Blood Supply to the Brain Flashcards
How much of the cardiac output does the brain receive (%)?
15%
Average brain blood flow = 46mL/100 grams of brain per minute
How much of the total body oxygen and body glucose does the brain use (%)?
20% and 25% respectively
How long of anoxia until a person is unconscious? How long for permanent unconsciousness?
20 seconds
More than 5 minutes
What is special about the arteries in/around the brain?
They have very thin walls compared to arteries in other areas of the body, so they are easily blocked/distorted/ruptured.
What is special about the veins in/around the brain?
They have no valves, and also no muscles or elasticity to help venous return (they rely on gravity).
How much of the total cerebral blood flow is from the internal carotid arteries?
Where is the rest from?
80%
Vertebral arteries
Can the anterior and posterior communicating arteries normally be seen on an angiogram?
No, because under normal situations they are closed. They only open if the pressure in one of the hemisphere drops (i.e. when the pressure is no longer equal on both sides).
How many % of the population have the classic Circle of Willis?
34.5%
Name two common variations of the Circle of Willis.
Having a large anterior communicating artery
Having one large posterior communicating artery and one small one
What artery supplies the caudate (ACA, MCA or PCA)?
ACA (deep branches)
What artery supplies the putamen and globus pallidus (ACA, MCA or PCA)?
MCA
What artery supplies the thalamus (ACA, MCA or PCA)?
PCA (deep branches)
What do the vertebral arteries supply? (2)
Spinal cord
Dorsal medulla of brainstem (PICA)
What does the basilar artery supply? (2)
Pons
Cerebellum
What does the posterior cerebral artery supply? (5)
Inferior and medial temporal cortex Inferior and medial occipital cortex Thalamus Posterior internal capsule Midbrain
Describe the venous drainage of the brain, and how CSF flows back into venous blood.
Superficial cerebral veins cross the subarachnoid space and pierce the dura as they enter intracranial (dural) venous sinuses.
Arachnoid granulations allow CSF to flow into venous blood of sinuses but prevent backflow of blood into sub-arachnoid space.
What are the major causes of stroke? (7)
Hypertension (36%) Head injury (trauma) Atherosclerosis Aneurysm (36%) Alcoholics Arteriovenous malformation (11%) Elderly
What are the two types of stroke?
Ischaemic stroke (71%) Cerebral/intracerebral haemorrhage (26%)
What are two causes for ischaemic stroke?
Atherosclerosis
Embolism
What are two causes for hemorrhagic stroke?
Trauma
Spontaneous
What can be seen in patients with a MCA stroke of the dominant hemisphere? (2)
Which arteries are often involved?
Global aphasia and sensorimotor loss on contralateral face, upper limb and trunk
Striate arteries
What can be seen in patients with a MCA stroke of the non-dominant hemisphere?
Neglect syndrome
What can be seen in patients with an ACA stroke? (4)
Contralateral sensorimotor loss below waist
Urinary incontinence
Personality defects
Split-brain syndrome
What can be seen in a patients with a PCA stroke? (3)
Contralateral homonymous hemianopsia
Reading and writing deficits
Impaired memory
What is a TIA?
A transient ischaemic attack, causing a temporary loss of brain function for less than 30 minutes. It comes on suddenly but resolves within 24 hrs.
Do all those who suffer TIAs have strokes?
No, but it is a warning sign of heart attack or stroke.
6% of patients who have TIAs have a heart attack/stroke in the first month, 12% in the first year and 27% in five years.
What are the symptoms of a TIA of the anterior circulation? (4)
Motor weakness
Hemi-sensory loss
Dysarthria
Transient monocular blindness
What are the symptoms of a TIA of the posterior circulation?
Vertigo
Diplopia
Ataxia
Amnesia
What is extradural/epidural haematoma characterised by in terms of clinical presentation?
May present with lucid period immediately after trauma, followed by unconsciousness (“talk and die” syndrome).
This is a rapid bleed, as it is arterial (or large venous sinus). As blood collects between the dura mater and the skull, it compresses intracranial structures and cranial nerve III.
What are the symptoms of an extradural haematoma? (2)
Weakness of extremities on contralateral side
Loss of visual field on contralateral side (due to compression of PCA)
How is an extradural haematoma diagnosed?
CT or MRI - a convex lense can be seen. The expansion stops at the sutures because the dura is tightly attached here.
What arteries are commonly implicated in extradural haematomas? (2)
Middle meningeal artery (temperoparital area, pterion)
Anterior ethmoidal artery (frontal)
What can cause a subdural haematoma? (2)
Where does the blood collect?
Trauma (acute or subacute) - high speed acceleration and deceleration
Ageing (chronic)
Between dura mater and arachnoid mater (subdural space)
What are the symptoms of a subdural haematoma? (5)
Irritability Seizures Headache Numbness Disorientation
How is a subdural haematoma diagnosed on CT? How are they differentiated from extradural haematomas?
A crescent shape with concave surface can be seen. They can also have a convex appearance so can look like extradural, BUT they can cross the suture lines (unlike extradural).
What vessels are implicated in subdural haematoma?
What does this mean in terms of the speed of the bleed?
Bridging veins Slower onset (venous bleed)
Where does the bleed occur in subarachnoid haematoma?
What causes this? (2)
Is it a venous or an arterial bleed?
Between arachnoid and pia mater (in the subarachnoid space)
Ruptured aneurysm or a head injury
Arterial
What are the symptoms of a subarachnoid haematoma? (4)
Severe headache
Vomiting
Confusion
Lowered level of consciousness
How is a subarachnoid haematoma diagnosed on CT?
White signal diffuse over sulci on both sides
How else might a subarachnoid haematoma be diagnosed?
Lumbar puncture - evidence of blood or bilirubin
What are the three types of cerebral aneurysms?
Saccular
Fusiform
Berry
Are men or women at higher risk of cerebral
aneurysms?
Women (3:2)
How many people develop a brain aneurysm?
1 in 15
Where are four likely places that aneurysms develop?
Between the ACA and the anterior communicating artery (40%)
Where the MCA branches (34%)
Where the ICA and posterior communicating artery connect (20%)
Where the basilar splits into the PCA (4%)
What artery is occluded in lateral medullary syndrome (Wallenberg syndrome)?
PICA
What are the symptoms of Wallenberg syndrome? (8)
Vertigo Nystagmus Nausea and vomiting Dysarthia Dysphonia Loss of pain and temp in body (contralateral) Loss of pain and temp in face (ipsilateral) Loss of gag reflex
What syndrome is associated with Wallenberg syndrome? On which side?
Horner syndrome (ipsilateral)
