Stroke

Major classifications of stroke

• Ischaemia-infarction – 80-85%
  • Thrombotic
  • embolic
• Intracranial haemorrhage -15-20%

 

• Pathology may be;
  • Due to disease of the vessel itself – eg artherosclerosis and subsequent thrombus formation
  • Reduced perfusion – shock, blood hyperviscosity
  • Embolism
  • Vascular rupture

 

• TIAs preceed thrombotic strokes in 50-75% of affected patient

 

Ischaemic stroke

 

• Subtypes;
  • Lacunar strokes
    • A result of hypertensive small vessel disease
    • Due to occlusion of penetrating branches of the circle of Willis, middle cerebral artery stem or vertebral and basilar arteries
  • Large vessel thrombotic strokes with low flow
    • May be due to a perfusion deficit
  • Embolic strokes
    • Cardiac mural thrombi are the most common sources, particularly from AF
    • Results in a higher risk of developing a haemorrhagic stroke, as the vessel walls downstream of the occlusion are weakened and restoration of perfusion can result in bleeding

 

• Other causes of ischaemic stroke
  • Fibromuscular dysplasia
  • Giant cell temporal arteritis
  • Hypercoagulable disorders

 

• Ischaemic cascade and secondary injury
  • Cells within ishaemic core are irreversibly damaged and will die
  • Surrounding this ischaemic core is the transitional zone where the cells are not yet irreversibly damaged
  • Cell death occurs due to;
    • Cells cant make ATP
    • The sodium-potassium pump fails resulting in neuronal swelling
    • Excitotoxicity via release of glutamate
    • NO production
    • Brain cells ultimately die through the actions of calcium activated proteases, lipases and free radical formation
    • Infracted brain swells and causes increased intracranial pressure
• Secondary damage can be caused by
  • Disruption of the BBB
  • Increased vascular permeability leading to cerebral oedema
  • Hyperperfusion zones surrounding ischaemic tissue can steal blood flow and hasten death of ishaemic cells
  • Loss of cerebral autoregulation

 

Haemorrhagic strokes

 

• May occur when intracerebral vascular lesions rupture
• Ischaemia can be a secondary consequence of haemorrhage due to;
• Pressure on blood vessels due to extravasation of blood into the fixed volume of the skull
• Reactive vasospasm of blood vessels exposed to free bleeding into the space between the arachnoid and pia mater
• Causes include;
  • Hypertension
  • Bleeding disorders
  • Over aggressive anticoagulation
  • Drugs – cocaine and amphetamine

 

• Intracerebral haemorrhage
  • Basal ganglia and internal capsule are commonly affected because of their location near the deep terminal arteries