Sunday 22 January 2012
STROKE
A stroke , also known as a cerebrovascular accident (CVA ), is the rapid loss of brain function(s) due to disturbance in the blood supply to the brain. This can be due to ischemia (lack of blood flow) caused by
blockage (thrombosis, arterial embolism), or a hemorrhage (leakage of blood). [1] As a result, the affected area of the
brain cannot function, which
might result in an inability to move one or more limbs on
one side of the body , inability to understand or formulate speech, or an inability to see one side of the visual field .[2] A stroke is a medical emergency and can cause permanent neurological damage, complications, and
death. It is the leading cause
of adult disability in the United States and Europe and the second leading cause of death worldwide. [3]Risk factors for stroke include old age, hypertension (high blood pressure), previous stroke or transient ischemic attack (TIA), diabetes, high cholesterol, cigarette smoking and atrial fibrillation .[2] High blood pressure is the most
important modifiable risk factor of stroke. [2] A silent stroke is a stroke that does not have any outward
symptoms, and the patients
are typically unaware they
have suffered a stroke.
Despite not causing
identifiable symptoms, a silent stroke still causes damage to
the brain, and places the
patient at increased risk for
both transient ischemic attack and major stroke in the
future. Conversely, those who
have suffered a major stroke
are at risk of having silent strokes. [4] In a broad study in 1998, more than 11 million
people were estimated to
have experienced a stroke in
the United States.
Approximately 770,000 of
these strokes were symptomatic and 11 million
were first-ever silent MRI
infarcts or hemorrhages. Silent strokes typically cause lesions which are detected via the use
of neuroimaging such as MRI. Silent strokes are estimated to
occur at five times the rate of symptomatic strokes. [5][6] The risk of silent stroke
increases with age, but may
also affect younger adults and
children, especially those with acute anemia.[5][7] An ischemic stroke is
occasionally treated in a
hospital with thrombolysis (also known as a "clot
buster"), and some
hemorrhagic strokes benefit
from neurosurgery. Treatment to recover any lost
function is termed stroke rehabilitation, ideally in a stroke unit and involving health professions such as speech and language therapy, physical therapy and occupational therapy . Prevention of recurrence may
involve the administration of antiplatelet drugs such as aspirin and dipyridamole , control and reduction of hypertension , and the use of statins. Selected patients may benefit from carotid endarterectomy and the use of anticoagulants.[2] Classification A slice of brain from the autopsy of a person who suffered an acute middle cerebral artery (MCA) stroke Strokes can be classified into
two major categories: ischemic and hemorrhagic.[8] Ischemic strokes are those
that are caused by
interruption of the blood
supply, while hemorrhagic
strokes are the ones which
result from rupture of a blood vessel or an abnormal vascular structure. About 87% of
strokes are caused by
ischemia, and the remainder
by hemorrhage. Some
hemorrhages develop inside
areas of ischemia ("hemorrhagic
transformation"). It is
unknown how many
hemorrhages actually start as ischemic stroke. [2] Ischemic Main articles: Cerebral infarction and Brain ischemia In an ischemic stroke, blood
supply to part of the brain is
decreased, leading to
dysfunction of the brain tissue
in that area. There are four
reasons why this might happen: 1. Thrombosis (obstruction of
a blood vessel by a blood
clot forming locally) 2. Embolism (obstruction due
to an embolus from
elsewhere in the body, see below), [2] 3. Systemic hypoperfusion
(general decrease in blood supply, e.g., in shock)[9] 4. Venous thrombosis.[10] Stroke without an obvious
explanation is termed
"cryptogenic" (of unknown
origin); this constitutes 30-40% of all ischemic strokes. [2][11] There are various classification
systems for acute ischemic
stroke. The Oxford
Community Stroke Project
classification (OCSP, also
known as the Bamford or Oxford classification) relies
primarily on the initial
symptoms; based on the
extent of the symptoms, the
stroke episode is classified as total anterior circulation
infarct (TACI), partial anterior circulation infarct (PACI), lacunar infarct (LACI) or posterior circulation infarct (POCI). These four entities
predict the extent of the
stroke, the area of the brain
affected, the underlying cause, and the prognosis.[12][13] The TOAST (Trial of Org 10172 in Acute Stroke Treatment)
classification is based on
clinical symptoms as well as
results of further
investigations; on this basis, a
stroke is classified as being due to (1) thrombosis or
embolism due to atherosclerosis of a large artery, (2) embolism of cardiac origin, (3) occlusion of a small
blood vessel, (4) other
determined cause, (5)
undetermined cause (two
possible causes, no cause
identified, or incomplete investigation). [2][14] Hemorrhagic Main articles: Intracranial hemorrhage and intracerebral hemorrhage An intraparenchymal bleed (bottom arrow) with surrounding edema (top arrow) Intracranial hemorrhage is the
accumulation of blood
anywhere within the skull
vault. A distinction is made
between intra-axial hemorrhage (blood inside the brain) and extra-axial hemorrhage (blood inside the skull but outside the brain).
