Blood Supply of the Brain and Spinal Cord Flashcards
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
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
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)
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
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
What do the vertebral arteries form?
Vertebral= ventral aspect of brainstem
-Form basilar arteries
-Right and left posterior cerebral arteries
=posterior circulation
What do the internal carotid arteries form?
Middle and anterior cerebral arteries
Describe the Circle of Willis
Basilar arteries connect with circle of Willis
=Internal carotid= middle and anterior cerebral arteries
Posterior communicating arteries
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
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
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
How can we investigate blood vessels?
MR angiogram
-3D image of vessels
What is infarction?
Morphological entity: a large, localised area of tissue necrosis brought about by reduced blood flow
What is ischaemia?
Perfusion below the metabolic needs of the tissue
What is hypoxia?
Reduced oxygen content in blood
What are the pathologies of stroke?
80% ischaemic
15% intracerebral haemorrhage
5% subarachnoid haemorrhage
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%
What are the vascular injuries to the brain?
- Occlusion of a vessel= infarction
- Hypoperfusion= watershed infarct
- Cardiac arrest= selective vulnerability and global ischaemic injury
What are the types of pathological lesions?
-Focal ischaemic injury =Due to emboli (atheromatous material, air) -Global ischaemic injury =Cardiac arrest =Hypotensive brain injury
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
