When blood supply to the brain is compromised, it can lead to damage, and possibly death, of the brain cells, a condition called stroke.
THE human brain has been compared to a supercomputer. But the brain is much more complicated than that, a fact that is confirmed with each new discovery about its capabilities, which is still largely unknown.
This single organ controls all the body’s functions, which include heartbeat, breathing, sexual function, thinking, speech, memory, emotions, movement, and sleep. It influences the immune system’s response to ill health, and determines, to some extent, how a person responds to medical treatment.
In short, the brain makes us human and separates us from other living creatures on planet Earth.
The brain, which is encased in the bony skull, is divided into two sides (hemispheres), each controlling the opposite side of the body.
Different parts of the brain have different functions. The frontal lobe is responsible for the highest intellectual functions like thinking and problem-solving. The parietal lobe is responsible for sensory and motor function. The hippocampus is involved in memory. The thalamus is the relay station for almost all of the information coming into the brain, and the hypothalamus, the relay stations for the systems regulating the body’s functions.
The midbrain has cells that relay specific sensory information from the sense organs to the brain. The hindbrain comprises the pons and medulla oblongata, which control breathing and heart functions, and the cerebellum, which controls movement and cognitive processes that require precise timing.
The brain’s functions depend on a constant blood supply for the oxygen and nutrients needed by its cells. The restriction or stoppage of this supply leads to damage, and possibly death, of the brain cells. This is called a stroke.
A stroke, also called a cerebrovascular accident (CVA), is a condition whereby the blood supply to a part of the brain is cut off. It is a medical emergency, and the earlier treatment is provided, the less severe it will be.
Strokes are the third most common cause of death in Malaysia. It is estimated that there are about 52,000 strokes per annum, i.e. strokes occur in six persons every hour.
There are two main types of strokes.
Ischaemic strokes, which comprise the majority of stroke cases, occur when the blood supply to the brain stops because the vessel is blocked by a blood clot. This may be due to thrombosis, in which a blood clot forms in one of the brain’s arteries, or to an embolism, in which a blood clot formed elsewhere in the body gets into the brain’s arteries to reach a blood vessel small enough to block its passage.
Haemorrhagic strokes occur when bleeding results from a burst blood vessel supplying the brain because of weakness in its wall. The blood collection compresses the brain, causing damage and loss of function.
A related condition is transient ischaemic attack (TIA) in which there is temporary interruption of the blood supply to part of the brain, leading to a “mini-stroke”. As TIAs provide a warning that a stroke is on the way, they should be treated seriously.
Causes of stroke
Strokes are preventable as lifestyle changes can reduce many of the risk factors. However, there are some risk factors that are not preventable. They include:
·Age – The risks are increased in the older person, although about a quarter of strokes occur in the young.
·Ethnicity – The risks are increased in Indians and Malays because the incidence of diabetes and hypertension are higher in these groups.
·Medical history – The risks are increased if one has had a heart attack, stroke, or TIA.
·Family history – The risks are increased if a close relative has had a stroke.
Ischaemic strokes occur when the brain’s blood supply is blocked by clots formed where the arteries are narrowed or blocked by cholesterol deposits due to atherosclerosis.
Everyone’s arteries get narrower with age, but the process is hastened by factors like high blood pressure, poorly controlled diabetes, raised blood cholesterol, smoking, excessive alcohol intake, obesity and a family history of diabetes or heart disease.
An irregular heartbeat leads to blood clots being thrown off to block the brain’s blood supply. The causes of irregular heartbeats include high blood pressure, coronary artery disease, disease of the heart’s mitral valve, overactive thyroid gland and excessive alcohol intake.
Haemorrhagic strokes occur when a blood vessel of the brain bursts, resulting in bleeding into the brain itself (intracerebral haemorrhage). Sometimes, the bleeding is on the brain surface (subarachnoid haemorrhage).
The primary cause of haemorrhagic stroke is high blood pressure, the risk factors of which include smoking, overweight or obesity, lack of exercise, excessive alcohol intake and stress.
Blood-thinning medicines can also cause haemorrhagic strokes, which can also occur from blood vessel malformations in the brain or an aneurysm, which is a balloon-like swelling of a blood vessel.
Trauma can also cause bleeding in the brain. Although the cause is usually apparent, bleeding into the brain’s lining (subdural haematoma) may occur without signs of trauma.
A rare cause of stroke is blood clot formation in the brain’s veins, which is usually due to clotting abnormalities.
Signs and symptoms
The features vary depending on the part of the brain that is affected and the extent to which it is affected. Strokes usually occur suddenly.
The common features are:
·Face – There may be an inability to smile, open the mouth or the face or eye may hang downwards.
·Arms – There may be an inability to lift one or both arms due to numbness or weakness.
·Legs – There may be an inability to move one or both legs due to numbness or weakness.
·Speech – There may be slurring of speech or an inability to talk at all.
Other features may include sudden vision loss, dizziness, difficulty talking and understanding what others say, difficulty swallowing, balancing problems, sudden and severe headache, and blacking out.
Awareness of the above features is crucial, particularly for those at increased risk of a stroke, and their caregivers.
The complications of stroke include swallowing problems (dysphagia), which affect about a third of stroke patients. This leads to small food particles entering the respiratory tract causing lung infection (pneumonia).
Stroke can also lead to excess cerebrospinal fluid (CSF) in the brain’s ventricles (hydrocephalus) in about 10% of haemorrhagic strokes. CSF, which is produced by the brain, is continuously drained away and absorbed by the body. When its drainage is stopped following a haemorrhagic stroke, the excess CSF causes headaches, loss of balance, nausea and vomiting.
A small percentage of stroke victims who have lost some or all movement in their legs will have blood clot formation in their legs. The features of this deep vein thrombosis (DVT) include swelling, pain, tenderness, warmth and redness, especially in the calf. Urgent diagnosis and treatment is necessary to avoid the clot moving to the lungs, causing pulmonary embolism, which is potentially fatal.
The diagnosis of a stroke is made by history taking and physical examination. However, imaging of the brain is essential to determine if it is an ischaemic or haemorrhagic stroke, the part of the brain that is affected, and the severity of the stroke.
As the treatments of the different types of stroke vary, a speedy diagnosis will facilitate its management.
The common methods of brain imaging are computerised tomography (CT) scans and magnetic resonance imaging (MRI).
The CT scan involves multiple x-ray imaging to produce detailed three-dimensional images of the brain. MRI involves the use of magnetic and radio waves to produce detailed images of the brain.
Both the CT scan and MRI are used to take images of the brain’s blood vessels, as well as the blood vessels in the neck that connect the heart and the brain’s blood vessels. This procedure, called a CT or MR angiogram. involves injecting a dye into a vein in the arm.
The brain imaging modality used depends on the availability of a CT scan and/or MRI. A CT scan provides enough information if the suspected stroke is major. The MRI is useful if there are complex symptoms, the extent or location of the affected area is unknown, and in patients who have recovered from a TIA.
Brain imaging should be done early; in some patients, within an hour of admission.
A swallow test is usually done for all stroke patients because of the risk of aspiration pneumonia due to dysphagia. This involves giving a few teaspoons of water to the patient and if there is no choking or coughing, to be followed by half a glass of water.
Other investigations of the cardiovascular system will be carried out to determine the cause of the stroke.
It includes ultrasound examination of the heart (echocardiogram) or carotid artery in the neck (Doppler scan). It can also include injecting dye into the carotid or vertebral arteries (arteriography) to enable a detailed examination of the arteries in the brain.
The management of stroke will be discussed in a subsequent article.
Source: Dr Milton Lum