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The Stroke Story

The term stroke is used to denote neurological dysfunction of the brain due to diseases of the blood vessels or the vascular mechanism. The World Health Organisation has defined stroke as rapidly developing clinical signs for localised, and at times more widespread, disturbance of the cerebral function lasting more than twenty-four hours or leading to death with no apparent cause other than that arising from dysfunction of the blood vessels. The other commonly used terms for stroke are phaliz, adhrang, lakwa or paralysis. Cerebrovascular disease or strokes are very common neurological disorders and every physician either at primary, secondary or tertiary health care level is required to render medical help to these patients. Every general physician needs to know something about strokes and should have the competence to recognise them and refer to specialists where there are reasonable prospects of successful medical treatment and facilities for surgical intervention. Stroke is the third most important cause after cancer and heart attack of morbidity and mortality in elderly population of a nation. Until a few decades ago, attitude of the medical fraternity and the government and other funding agencies toward strokes was quite negative. Accordingly there was disproportionate expenditure and expansion of services with relation to heart care. This was so as the research, developments and understanding of cerebrovascular disease (disease of the blood vessels supplying the brain) lagged behind the therapeutic goals. All this has changed now. Modern researches in the understanding of such disease have led to new methods of treatment which have very clearly changed the prospects of survival of stroke patients. Both mortality and morbidity have been reduced. These have resulted in significant changes in medical and public attitudes towards stroke. There is a need for continuous campaign to focus medical and public attention to the fact that a stroke victim, like the heart attack victim, needs urgent intensive care. There is very rightly an increasing budgetary demand to establish stroke units or centres with intensive care facilities for patients and research purposes.

Story of the various factors that lead to cerebrovascular disease has established beyond doubt that the best course to tackle the problem is primary prevention. Brief, passing ischaemic attacks are very important warning signals. Every transient ischaemic attack results in some damage to the nerves even if there are no clinical signs of any disturbance after twenty-four hours or earlier. It has been found that within five years of a passing attack, 35 per cent of the patients suffer a full-blown stroke. Even more significantly 50 per cent of these have their stroke within one month of their first attack. Therefore secondary prevention by treatment with drugs that reduce blood-clotting platelet formation or surgery is of immense value in order to avoid a full-blown stroke later.

Early diagnosis and management of acute stroke is as important and essential as of acute heart attack. There is plenty of evidence which shows that in the first few hours after stroke, part of the brain tissue is still viable and may be salvaged, thus improving the outcome for the patients. Advances in imaging techniques by CT  scan or magnetic resonance imaging (MRI) have greatly benefitted the management of stroke. The minute anatomical details provided by MRI convey precise information about the network of blood vessels in the brain. During the first few hours after the event, there are continuous changes in the brain tissue around the damaged area. These are changes in blood flow metabolism, amino acid concentration and other parameters. These are studied by new techniques such as single photon emission computerised tomography(SPECT) and positron emission tomography( PET) which have in turn contributed significantly to our understanding of what happens during a stroke.

Stroke is the commonest cause of severe disability in the ageing population of any country. It produces much more devastating effects and the fortunate survivors, even if they suffer only limited impairment of the nervous system, rarely return to their jobs and social positions. Patients who survive a heart attack on the other hand normally return to their former jobs and social position. This has led to poor lobbying for stroke patients to safe-guard themselves and resulted in a nihilistic approach by doctors and the society. Recent understanding of the extraordinary capacities of the brain to compensate for damages suffered in a stroke should change this attitude. Though there is some specialisation or localisation of functions in the brain which are distributed over the larger area of the brain,there is a possibility of functional replacement. Other areas of the brain take over the responsibility of functions that have failed as a result of a stroke. All efforts should be made to rehabilitate the stroke survivors in their previous jobs and society. Doctors at the primary health care level should not feel reluctant to send stroke patients to specialised hospitals. There should be an ongoing continuous cooperative effort between neurologists and rehabilitation medicine. The rehabilitation medicine department should not only provide physiotherapy but all rehabilitative facilities which stroke victims require.

These include speech therapy and occupational therapy. Rehabilitation should start at the earliest possible moment because the opportunities lost at that early stage can never be recovered later on.

ANATOMY OF THE WONDERFUL BRAIN

The brain develops from a structure called the ectodermal neural tube in the foetus. By the end of the fourth week of gestation, the neural tube is completely formed and closed. After closure there is a narrow tail-like structure which develops into the spinal cord. The enlarged front part of the structure develops into the brain. It grows into the three primary divisions of the brain : the hind brain, mid brain and fore brain. With continued growth and development of the brain, individual structures get differentiated.

