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Ischemic Stroke ll: Pathophysiology

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An ischemic stroke develops when a blood vessel supplying the brain becomes blocked, usually by a blood clot.

This prevents oxygen and glucose from reaching brain tissue; without oxygen, cellular energy production fails within minutes.

The affected region develops an infarct core—a zone of dead cells.

Surrounding it is the penumbra—tissue that remains viable but is at risk.

Oxygen deprivation disrupts ion homeostasis, causing sodium and calcium to flood into cells.

Water follows, leading to cytotoxic edema. Excess calcium also drives glutamate release, excitotoxicity, and activation of enzymes that damage neurons.

Inflammatory cells then arrive, increasing injury and contributing to vasogenic edema, where fluid leaks into the extracellular space.

Together, these processes worsen brain damage and raise intracranial pressure.

The longer the blockage persists, the more the injury becomes irreversible.

Overview

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An ischemic stroke occurs when a cerebral blood vessel becomes obstructed, most often by a thrombus or embolus, interrupting the delivery of oxygen and glucose to brain tissue. Because neurons rely on continuous aerobic metabolism, energy failure begins within minutes of reduced perfusion. The region receiving the least blood flow becomes the infarct core, an area of irreversible cellular death. Surrounding this core lies the penumbra, a zone of hypoperfused but still viable tissue that is highly vulnerable to further injury.

Early Cellular Injury

Oxygen and glucose deprivation rapidly impair mitochondrial function, leading to depletion of adenosine triphosphate (ATP). Failure of ATP-dependent ion pumps disrupts ionic homeostasis, allowing sodium and calcium to accumulate intracellularly. Water follows sodium osmotically, producing cytotoxic edema. Rising intracellular calcium concentrations trigger excessive release of glutamate, which overstimulates NMDA receptors and propagates excitotoxicity. This process activates proteases, lipases, and other enzymes that degrade cellular structures and accelerate neuronal injury.

Inflammation and Vasogenic Edema

Within hours, inflammatory mechanisms intensify the damage. Microglia activate and peripheral immune cells migrate into the ischemic region. These cells release cytokines, reactive oxygen species, and matrix-degrading enzymes that further compromise the blood–brain barrier. As the barrier becomes permeable, plasma proteins and fluid leak into the extracellular space, producing vasogenic edema. This additional swelling raises intracranial pressure and further reduces cerebral perfusion, expanding the area of injury.

Progression and Therapeutic Importance

The extent of neuronal loss depends on the duration of vessel occlusion. If blood flow is not restored promptly, penumbral tissue undergoes irreversible infarction. Rapid reperfusion—through thrombolysis or mechanical thrombectomy—is therefore essential to salvage at-risk tissue and limit long-term neurological deficits.

Transcript

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Ischemic Stroke

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Cytotoxic Edema

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