Stroke
What is a stroke?
Acute loss of perfusion to vascular territory of the brain, resulting in ischemia and a corresponding loss of neurologic function
Classification
Haemorrhagic
Ischemic
10-15%
Higher mortality rate
Treatment is supportive only
Causes
Thrombosis
Embolism
Hypoperfusion
Result of rupture of atherosclerotic plaque in the intracranial arteries
Activates platelet adhesion and clotting cascade to form occlusive thrombus
Typically from thrombus in heart of break off from atheroaclerotic plaques in the carotid arteries
Ischaemic cascade
Within sections to minutes of the loss of glucose + oxygen delivery to neurons, the cellular ischaemic cascade begins and neurons cease to function
Normal electrophysiological function of the cells stops
Neuronal and glial injury produced oedema in the hours post stroke -> further injury to surrounding tissues
Clinical presentation
Anterior cerebral artery occlusions
Primarily affect frontal lobe function
Disinhibition and speech perseveration
Primitive reflexes (e.g. grasping, sucking)
Altered mental status
Impaired judgement
Contralateral weakness (greater in legs than arms
Contralateral cortical sensory deficits
Gait apraxia
Urinary incontinence
Middle cerebral artery occlusions
Contralateral hemiparesis
Contralateral hyperasethesia
Ipsilateral hemianopia
Gaze preference toward the side of the lesion
Agnosia
Receptive or expressive aphasia
If lesion occurs in dominant hemisphere
Rarest type of stroke
Neglect and inattention
Non-dominant hemisphere lesions
Weakness of the arm and face usually worse than lower limb
MCA supplies the upper extremity motor strip
Posterior cerebral artery occlusions
Vision and thought affected
Cortical blindness
Homonymous hemianopia
Visual agnosia
Altered mental status
Impaired memory
Ishcaemic Pneumbra
In acute stroke, ischaemia is more often incomplete, with the injured area of the brain receiving a collateral blood supply from uninjured arterial and leptomeningeal territories
Therefore results in central irreversibly infarcted tissue core surrounded by peripheral region of stunned cells with reduced blood supply (pneumbra)
Evoked potentials in the peripheral region are abnormal and cells have ceased to function, but this region is potentially salvageable with early revascularisation
Detection of ischaemic signs on non-enhanced CT
Main finding is abnormal cortical-subcortical area within a vascular territory
Area is typically darker (hypoattenuation) than normalbrain due to oedema
Extent of hypoattenuating area is crucial
Presence in >1/3 of the MCA territory is a contraindication for revascularisation because of haemorrhagic complications
Has relatively low sensitivity in first 24 hours (especially within the limited 3-6 hour time window for thromblytic treatment)
Subtle signs include:
Hyperdense vessel sign (high density thrombus occluding middle cerebral artery)
Innability to visualise the left lentiform nucleus due to cytotoxic oedema (may be seen within first 2 hours of symptoms)
Using MRI
T1 is best for anatomic delineation
T2 shows fluid (e.g. CSF and oedema) as bright white
FLAIR (fluid attenuated inversion recovery) - by signal manipulation, free fluid (CSF) is dark whilst oedema may remain bright
Gradient echo sequence
Makes blood products very dark
The types of pulses can be altered in a multitude of ways in order to detect different pathological findings
More specific and sensitive than CT for the detection within first few hours after onset
Has additional benefit of depicting the pathologic entity (stroke and its minics) in multiple planes
Typical MRI findings include hyperintense (brighter than normal) signal in white matter on T2-weighted images and fluid-attenuated inversion recovery images, with a resultant loss of gray-matter-white-matter differentiation on T1 weighted imaging analogues
Newer MRI sequences e.g. diffusion weighted imaging (MWI) have been proven to be very sensitive to hyperacute strokes
Underlying principles
Normal mortion of water molecules in living tissues is random
In stoke, homeostasis is altered (intracellular vs extracellular)
Extracellular water accumulation (cytotoxic oedema) with a decreased rate of extracellular diffusion within the affected tissue
On diffusion-weighted images, ischaemic tissue appears bright in comparison with normal brain tissue
Faster, readily available, easy to interpret
Perfusion CT (the future - identifying penumbra)
Iodine based fluid injected
Infarcted core shows almost no blood flow however penumbra shows less than normal brain but more than infarcted core