Blood Supply of the Brain and Spinal Cord Flashcards by Freya Millar

What is a stroke?

rapidly developing clinical signs of focal (or global) disturbance of cerebral function, lasting more than 24 hours or leading to death, with no apparent cause other than that of vascular origin

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What is a TIA?

Transient ischemic attacks are brief episodes of neurologic dysfunction caused by focal brain or retinal ischemia, with clinical symptoms typically lasting less than one hour, and without evidence of acute infarction

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Statistics of strokes

Stroke (a vascular disease of the brain) is commonest cause of severe disability
130,000 patients per year have a stroke in UK
15 million strokes worldwide per year (5 million die, 5 million disabled)

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What forms the anterior circulation to the brain?

Carotid= anterior circulation to the brain

Common carotid on left= arch of aorta
Common carotid on right= brachiocephalic trunk
Bifurcation of common carotid to internal and external carotid
Internal through skull into cranial cavity

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What forms the posterior circulation to the brain?

Vertebral arteries

Arise from subclavian arteries
Lying close to cervical vertebrae
Transverse processes of vertebral bodies
Into cranial cavity

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What do the vertebral arteries form?

Vertebral= ventral aspect of brainstem
-Form basilar arteries
-Right and left posterior cerebral arteries
=posterior circulation

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What do the internal carotid arteries form?

Middle and anterior cerebral arteries

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Describe the Circle of Willis

Basilar arteries connect with circle of Willis
=Internal carotid= middle and anterior cerebral arteries
Posterior communicating arteries

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Describe the arterial supply of cerebral hemispheres

Lateral and medial aspects
-Lateral
= middle cerebral artery
=Rim of anterior cerebral supply
=Posterior and inferiorly posterior cerebral artery
-Medial aspect
= Anterior and posterior cerebral arteries

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How do functions of brain areas link with arterial supply?

Lesion to middle cerebral artery= language and motor problems
Lesion to posterior cerebral artery= vision problems

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How do these vessels provide blood to brain tissue?

Main arterial branches
=smaller branches= penetrate cortex= deeper tissues
-Internal carotid= middle cerebral artery= medial, lateral, lenticulo-striate arteries, cortical arteries

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How can we investigate blood vessels?

MR angiogram

-3D image of vessels

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What is infarction?

Morphological entity: a large, localised area of tissue necrosis brought about by reduced blood flow

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What is ischaemia?

Perfusion below the metabolic needs of the tissue

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What is hypoxia?

Reduced oxygen content in blood

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What are the pathologies of stroke?

80% ischaemic
15% intracerebral haemorrhage
5% subarachnoid haemorrhage

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What are the causes of ischaemic stroke?

Atherothromboembolism (large artery stroke)= 50%
Intracerebral small artery disease (lacunar stroke)= 25%
Cardiac source of embolism= 20%
Rare causes= 5%

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What are the vascular injuries to the brain?

Occlusion of a vessel= infarction
Hypoperfusion= watershed infarct
Cardiac arrest= selective vulnerability and global ischaemic injury

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What are the types of pathological lesions?

-Focal ischaemic injury
=Due to emboli (atheromatous material, air)
-Global ischaemic injury
=Cardiac arrest
=Hypotensive brain injury

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What are the causes of thrombo-embolic disease?

-Atherosclerotic plaques
-Arterial dissection
-Emboli
=Atherosclerotic material
=Cardiogenic (AF)
=Fat emboli (trauma)
=Rare cause; neoplasms, air bubbles

Distal branch of MCA blockage vs proximal branch of MCA blockage

-Weakness of one side of face and one arm
vs
Damage to speech area in L hemisphere -> loss of speech (aphasia)

Damage to L visual pathway->
Loss of vision to R
(Hemianopia)

Damage to left motor cortex and internal capsule ->
Weakness of R face, arm and leg

How do we manage strokes?

-Clot buster/ thrombolysis

What are the consequences of lenticulo-striate artery disease?

