Stroke | What Happens to the Brain When Blood Flow is Suddenly Interrupted?

An ischemic stroke is a cerebrovascular event characterized by the obstruction of a blood vessel supplying the brain. This blockage deprives brain tissue of oxygen and essential nutrients, leading to the rapid death of neurons, the fundamental cells of the nervous system. The obstruction is typically caused by a thrombus, a blood clot that forms within a cerebral artery, often at a site of pre-existing narrowing from atherosclerosis (a buildup of fatty plaques). Alternatively, the blockage can result from an embolus, which is a clot or piece of debris that travels from another part of the body—commonly the heart—and lodges in a smaller brain artery. The specific neurological deficits that manifest, such as difficulty speaking or limb weakness, directly correlate to the brain region affected by this sudden loss of blood flow. Without immediate medical intervention to restore circulation, the damage to the brain tissue can become permanent, resulting in long-term disability. This type of stroke accounts for the vast majority of all stroke cases and is a critical medical emergency.

A hemorrhagic stroke occurs when a blood vessel within the brain ruptures and bleeds into the surrounding tissue. This event disrupts brain function through two primary mechanisms. First, the area of the brain previously supplied by the ruptured artery is now deprived of blood, leading to ischemic injury similar to a blockage-type stroke. Second, the accumulating pool of blood, known as a hematoma, exerts direct physical pressure on the brain tissue, compressing and damaging neurons. Furthermore, the blood itself is toxic to brain tissue, initiating an inflammatory response that can cause secondary injury and swelling (edema), which further increases intracranial pressure. The most common cause of hemorrhagic stroke is uncontrolled hypertension (high blood pressure), which weakens artery walls over time, making them susceptible to bursting. Another significant cause is the rupture of a cerebral aneurysm, a weak, bulging spot on an artery wall. Hemorrhagic strokes are less common than ischemic strokes but are often more severe and have a higher mortality rate.

The immediate signs of a stroke are best recognized using the F.A.S.T. acronym, which simplifies the identification of this medical emergency. 'F' stands for Face Drooping: one side of the face may droop or feel numb, resulting in an uneven smile. 'A' stands for Arm Weakness: one arm may be weak or numb, and when both arms are raised, one may drift downward. 'S' stands for Speech Difficulty: speech may be slurred, incoherent, or the person may be unable to speak or understand what is being said. 'T' stands for Time to call emergency services: immediate medical attention is critical upon observing any of these signs. Time is a crucial factor in stroke treatment, as interventions are most effective when administered quickly, minimizing the extent of brain damage.

A stroke typically affects one side of the body due to the brain's contralateral organization. This neuroanatomical principle means that the right cerebral hemisphere controls the muscles and processes sensory information from the left side of the body, while the left cerebral hemisphere controls the right side. Since a stroke is a focal event that damages a specific area in one hemisphere, the resulting motor and sensory deficits manifest on the opposite side of the body. For example, a stroke in the motor cortex of the left hemisphere will lead to paralysis or weakness (hemiplegia or hemiparesis) on the right side of the body. This contralateral control is a fundamental aspect of how the brain is wired to the rest of the body.

Yes, women face unique risk factors for stroke that are not present in men. Hormonal fluctuations and physiological changes throughout a woman's life can increase her susceptibility. For instance, the use of certain types of hormonal birth control, particularly those containing estrogen, can slightly elevate the risk of blood clots, which can lead to an ischemic stroke. This risk is substantially amplified in women who smoke or have high blood pressure. Pregnancy is another period of increased risk due to physiological changes such as elevated blood pressure and increased stress on the heart, with conditions like preeclampsia being a significant risk factor. Furthermore, post-menopausal women who use hormone replacement therapy may also have a slightly increased risk. Atrial fibrillation, a type of irregular heartbeat that is a major cause of stroke, is also more common in older women than in older men. Recognizing these gender-specific factors is crucial for accurate risk assessment and preventive care.