Circulatory system and stroke Flashcards
Circle of Willis
the joining area of several arteries at the bottom (inferior) side of the brain - the internal carotid arteries branch into smaller arteries that supply oxygenated blood to over 80% of the cerebrum
Anastome
connections b/w different cerebral arteries on cerebral surface - helps limit extent of cortical damage in stroke BUT creates vulnerability in “border zones/watershed areas” between arteries as they are the most distant portions of blood supply
Two kinds of Cerebrovascular accident (CVA) (a.k.a. stroke)
Ischemic stroke - when a blood vessel supplying the brain becomes blocked by blood clot, resulting in reduced oxygen
- Thrombotic strokes - caused when a blood clot forms in an artery leading to the brain
- Embolic strokes begin with a clot forming elsewhere in the body that breaks loose and travels to the brain.
Hemorrhagic stroke - when a blood vessel bursts, leaking blood into the brain.
Cerebrovascular accident (CVA) (a.k.a. stroke)
- can cause seizures d/t scar tissue
- can cause depression in 30% more left-sided CVAs
- function usually improves but can show worsening deficits d/t cerebral edema (swelling)
Ischemia vs. infarct
Ischemia - blood flow to tissue has been decreased, resulting in hypoxia
Infarction - goes one step further, means blood flow has been completely cut off resulting in necrosis/cellular death
3 main cerebral arteries
Anterior cerebral artery
Middle cerebral artery
Posterior cerebral artery
Anterior cerebral artery (ACA)
Supplies:
Surface - cortex on the anterior medial surface, from the frontal to the anterior parietal lobes including medial sensorimotor cortex (sensory for lower extremity)
Deep - head of caudate, anterior putamen, globus pallidus, internal capsule
Clinical syndromes (infarcts/blockages are uncommon)
1. Usually produce contralateral lower extremity cortical sensory loss and weakness of the upper motor neuron
2. Alien hand syndrome = damage to supplementary area, semiautomatic movements of contralateral arm not under control
3. Frontal lobe dysfunction - impaired judgement, indecisiveness, flat affect, pseudobulbar palsy (inability to control face movements)
4. Bilateral occlusion = apathy, confusion, and mutism
Grasp reflex
can also produce diencephalic amnesia (resulting in confabulation)
Middle cerebral artery (MCA)
most common infarcts and ischemic events
Supplies:
Surface - most of the dorsolateral cortex (involving frontal, parietal, and temporal lobes)
Deep: basal ganglia, internal capsule
Clinical syndromes (infarcts/ischemic events more common than ACA and PCA because of larger territory)
1. Left hemisphere lesions - contralateral hemiparesis, hemi-sensory loss, homonymous hemianopia, aphasia, apraxia
2. Right hemisphere lesions - hemi-attention, anosagnosia, dysprosody, possible apraxia
3. MCA watershed area affected: transcortical aphasia or global aphasia
Anterior: Broca’s aphasia
Posterior: fluent aphasia
Angular gyrus syndrome - fluent aphasia, Alexia with agraphia, Gerstmann’s syndrome
Infarcts occur in three areas:
- Superior division - supplies cortex above Sylvia fissure/lateral sulcus
- Inferior division - supplies cortex of lateral temporal and occipital lobes lobes below Sylvian fissure and part of lateral cortex
- Deep territory - includes internal capsule and much of the BG
MCA = gaze preference TOWARD lesion
Posterior cerebral artery (PCA)
Supplies:
Surface - inferior and medial temporal cortex, occipital cortex (including visual cortex)
Deep - thalamus
Clinical syndromes:
1. Typically causes contralateral homonymous hemianopia
2. Smaller vessels may lead to infarct of thalamus/posterior limb of internal capsule:
- contralateral sensory loss, hemiparesis, and/or homonymous hemianopia
- Thalamic aphasia (if in language dom hemisphere) - lexical-semantic deficits and intact word repetition
- Alexia without agraphia if involve left occipital cortex
What is a watershed infarct?
