Page 300 - Medicine and Surgery

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296 Chapter 7: Nervous system

Age Other features of an MCA territory infarct include
Uncommon under 40 years. an ipsilateral UMN lesion of the face (weakness of
the lower facial muscles), hemianopic visual field
Sex loss and if the dominant hemisphere is affected
M > F, but mortality twice as high in females. dysphasia may occur due to infarction of areas gov-
erning speech (Wernicke’s and Broca’s areas).
Geography Posterior circulation (the vertebral, basilar arteries and
Black community, Japanese more common. their branches) strokes affect the brainstem, cerebel-
lum and occipital lobes. One characteristic but uncom-
Aetiology mon pattern is lateral medullary syndrome which can
20% of strokes are haemorrhagic and 80% are ischaemic, be caused by thromboembolism of the posterior inferior
of which two-thirds arise from extracranial lesions and cerebellar artery (PICA) or the vertebral artery. It causes
one-third arise from intracranial lesions. Strokes may sudden vertigo and vomiting. On examination there is
also be due to subarachnoid haemorrhage. Risk factors ipsilateral ataxia (loss of co-ordination), contralateral
for stroke can be divided into loss of pain and temperature sensation and there may
Intra- or extra-cranial atherosclerosis: In particular be nystagmus, diplopia and an ipsilateral Horner’s syn-

hypertension, smoking, hyperlipidaemia, family his- drome.
tory of stroke or ischaemic heart disease and diabetes If the pontine reticular formation is involved in brain-
mellitus. stem infarcts, important basic functions such as alert-
Heart disease: Valvular heart disease such as mitral ness,breathingandcirculationmaybeaffectedleading

stenosis, infective endocarditis, and any condition to coma and death.
which predisposes to mural thrombus such as atrial Lacunar infarcts are small (<1 cm) often slit-shaped
fibrillation or myocardial infarction. areas of infarction usually in the basal ganglia, inter-
Less common causes: Hyperviscosity or prothrom-
nal capsule and pons caused by hyaline arteriosclerosis
boticstates,e.g.polycythaemia,oralcontraceptivepill; within the small fine perforating arteries of the brain.
vasculitis; clotting disorders. They are predisposed to by hypertension and diabetes,
are often asymptomatic but may cause focal neurologi-
Pathophysiology cal defects such as weakness of a single limb, or limited
Haemorrhagic strokes are discussed elsewhere. Ischa- ataxia.
emic strokes are due to the interruption of arterial blood Multiplelacunarorlargerinfarctscanresultinamulti-
supply, and the clinical picture depends on the size of infarct dementia with a picture of loss of intellect oc-
artery and hence extent of territory affected, the area curring in a step-wise pattern. The final picture may
affected, and whether there is temporary or permanent include dementia and a shuffling gait which resembles
ischaemia and hence infarction. Parkinson’s Disease.
In clinical situations a full neurological examination
Clinical features should be performed and a careful cardiovascular ex-
Anterior circulation (carotid territory) strokes are the amination in order to reveal any source of embolus or
most common, in particular those involving a branch of other predisposing disease.
the middle cerebral artery. This causes infarction of the
motor pathways (at the level of the motor cortex or the Macroscopy/microscopy
internal capsule) and usually results in a contralateral In the first 24 hours, there is little macroscopic change.
hemiparesis. This is an upper motor neurone (UMN) The tissue may look paler and lose differentiation be-
deficit, i.e. increased tone, reduced power and brisk ten- tween white and grey matter.
don reflexes, although acutely there may be a flaccid, The normal pattern of tissue change within the
areflexic paralysis. The arm tends to be affected more brain following a stroke is liquifactive necrosis. Struc-
than the leg (the motor cortex for the leg is supplied by tural breakdown takes place, the infarcted tissue be-
the anterior cerebral artery). comes soft and is at risk of reperfusion haemorrhage.