The stroke can be defined as a sudden impairment of brain functions, which is caused by non-injury-related damage to brain cells. We distinguish ischemic and hemorrhagic strokes.
This stroke is caused by damage to the brain cells due to deficiency of oxygen (i.e. ischemia). Ischemic stroke constitute about 80% of all strokes. The mechanism is substantially similar to a heart attack. Arteries supplying brain with blood may be narrowed by the process of atherosclerosis (such as narrowed carotid arteries). The narrowing itself usually does not cause any symptoms but a sudden rupture of the atherosclerotic plate may cause formation of a blood clot that may either block the artery in place of its occurrence or the blood clot may be flow into the brain and obstruct a cerebral vessel. The part of brain supplied with blood from the affected artery suffers from ischemia and its cells begin to die. The fundamental difference from a heart attack is the extreme sensitivity of brain cells to the lack of oxygen. Myocardial cells can withstand severe ischemia for hours, brain cells only for several minutes.
As mentioned above, the major causative factor is atherosclerosis and its risk factors. In addition, it is necessary to mention atrial fibrillation as another important cause of ischemic strokes. Atrial fibrillation is a common arrhythmia that increases risk of occurrence of blood clots within heart atria and embolism of such blood clots to the brain vessels.
Both the atherosclerosis and carotid narrowing do not hurt and they are usually completely asymptomatic. The best prevention is healthy lifestyle including healthy diet and regular physical exercise. Sometimes, the stroke is preceded by a so-called transient ischemic attack (TIA), which is a temporary bout of ischemia. It is caused by a short-time obstruction of a brain vessel by a blood clot, which is quickly dissolved causing only temporary symptoms. TIA can manifest in many ways, for example by losing sight in one eye, muscle paralysis or tingling sensations in extremities, sudden trouble with speaking, etc. The condition quickly returns to normal but later, it ay be followed by a full scale stroke with permanent consequences.
Hemorrhagic stroke accounts for about only 20% of all strokes. The bleeding is directly caused by a rupture of a blood vessel in the brain; blood flows out and mechanically damages the adjacent brain tissue. The most common reason is a long-term uncontrolled high blood pressure, which damages small cerebral arteries. Sometimes, the bleeding can occur from pouch-like dilated arterial aneurysms. These brain aneurysms can be congenital or acquired during a person's life. In many people they are asymptomatic for their whole life but sometimes they can rupture causing acute brain hemorrhage.
The symptoms of both conditions are more or less similar. Strokes manifest with muscle paralysis, headache, vomiting, dizziness, loss of consciousness, behavioral changes, impaired vision, double vision, speech disorders and sometime even convulsions.
The diagnosis is usually done by combination of computed tomography of brain and neurological examination. The neurologist diagnoses neurological symptoms in both types of strokes, while computed tomography is great in confirming intracerebral hemorrhage. Ischemic stroke in its acute phase often has a completely normal CT finding. Further investigation depends on the individual case, but in general every patient with an ischemic stroke should have done at least ECG (to exclude atrial fibrillation) and ultrasound of carotid arteries (to exclude their narrowing).
Ischemic strokes are usually treated conservatively by adequate hydration (dehydration can considerably enlarge the damaged area) and administration of anticoagulation drugs. In some cases, it is possible to administer special thrombolytic agents, i.e. drugs that directly dissolve the thrombus. However, such drugs must be cautiously indicated as they can have serious hemorrhagic side-effects.
Hemorrhagic strokes are usually treated by bed-rest and cautious monitoring of blood pressure. Brain aneurysms can be also treated surgically (clipping) or endovascularly (coliling).