stroke caused by a drop in circulating pressure and or volume that results in critical ischemia or infarction between territories
Constitute approximately 10% of all cerebral infarcts
Locations:
- Between ACA and MCA: in frontal cortex extending from anterior horn to the cortex
- Between MCA and PCA: in parieto-occipital region extending from posterior horn to the cortex
- Parallel parafalcine stripes in subcortical white matter at the vertex suggests profound hypoperfusion (reduced blood flow)
Left MCA superior division infarct
- Broca’s aphasia
- Right face and arm weakness of the upper motor neuron type (sometimes sensory loss may be present)
- Impaired working memory and executive function deficits.
Visual field cut is usually absent.
Limb apraxia may be seen in the right arm after resolution of paresis, and/or in the left arm.
Left MCA inferior division infarct
- Wernicke’s aphasia
- Right visual field deficit
There may also be right face and arm cortical-type sensory loss, limb apraxia, and parts of Gerstmann’s syndrome (agraphia, acalculia due to conceptual difficulty, right-left disorientation, finger agnosia).
Motor findings are usually absent but mild right-sided weakness may be present, especially at onset.
Left MCA deep territory infarct
Right pure motor hemiparesis (weakness) of the upper motor neuron type.
…effect internal capsule
Larger infarcts may produce “cortical” deficits, such as aphasia.
Left MCA stem (initial part of the MCA is a single vessel called the stem)
Combination of left MCA infarcts +
- right hemiplegia
- right hemianesthesia (loss of tactile sensation)
- right homonymous hemianopia
- global aphasia
Left gaze preference
Right MCA superior division infarct
- Left face and arm weakness of the upper motor neuron type
- Impaired working memory and executive functions.
- Left hemineglect is present to a variable extent.
- May also be some left face and arm cortical-type sensory loss.
Right MCA inferior division infarct
- Profound left hemineglect.
- Left visual field and somatosensory deficits are often present
- Motor neglect with decreased voluntary or spontaneous initiation of movements on the left side can also occur.
- Some mild, left-sided weakness and right gaze preference may be present especially at stroke onset.
- There may also be anosognosia and visuospatial deficits characterized by Impaired visuospatial skills and writing, reading and arithmetic problems due to neglect and spatial difficulties
Right MCA deep territory infarct
- Left pure motor hemiparesis of the upper motor neuron type.
…because of internal capsule - Larger infarcts may produce “cortical” deficits, such as left hemineglect and visuospatial deficits as well, emphasizing the importance of larger circuits.
Deep territory infarcts produce…
contralateral motor hemiparesis
…because of internal capsule
Right MCA stem infarct
Combination of Right MCA infarcts+
- left hemiplegia,
- left hemianesthesia
- left homonymous hemianopia
- profound left hemineglect,
- visuospatial deficits
- anosognosia.
Right gaze preference
Left ACA infarct
- Right leg weakness of the upper motor neuron type
- Right leg cortical-type sensory loss.
Grasp reflex, executive function deficits, and transcortical motor aphasia can also be seen.
Larger infarcts may cause right hemiplegia.
Right ACA infarct
- Left leg weakness of the upper motor neuron type
- left leg cortical-type sensory loss.
Grasp reflex, executive function deficits, and left hemineglect can also be seen.
Larger infarcts may cause left hemiplegia.
Left PCA infarct
- Right homonymous hemianopia
- alexia without agraphia if extends to splenium (tail end) of corpus callous
Larger infarcts may cause:
- transcortical sensory aphasia
- right hemisensory loss
- right hemiparesis.
Verbal memory deficits may be present if the lesion extends to the left medial temporal lobe, especially the hippocampus.
Right PCA infarct
Left homonymous hemianopia.
Larger infarcts may cause:
- left hemisensory loss
- left hemiparesis.
Spatial memory deficits may be present if lesion extends to the right medial temporal lobe, especially the hippocampus.