The adult brain consists of two cerebral hemispheres which are connected by the corpus callosum. The surface of the cerebral hemisphere resembles a walnut with its convoluted surface. Each hemisphere is divided into frontal, parietal, temporal and occipital lobes. On the surface, the lobes are subdivided further into areas on the basis of function, i.e. motor, sensory, speech, visual, hearing, etc. Immediately below the cortex is the corpus callosum. Below this are the basal ganglion, thalamus, hypothalamus (pituitary gland), mid brain, and pineal body. Below the mid brain are the pons, medulla oblongata and cerebellum. Like the cerebrum, the cerebellum has a cortex with folds. The cerebellum has two hemispheres united by a median vermis. Medulla oblongata continues as the spinal cord. The skull cavity which contains the brain, is divided into three fossae (depressions) by tough fibrous partitions into anterior middle and posterior (rear) cranial fossa. Cerebellum and the greater part of the brain stem occupy the posterior cranial fossa. Temporal lobe occupies the middle fossa. The greater part of the anterior fossa is occupied by two cerebral hemispheres. The vertebral column or the backbone encloses the spinal cord. The brain and the spinal cord are enveloped by a thin continuous membrane called the meninges. The outermost meningeal layer is called dura mater and is the toughest. It almost sticks to the skull bone. The entire brain and the spinal cord is bathed in a watery fluid called cerebrospinal fluid.

All body functions are represented in the brain, some in the left and some in the right hemisphere. For many years neuroanatomists, neurophyiologists and neuropsychologists talked about the dominance of a hemisphere or its specialisation and localisation. For example, language is represented in the left hemisphere. Musical appreciation and construction ability is represented in the right hemisphere. Recent observations on stroke patients, especially their ability to regain certain faculties lost after a stroke, however, cast doubt over such rigid localisation of the brain. Some experts believe that neurological functions are distributed over the entire brain even though some areas are more important than others. There is, therefore, a possibility of function replacement during rehabilitation after a stroke. The areas of the brain which usually remain dormant assume the responsibility for the functions when commonly recognised areas have failed to function because of a disease or a stroke.

It is very important for the readers to remember that right-sided functions like motor, sensory or visual fields have representation in the left hemisphere and left-sided functions are represented in the right hemisphere. The nerve fibers, both motor and sensory, carrying messages from and to the brain, cross at different levels in the central nervous system. The knowledge of the site where the fibres cross is important in localisation of the damaged area. Cerebellar cortex and its connections control the body functions on the same side, i.e. their action is ipsilateral. Similarly, cranial nerves which originate in the brain, have ipsilateral functional control. Some function like consciousness, sleep, etc. have bilateral representation. This functional knowledge is important in localisation of the damaged area of the brain at the bedside.

The heart is an important organ as it continuously pumps the oxygenated blood and perfuses all the tissues of the body through the network of arteries. The heart receives the purified or oxygenated blood from the lungs. The brain receives blood through two systems, called carotid, and vertebral-basilar system. As blood flowing through the carotid system does not normally mix with the vertebral-basilar blood, these two separate system were recognised a long time ago. From the heart the blood flows into the aorta. The aorta arch gives rise to three large arteries to supply the brain. They are the brachiocephalic artery, left common carotid artery, and left subclavian artery. The brachiocephalic artery further divides into the right common carotid and the right subclavian arteries. The right and left common carotid arteries divide into external and internal carotid arteries on either side of the neck. The internal carotid artery on entering the brain divided into two main branches : anterior cerebral artery and middle cerebral artery. Vertebral artery arises from the subclavian artery on each side and enters the cranial cavity through a large opening called the foramen magnum. Two vertebral arteries join together at the lower border of pons to form the basilar artery which at the upper border of pons and at the base of posterior cerebral arteries.

At the base of the brain, each anterior cerebral artery, right and left, are joined by a small communicating artery called the anterior communicating artery. Middle cerebral artery on each side joins the posterior cerebral artery through the communicating artery and is named as posterior communicating artery. This hexagonal arterial structure at the base of the brain joining the two carotid systems and vertebral basilar system via one anterior communicating and two posterior communicating arteries is named as the circle of Willis. Under normal circumstances the flow of blood remains on the same side, i.e. the right side of the brain is supplied by the right internal carotid artery and its branches and left side of the brain is supplied by the left internal carotid artery and its branches. The vertebral-basilar system supplies to the brain stem, cerebellum, occipital lobes and interior surface of the temporal lobes. About 300 to 400 ml of blood flows each minute into each carotid system and about 200 ml into the vertebral-basilar system. Most of the blood of the internal carotid artery passes through the middle cerebral artery.

As the arteries go deeper into the tissue, the side of these vessels becomes smaller and smaller. Small arteries are called arterioles. The pattern of arterial supply basically is the same for the entire brain. Small arteries and arterioles give off innumerable unnamed perforating branches that penetrate the substance of the brain. Most of the perforating vessels have very few interconnections. Blood flows from arterioles to capillaries for exchange of oxygen and other metabolic products. Deoxygenated blood with metabolic and products flows out in the veins. Venous blood through a network of veins and sinuses returns to the large veins in the neck from there it flows into the right side of the heart through superior vena cava. Blood from right side of the heart goes to the lungs for oxygenation.

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