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Red neurons
6%
13/234
Necrosis and neutrophils
3%
7/234
Macrophages
2%
5/234
Reactive gliosis and vascular proliferation
31%
72/234
Cyst formed by astrocyte processes
58%
135/234
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By approximately one month after an ischemic infarct, the involved area will have formed a glial scar, which histologically appears as a cyst formed by astrocyte processes. Ischemic strokes rapidly cause irreversible hypoxic damage to neurons. Due to their high metabolic demand, neurons are extremely sensitive to ischemia and just five minutes of hypoxia can trigger irreversible damage and lead to cell death. Neuronal cell death from ischemic stroke initiates the process of reactive gliosis, a process which ultimately culminates in the formation of glial-scarring. Reactive gliosis involves a sequence of histologically distinct steps. Within 12 - 28 hours red neurons are seen; 24 - 72 hours shows necrosis and neutrophilic infiltration; after 2 - 3 days macrophages predominate; in 1 - 2 weeks vascular proliferation and reactive gliosis is seen; finally after 2 or more weeks a glial scar has formed. Yew et al. review the types of stroke. Stroke can be broadly divided into hemorrhagic and ischemic stroke. This distinction is clinically important because ischemic strokes can be treated with thrombolysis. 87% of strokes are ischemic. Clinical distinction of stroke type is not reliable. To reliably differentiate between stroke types, CT imaging of the head is used. CT can reliably rule out hemorrhagic stroke and mass effect under most circumstances. MRI imaging is more useful in detecting ischemic stroke and can be obtained if there is any question of etiology on CT. Huang et al. review the process of glial scar formation following ischemic stroke. Uncontrolled death of neurons promotes significant inflammatory response, which can lead to collateral damage to adjacent neurons. Such injuries stimulate reactive gliosis, the process by which astrocytes form a scar around the area of injury to control and limit the immune response that would otherwise occur. However, scar formation also prevents axon regeneration and thus limits recovery in the chronic phase. Illustration A is a micrograph depicting reactive gliosis following ischemic CNS injury. Incorrect Answers: Answer 1: Red neurons predominate 12 - 48 hours post infarction. Answer 2: Neutrophilic infiltration and necrosis predominates 24 - 72 hours post infarction. Answer 3: Macrophages predominate 2 - 3 days following ischemic stroke. Answer 4: Reactive gliosis and vascular proliferation is typically found 1 - 2 weeks post infarction.
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