Intra-axial hemorrhage is due
to intraparenchymal hemorrhage or intraventricular hemorrhage (blood in the ventricular
system). The main types of
extra-axial hemorrhage are epidural hematoma (bleeding between the dura mater and the skull, subdural hematoma (in the subdural space) and subarachnoid hemorrhage (between the arachnoid mater and pia mater). Most of the hemorrhagic stroke
syndromes have specific
symptoms (e.g., headache, previous head injury). Signs and symptoms Stroke symptoms typically
start suddenly, over seconds
to minutes, and in most cases
do not progress further. The
symptoms depend on the area
of the brain affected. The more extensive the area of
brain affected, the more
functions that are likely to be
lost. Some forms of stroke can
cause additional symptoms.
For example, in intracranial hemorrhage, the affected area
may compress other
structures. Most forms of
stroke are not associated with headache, apart from subarachnoid hemorrhage and
cerebral venous thrombosis
and occasionally intracerebral
hemorrhage. Early recognition Various systems have been
proposed to increase
recognition of stroke by
patients, relatives and
emergency first responders. A systematic review , updating a previous systematic review
from 1994, looked at a
number of trials to evaluate
how well different physical examination findings are able to predict the presence or
absence of stroke. It was
found that sudden-onset face
weakness, arm drift (i.e., if a
person, when asked to raise
both arms, involuntarily lets one arm drift downward) and
abnormal speech are the
findings most likely to lead to
the correct identification of a
case of stroke (+ likelihood ratio of 5.5 when at least one of these is present). Similarly,
when all three of these are
absent, the likelihood of
stroke is significantly
decreased (– likelihood ratio of 0.39).[15] While these findings are not perfect for
diagnosing stroke, the fact
that they can be evaluated
relatively rapidly and easily
make them very valuable in
the acute setting. Proposed systems include FAST (stroke) (face, arm, speech, and time),[16] as advocated by the Department of Health (United Kingdom) and The Stroke Association , the American Stroke
Association
(www.strokeassociation.org) ,
National Stroke Association
(US www.stroke.org), the Los
Angeles Prehospital Stroke Screen (LAPSS) [17] and the Cincinnati Prehospital Stroke Scale (CPSS).[18] Use of these scales is recommended by professional guidelines.[19] For people referred to the emergency room , early recognition of stroke is
deemed important as this can
expedite diagnostic tests and
treatments. A scoring system
called ROSIER (recognition of
stroke in the emergency room) is recommended for
this purpose; it is based on
features from the medical
history and physical examination. [19][20] Subtypes If the area of the brain
affected contains one of the
three prominent central nervous system pathways — the spinothalamic tract, corticospinal tract, and dorsal column (medial lemniscus), symptoms may include: hemiplegia and muscle weakness of the face numbness reduction in sensory or
vibratory sensation initial flaccidity
(hypotonicity), replaced by
spasticity (hypertonicity),
hyperreflexia, and obligatory synergies. [21] In most cases, the symptoms
affect only one side of the
body ( unilateral). Depending on the part of the brain
affected, the defect in the
brain is usually on the
opposite side of the body.
However, since these
pathways also travel in the spinal cord and any lesion there can also produce these
symptoms, the presence of
any one of these symptoms
does not necessarily indicate a
stroke. In addition to the above CNS
pathways, the brainstem give rise to most of the twelve cranial nerves . A stroke affecting the brain stem and
brain therefore can produce
symptoms relating to deficits
in these cranial nerves: altered smell, taste, hearing,
or vision (total or partial) drooping of eyelid ( ptosis) and weakness of ocular muscles decreased reflexes: gag,
swallow, pupil reactivity
to light decreased sensation and
muscle weakness of the
face balance problems and nystagmus altered breathing and heart
rate weakness in sternocleidomastoid muscle with inability to turn head
to one side weakness in tongue
(inability to protrude and/
or move from side to side) If the cerebral cortex is involved, the CNS pathways
can again be affected, but also
can produce the following
symptoms: aphasia (difficulty with verbal expression, auditory
comprehension, reading
and/or writing Broca's or Wernicke's area typically involved) dysarthria (motor speech disorder resulting from
neurological injury) apraxia (altered voluntary movements) visual field defect memory deficits
(involvement of temporal lobe) hemineglect (involvement of parietal lobe) disorganized thinking,
confusion, hypersexual gestures (with
involvement of frontal
lobe) anosognosia (persistent
denial of the existence of a,
usually stroke-related,
deficit) If the cerebellum is involved, the patient may have the
following: trouble walking altered movement
coordination vertigo and or disequilibrium Associated symptoms Loss of consciousness, headache, and vomiting
usually occurs more often in
hemorrhagic stroke than in
thrombosis because of the
increased intracranial pressure
from the leaking blood compressing the brain. If symptoms are maximal at
onset, the cause is more likely
to be a subarachnoid
hemorrhage or an embolic
stroke.
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