Strokes

---The word "stroke" suggests a sudden blow. Often, but now always, that is how strokes strike down their victims. The cause is brain damage due to blood blockage or leakage. More men than women suffer strokes, and over 60 is the most vulnerable age. All told, 2.5 million Americans (about 1 per cent of the population) have had their lives impaired by these so-called cerebrovascular accidents.

---Strokes come in three main kinds. In cerebral haemorrhage, a blood vessel bursts in the brain, the heart’s pumping action squirts blood into brain tissue, producing a clot that kills cells and maybe presses on the brainstem. Brain haemorrhage may happen if one of the brain’s blood vessels (among the body’s weakest) gets brittle, and bursts under abnormally high blood pressure, or when a weak spot in the wall of a vessel balloons out and bursts like a defective tire wall.

---Strokes are also caused by cerebral thrombosis and cerebral embolus. In cerebral thrombosis, a local clogging up of a blood vessel produces a thrombus (clot) blocking the vessel. The brain is denied of glucose and oxygen usually supplied by that vessel; brain cells deprived in this way quickly die and cannot be replaced. The same thing happens with cerebral embolus (plug). A plug of material gets stuck in a narrowed blood vessel. In fact, most strokes happen when a clot blocks a cerebral artery.

---Symptoms of a stroke range from brief confusion, dizziness, or slurred speech (a transient ischemic attack, where a blood vessel is only temporarily blocked) to throbbing headache, vomiting, numbness of limbs, partial paralysis, or coma. Damage done depends on the part and amount of brain affected. A huge fast-growing clot pressing on the brain, or swelling due to the death of many brain cells, affects the brainstem, causing coma and death if not treated. Blockage of the right middle cerebral artery may produce a massive so-called "President’s stroke" paralysing the left side of the body. Yet if brain damage affects only part of the right parietal lobe, the patient may seem normal except for visuospatial problems, for instance thrusting an arm in a pants leg when dressing. But strokes often affect gait, hearing, speech or vision.

---Luckily, treatment for stroke victims has vastly improved. CAT scans, X-ray angiograms that make blood vessels "glow" and other tests help surgeons to identify and localise damage. Aided by microscopes, microneedles, and microsutures, they can often clear clots or use a synthetic blood vessel to bypass a blocked internal carotid artery. Drugs also have parts to play: controlling blood clotting; lowering high blood pressure; or, with vasodilators, expanding blood vessels to prevent major strokes in patients who have had transient ischemic episodes.

---After someone has survived a serious stroke, physiotherapy can often do much to prevent deformities such as foot drop. Also, signals blocked by a damaged neuron circuit may be re-routed eventually through others, so that patient slowly recovers lost faculties. The extent of recovery varies with age, health, and the type of damage the brain has sustained.

Cerebral Haemorrhage

---A weak or diseased spot in the wall of a blood vessel swells out and ruptures. Blood from the damaged area floods into the surrounding brain tissue and clots. The clot enlarges, as shown above, as blood continues to pour in, and eventually presses on the brain.

Cerebral Thrombosis

---A blood clot (thrombus) forms in a cerebral blood vessel. Blood flow to the brain is impaired and the area supplied by the blocked vessel is deprived of oxygen and glucose, resulting in the death of some brain tissue.

Cerebral Embolism

---A mass of abnormal material (embolus) blocks an artery supplying blood to the brain. Usually the embolus is a clotted piece of blood that has become detached from a thrombus in another part of the body. As with cerebral thrombosis, brain cells are deprived of oxygen and die.

Incidence of Strokes

---The probability of stroke increases with age. This is partly a result of the rapidly increasing incidence of arterial disease, especially hardening of the arteries (arteriosclerosis), with age. Asterioclerosis leads to the build up of clotted up blood on the inner walls of the arteries and eventually the formation of a thrombus. High blood pressure, a condition also common amongst older people, adds to the danger of a stroke both by making the rupture of a brain artery more likely and because of its association with arterial disease.

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