Types of Stroke and Basic Brain Anatomy

Types of Stroke

Ischemic Stroke

• Definition: Blocked artery reduces blood flow to the brain.
• Prevalence: More common than hemorrhagic strokes.
• Damage Factors: Affected brain regions and duration of reduced blood flow.
• Transient Ischemic Attack (TIA): Symptoms self-resolve within 24 hours, usually minimal long-term issues.

Hemorrhagic Stroke

• Definition: Artery in the brain breaks, creating a blood pool that damages the brain.

Brain Anatomy

Major Regions

• Cerebrum: Divided into two hemispheres, with cortexes featuring four lobes (frontal, parietal, temporal, occipital).
• Cerebellum: Below cerebrum, aids in muscle coordination and balance.
• Brainstem: Connects to spinal cord, regulates vital functions (heart rate, breathing, etc).

Lobe Functions

• Frontal Lobe: Movement, executive function (decision making).
• Parietal Lobe: Sensory information processing, spatial orientation.
• Temporal Lobe: Hearing, smell, memory, visual recognition (faces/languages).
• Occipital Lobe: Vision.

Brain Blood Supply

• Arteries: Left and right internal carotid arteries, left and right vertebral arteries form basilar artery.
• Middle Cerebral Arteries: Serve lateral frontal, parietal, and temporal lobes.
• Anterior Cerebral Arteries: Serve medial frontal and parietal lobes, connected by the anterior communicating artery.
• Posterior Cerebral Arteries: Serve occipital lobe, part of temporal lobe, and thalamus.
• Circle of Willis: Alternative circulation system for blood in case of blockage.

Mechanisms of Ischemic Stroke

Endothelial Cell Dysfunction

• Irritants: Tobacco toxins damages artery lining (tunica intima).
• Atherosclerosis: Plaque buildup (fat, cholesterol, proteins, calcium, immune cells) obstructs blood flow.
• Sudden Blockage: Small plaques are prone to rupture, form clots, causing sudden blockage.

Embolism

• Definition: Blood clot travels and lodges in smaller downstream artery.
• Causes: Atrial fibrillation, heart attack, atrial septal defect.

Lacunar Stroke

• Definition: Involves deep branches of middle cerebral artery, results in cysts (lakes) due to tissue damage.
• Causes: Hyaline arteriolosclerosis (hypertension, diabetes).

Watershed Infarct

• Definition: Global reduction in blood flow, “furthest downstream” tissues affected.
• Symptoms: Injuries at junctions of different blood supplies.

Consequences of Ischemic Stroke

• Ischemic Core: Likely tissue death.
• Ischemic Penumbra: Surrounding tissue may survive if blood flow is restored.
• Cellular Effects: Build-up of sodium and calcium causes cytotoxic and vasogenic edema.
• Swelling: Leads to brain herniation and potential life-threatening symptoms.

Stroke Symptoms

• Anterior/Middle Cerebral Artery: Numbness, muscle weakness.
• Broca’s/Wernicke’s Area: Slurred speech, difficulty understanding language.
• Posterior Cerebral Artery: Vision problems.
• FAST Acronym: Facial drooping, Arm weakness, Speech difficulties, Time (to seek help).

Diagnosis and Treatment

Diagnostic Tools

• Medical Imaging: CT, MRI, angiography with contrast.
• FLAIR MRI: Distinguishes new vs old strokes.

Treatment Strategies

• Thrombolytic Enzymes: TPA to activate clot-busting mechanisms (time-sensitive).
• Aspirin: Prevents new clots from forming.
• Surgical Procedures: MERCI (clot removal), suction removal.

Post-Stroke Management

• Risk Management: Quitting smoking, maintaining healthy blood pressure and cholesterol, managing diabetes.
• Surgical Interventions: Carotid endarterectomy, stenting for severe atherosclerosis.

Recap

• Ischemic Stroke: Caused by decreased arterial blood supply.
• Causes: Atherosclerosis, thrombus, embolus, or reduced global blood flow.
• Identification and Response: Immediate response to symptoms critical for minimizing damage. FAST acronym for symptoms.