Curriculum · Neurology
Ischaemic stroke
What it is
Stroke is ischemic more commonly than hemorrhagic: 80% ischemic, 20% hemorrhagic.
Causes and risk
Acute blockage of a vessel disrupts blood flow, and the ischemia that follows ends in liquefactive necrosis. Irreversible damage begins after 5 minutes of hypoxia, and irreversible neuronal injury is what is left. The most vulnerable tissue is named: hippocampus, neocortex, cerebellum with its Purkinje cells, and the watershed areas, with the hippocampus the most vulnerable of all to ischemic hypoxia.
Three types are separated by what blocks the vessel.
- Thrombotic, from a clot forming directly at the site of infarction, commonly the MCA, usually over an atherosclerotic plaque.
- Embolic, where an embolus from another part of the body obstructs the vessel and can affect multiple vascular territories. The examples given are atrial fibrillation, carotid artery stenosis, and DVT with patent foramen ovale.
- Hypoxic, from hypoperfusion or hypoxemia, common during cardiovascular surgeries and it tends to affect watershed areas.
A fourth name appears elsewhere for the same split: thrombotic, embolic and lacunar, the last being a small terminal artery occlusion. Atrial fibrillation is called an important risk factor for an embolic stroke, particularly when anticoagulation therapy is taken noncompliantly.
The tissue changes run to a clock. At 12-24 hours the histologic features are eosinophilic cytoplasm with pyknotic nuclei, the red neurons; at 24-72 hours necrosis with neutrophils; at 3-5 days macrophages, the microglia; at 1-2 weeks reactive gliosis by astrocytes with vascular proliferation; and after 2 weeks a glial scar.