A stroke occurs when there is an interruption of blood flow to the brain, which can happen due to ischemia or hemorrhage. When ischemia occurs, it means that a part of the brain is not receiving adequate blood supply, leading to oxygen deprivation and eventual brain tissue death, known as infarction. This event is primarily caused by blockages in blood vessels, often due to a clot or plaque buildup.
While a hemorrhage in the brain is also a cause of stroke, it is categorized as a type of stroke known as hemorrhagic stroke. In contrast, the question specifically asks for the physiological event that typically leads to a stroke in a general sense, where ischemic strokes (caused by blockage) are more common than hemorrhagic strokes (caused by bleeding).
Sudden head injuries may lead to strokes, particularly through resulting bleeding, but they are not an intrinsic cause of stroke in itself. Severe dehydration can cause various health issues but does not directly lead to a stroke. Therefore, the emphasis on ischemia leading to infarction is accurate as it captures the underlying mechanism of the most prevalent type of stroke, reinforcing its importance in understanding stroke pathology.