Stroke Pathophysiology and Infarction Causes

Stroke

• A stroke is an acute brain abnormality caused by a vascular process.
• Infarction occurs when blood flow to an area of the brain is interrupted, causing brain tissue to die.
• Causes of Infarction:
  • Thrombotic infarction: A blood clot forms in a cerebral artery, blocking blood flow.
  • Embolic infarction: A blood clot travels from another part of the body to the brain, blocking a cerebral artery.
  • Lacunar infarction: A small infarct occurs in a deep brain structure, often caused by a blood clot in a small artery.
  • Global injury: A widespread lack of oxygen and blood flow to the brain, often due to cardiac arrest or severe hypotension.
• Clinical features of cerebral infarctions:
  • Neurological deficits depend on the location and severity of the infarct.
  • Common symptoms include weakness, paralysis, numbness, speech problems, and vision loss.
• Evolution of Infarction:
  • 12-24 hours: Microscopic changes like "Red Neurons" and a few neutrophils are visible.
  • 2-3 days: A blurring of the grey/white matter junction, severe oedema, and liquefaction are visible macroscopically.
  • 10-21 days: Oedema fades, and gliosis begins.
  • Months to years: A thin-walled cyst formed, filled with glial fibres.
• Molecular events in Cerebral Ischaemia:
  • Depletion of oxygen and glucose, leading to reduced ATP production.
  • Activation of ion channels, causing an influx of sodium and calcium, leading to cell swelling and neurotransmitter release.
  • Release of free radicals, damaging cell membranes and increasing inflammation.
  • Lactic acidosis due to anaerobic metabolism from ischaemia.
• Haemorrhage occurs when a blood vessel in the brain ruptures, causing bleeding.
• Types of Haemorrhage:
  • Extradural: Bleeding between the skull and the dura mater, usually caused by a skull fracture that tears an artery.
  • Subdural: Bleeding between the dura mater and the arachnoid mater, commonly caused by a tear in a vein.
  • Subarachnoid: Bleeding within the subarachnoid space, often caused by a ruptured berry aneurysm.
  • Intracerebral: Bleeding within the brain tissue itself, often due to hypertension, aneurysms, or trauma.

Neurodegenerative Diseases

• Alzheimer's Disease (AD):

  • Affects 30 million people worldwide, including 250,000 Australians.
  • Accounts for 10% of people over 65 and 50% of those over 85.
  • The most common cause of dementia.
  • Pathophysiology:
    • Amyloid beta plaques: Abnormal protein fragments accumulate outside neurons.
    • Neurofibrillary tangles: Abnormal protein filaments (tau) accumulate inside neurons.
    • These accumulations disrupt brain function and lead to neuronal death.
  • Clinical signs and symptoms:
    • Memory loss, confusion, disorientation, and difficulty with language and problem-solving.
    • Personality changes are often the first sign in frontotemporal dementia.
  • Diagnosis:
    • Based on clinical assessment, history, and physical examination.
    • Mental status tests like the Mini-Mental State Examination (MMSE) are used.
  • Treatment:
    • No cure, but medications help manage symptoms.
    • Disease-modifying therapies are being developed to slow or halt the progression of the disease.

• Parkinson's Disease (PD):

  • A chronic and progressive neurological disorder that affects movement.
  • Epidemiology:
    • The prevalence of Parkinson's Disease is increasing, affecting approximately 1% of the population over the age of 60.
  • Pathology:
    • Aetiology: The exact cause is unknown, but it's thought to be a combination of genetic and environmental factors.
    • Pathophysiology: Degeneration of dopamine-producing neurons in the substantia nigra, a region in the brain involved in movement control.
    • Clinical features:
      • Resting tremor: A rhythmic shaking of the limbs.
      • Bradykinesia: Slowness of movement.
      • Rigidity: Stiffness of muscles.
      • Postural instability: Difficulty maintaining balance.
  • Treatment:
    • No cure, but medications can improve symptoms and quality of life.
    • Deep brain stimulation (DBS) can be used to treat severe motor symptoms.
    • Lifestyle interventions, such as exercise and a healthy diet, can be beneficial.

Meningitis

• Meningitis is an inflammation of the meninges, the membranes surrounding the brain and spinal cord.
• Causes:
  • Bacterial meningitis: Caused by bacteria, such as Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae.
  • Viral meningitis: Caused by viruses, such as enteroviruses, herpes viruses, and arboviruses.
  • Fungal meningitis: Caused by fungi, such as Cryptococcus neoformans.
• Symptoms:
  • Fever, headache, stiff neck, nausea, vomiting, sensitivity to light, confusion, and seizures.
• Diagnosis:
  • Based on clinical examination, medical history, and laboratory tests, including lumbar puncture to analyze cerebrospinal fluid.
• Treatment:
  • Treatment depends on the underlying cause and can include antibiotics for bacterial infections, antiviral medications for viral infections, and antifungal medications for fungal infections.
  • Vaccines are available for some types of bacterial meningitis.
• Complications:
  • Brain damage, hearing loss, seizures, and death.
  • Hydrocephalus (accumulation of fluid in the brain), can occur.

This quiz covers the critical aspects of stroke, including the types of infarction, their causes, and clinical features. Test your understanding of how different factors lead to brain damage and the neurological outcomes associated with cerebral infarctions.