplies quite far back to the parieto-occipital fissure.

Question 53

Describe the perfusion field of the middle cerebral artery

Answer 53

lateral and anteroinferior regions of the cerebrum - supplies deep structures as cortex fibres will transverse these region
The middle cerebral artery extends laterally and emerges through the lateral fissure between the frontal and temporal lobes – it supplies the front 2/3 of the lateral part of the hemisphere
 The middle cerebral artery also supplies some of the sub-cortical grey matter towards the centre of the brain.

Question 54

Describe the perfusion field of the posterior cerebral artery

Answer 54

posteroinferior regions of the cerebrum - largely occipital lobe with inferior temporal lobe
The posterior cerebral artery supplies the medial and lateral parts of the posterior part of the hemisphere

Question 55

Summarise CNS tissue vascularisation

Answer 55

CNS Tissue Vascularisation: arteries enter tissue as branches of surface pial vessels, which then branch to penetrate into the parenchyma - forming capillaries that drain into venules

Question 56

Relate the importance of the motor and sensory homunculus to the blood supply

Answer 56

Arranges as an upside-down man
Therefore, middle cerebral will supply the torso, head and abdomen
Whereas the anterior cerebral will supply the lower limbs
Essentially, the leg is more medial to the arm
This relates to the differences in clinical presentations seen between anterior and middle cerebral strokes

Question 57

Summarise the presentation of a stroke where the anterior cerebral artery is affected

Answer 57

Paralysis (hemiparesis) of contralateral leg > arm, face
Disturbance of intellect, executive function and judgement (abulia)
Loss of appropriate social behaviour- hyper sexual, over-aggressive- due to frontal lobe deficit

Question 58

Summarise the presentation of a stroke where the middle cerebral artery is affected

Answer 58

This is a CLASSIC STROKE
Contralateral hemiplegia in the ARM more than the leg
Contralateral hemisensory deficits- sensory cortex in post-central gyrus
Hemianopia- blindness over half the field of vision- exposes a design flaw in the brain- eyes at front- processing at back- vision integral thoughout brain
Aphasia (can’t speak) – left-sided lesion of the middle cerebral artery will result in aphasia because the language centres are more on the left side than the right
More likely to be complete paralysis (hemiplegia) as although superficially the motor cortex may be spared- the sub-cortical motor fibres going down to the body may be affected

Question 59

What is meant by an expressive aphasia

Answer 59

Can understand by can’t formulate words

Broca’s > Wernicke’s

Question 60

Summarise the presentation of a stroke where the posterior cerebral artery is affected

Answer 60

The posterior cerebral artery supplies the occipital lobe, which is where the primary visual cortex is located
This causes visual defects such as homonymous hemianopia and visual agnosia (unable to recognise what you are seeing)
prosopagnosia- the inability to recognise the face of someone you have known

Highlights the role of occipital lobe in not only processing the image but understanding and interpreting it too

Question 61

Summarise lacune infarcts

Answer 61

Lacune is a small cavity in the brain- seen on post-mortem
Appear in deep structures as a result of small vessel occlusio body has compensatory mechanisms- will clear clot and dead tissue- leaving cavity- thus the association with hypertension
Deficit is dependent on anatomical location- most likely to occur in basal ganglia
Hypertension
Often no clinical presentations

Question 62

Summarise the four types of haemorrhagic stroke

Answer 62

Extradural - trauma, immediate effects
Subdural - trauma, delayed effects
Subarachnoid - ruptured aneurysms
Intracerebral – spontaneous hyper-tensive

Question 63

Describe an extradural haemorrhage

Answer 63

Trauma of middle cerebral artery- weak point in side of head (temple)- where four bones meet
Bleed raises ICP- which pushes the dura mater away from the inside of the skull- can shut down on brainstem as it is pushed down by the raised ICP
Neurosurgical emergency- drill a flap into the bone- remove the bleed- re-build the vessel- need to get. rid of bleed quickly or the patient will die
no space-blood creates the space- why ICP raises

Question 64

Describe a subdural haemorrhage

Answer 64

Bridging veins between dura and arachnoid space
Trauma- ruptures these veins- low pressure-so delayed effects- difficult to pick up- subdural space where blood can accumulate without any noticeable effects initially
History of loss of consciousness- hit head- back to normal- die 24 hours later
In U,K- if patient presents with history of head injury and loss of consciousness- kept in overnight for observation