Small infarct in internal capsule= lacunar Infarction
Infarct in internal capsule, though very small can cause motor weakness in face, arm & leg
No damage to cortical structures or other tracts
no speech or visual loss
cognition intact (vascular dementia= impaired cognitive function)
Small volume of brain damaged: low mortality but can still be very disabling

What is atherosclerosis?

Common lesion of larger arteries; due to accumulation of lipid with associated inflammation
Foamy macrophages

How does an artery become occluded by dissection?

- trauma - Damage to intima - Blood track to medium

Describe fat embolus syndrome

``` Respiratory and neurological Long bone fracture Marrow of femur in blood stream Blockage of small vessels in lungs and brain Multiple haemorrhages Small red globule in vascular system, ```

What happens after haemorrhage?

Liquefactive necrosis Mopped up by macrophages Gliotic scarred brain tissue Loss of cortical structure (grey and white matter)

What are water shed infarcts?

Water shed infarcts are seen when the systemic blood pressure falls to such a level that cerebral blood flow cannot be maintained (hypoperfusion) -Least at overlap of cerebral circulation

What are border zone infarcts?

occur at the boundary between two arterial territories. Usually caused by a drop in blood pressure

Describe global cerebral ischaemia

This develops in the setting of complete cessation of cerebral blood flow, such as may be seen in cardiac arrest. A period of selective vulnerability is then followed by more extensive neuronal loss until all grey matter is affected. The macroscopic changes require resuscitation and a period of several weeks survival. =Laminar necrosis

What are the causes of brain haemorrhage?

``` Hypertension Vascular malformation Neoplasia Trauma Cerebral amyloid angiopathy Iatrogenic (e.g. anticoagulants), other blood dyscrasias ```

What are the small vessel diseases of the white matter?

Mostly associated with aging and hypertension | The terms lipohyalinosis and arteriolosclerosis are the most commonly used terms

What is Lipohyalinosis?

Degenerative process initiated by fibrinoid necrosis. Segmental arteriole disorganisation Ruptures to cause haemorrhage

What is arteriolosclerosis?

Concentric hyaline wall thickening of small arteries and arterioles

What are the common sites for intracerebral haematoma via hypertension?

Basal Ganglia Brainstem Cerebellum

What are the main causes of lobar haematoma?

Cerebral amyloid angiopathy | Abnormal proteins accumulate in blood vessels so predisposed to rupture

What is the main association with subarachnoid haemorrhages?

Vascular malformation Cerebral aneurysms Surrounded by gliotic brain tissue

What are the common sites for cerebral aneurysms?

- Anterior communicating artery - First branching point of the middle cerebral artery - Internal carotid - Branching point of basilar artery

What are cerebral aneurysms?

swelling of artery at a junction. Can rupture and cause subarachnoid (+/- intracerebral) haemorrhage

Where can you see subarachnoid haemorrhage in a MRI?

Sylvian fissure

What are the types of venous infarction?

``` Sagittal sinus thrombosis =Oral contraceptives =Dehydration =Meningitis Cortical vein thrombosis =Meningitis ```

What makes up the posterior circulation?

- Formed by 2 vertebral arteries= basilar - Cerebellar arteries - Pontine arteries

What are the consequences of posterior cerebellar artery infarct?

Infarction of right visual cortex and loss of vision to left | -Involves primary visual cortex in occipital lobe

What causes brainstem infraction?

Occlusion of small branch of basilar artery

Describe blood supply to the spinal cord

- Number of sources - Arise from aorta indirectly - Anterior spinal and 2 small posterior spinal arteries

Describe regulation of cerebral blood flow (CBF)

``` -Within limits, as blood pressure rises, cerebral vessels constrict =resistance increases =maintains flow constant -As pressure falls, vessels dilate =resistance falls =flow constant -60-160 mmHg= autoregulation range ```

How does the regulation of cerebral blood flow change with hypertension?

Cerebral blood flow constant | -Cerebral perfusion pressure increases in chronic hypertension

What are the consequences of persistent high blood pressure?

-Autoregulatory range reset at a higher level -Curve shifts to right -Unwise to rapidly lower high blood pressure to ‘normal’, -When BP falls below 90 mm Hg: =autoregulation fails =CBF drops =ischaemic brain damage can occur