Question 65

Describe subarachnoid haemorrhages

Answer 65

All vessels at base of brain are in subarachnoid space- if burst- subarachnoid bleed
Most likely due to inherent weaknesses in the vessel walls (Berry’s aneurysms) most people live without knowing them- often picked up accidentally on a scan
Choice to intervene dependent of clinician
If intervening- go through vessels in the groin- to insert a platinum coil to prevent rupturing

Question 66

Describe intracerebral haemorrghages

Answer 66

Bleed within brain tissue itself
Goes back to hypertension
usually due to spontaneous hypertensive rupture of small vessels

Question 67

Summarise sub-arachnoid haemorrhages

Answer 67

Subarachnoid haemorrhage is relatively uncommon and typically occurs in people between the ages of 35 and 65 years. Rupture of a cerebral berry aneurysm is the commonest cause (70%), with arteriovenous malformations accounting for 15% of cases. Berry aneurysms result from a defect in the media and elastica of the cerebral arteries, causing the media to bulge outward covered only by the adventitia. Genetic factors are important, particularly polycystic kidney disease and coarctation of the aorta.

Question 68

describe the presentation of a sub-arachnoid haemorrhage

Answer 68

The severity of symptoms is related to the severity of the bleed with:
•
Severe headache ‘as if hit on the head with a sledge-hammer’
•
Nausea and vomiting.

The signs of subarachnoid haemorrhage are:
•
Neck stiffness, positive Kernig’s sign (pain on passively extending the knee when the hip is flexed to 90º) – both are signs of meningeal irritation, which develop 6 hours after the bleed
•
Focal neurological signs (particularly III nerve palsy in posterior communicating artery aneurysms)
•
Drowsiness, depressed consciousness
•
Retinal haemorrhages.

Question 69

What is common with a sub-arachnoid haemorrhage

Answer 69

This may show frank blood or xanthochromia (indicative of previous blood in the cerebrospinal fluid).
Vessels in contact with CSF

Question 70

What is meant by a blown lobe

Answer 70

The whole lobe is covered with blood in the sub-dural space- subdural haemorrhage

Question 71

Describe the appearance of a sub-arachnoid bleed on the post-mortem

Answer 71

Everything is obscured by blood in the sub-arachnoid space

Difficult to treat as you need to get into the vessels

Question 72

Describe brainstem (vertebrobasillar strokes)

Answer 72

cranial nerve palsies, ataxia, spinal tract symptoms, depressed consciousness 
Difficulty breathing.
Difficulty speaking.
Problems with chewing and swallowing.
Partial or complete hearing loss.
Blurred vision.
Weakness of the limbs.
Paralysis.
Numbness or loss of sensation.

Question 73

How can the full extent of neurological injury be evaluated

Answer 73

The full extent of neurological injury can be evaluated on subsequent magnetic resonance imaging (MRI) of the brain, which has better soft tissue resolution compared to CT. MRI is also useful for identifying strokes that may be too small to detect on a CT scan. MRI scans are produced by using complicated algorithms that create a series of images, also known as sequences. Various sequences can be obtained to assess different anatomical and physiological properties of the brain. A stroke, whether acute or chronic, will appear as a bright region on a sequence that is sensitive to fluid (T2 weighted)

Question 74

Describe the additional diagnostic workup of stroke

Answer 74

Additional diagnostic workup of stroke includes hematological and biochemical blood tests to identify causes such as hypoglycemia or underlying clotting disorders. A toxicology screen may be useful to identify substance intoxication, which can mimic stroke.

Question 75

What are the most likely causes of stroke in younger patients

Answer 75

In younger patients underlying clotting disorders, use of oral contraceptives, and illicit substance abuse (such as cocaine) are additional causes.

Question 76

What should be done if a stroke is suspected

Answer 76

Following initial clinical history taking and neurological examination, all patients with suspected stroke should undergo urgent brain imaging with computed tomography (CT). This is to identify hemorrhagic strokes for which thrombolytic therapy is contraindicated and to exclude an alternative diagnosis such as malignancy. In ischemic stroke, early CT imaging may appear normal or can show a relatively darker area of low density that corresponds to the region of abnormal brain perfusion. Due to subsequent brain edema and swelling, the affected brain also loses its normal sulcal pattern (Fig. 8.40A). If thrombolysis is performed, a 24-hour follow-up CT scan is routinely carried out to evaluate for complications such as intracranial hemorrhage.

Question 77

What is meant by the patient becoming ‘coned’

Answer 77

 When a patient is “coned”, their brainstem falls through the foramen magnum and the become braindead.