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  1. J M Wardlaw
  1. Dr JM Wardlaw, Department of Clinical Neurosciences, Bramwell Dott Building, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK jmw{at}

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Stroke is a clinical syndrome.1 In the investigation of stroke and transient ischaemic attack (TIA) imaging is used to differentiate:

vascular from non-vascular lesions, such as tumours or infections
ischaemic from haemorrhagic stroke
arterial from venous infarction
and to distinguish anterior and posterior circulation strokes to determine whether a tight carotid stenosis is symptomatic or not.

In the future imaging may be used to show the extent of salvageable tissue in acute stroke before treatment. Imaging should be used to direct management. Investigation should be organised to resolve specific, preferably articulated, management dilemmas. This may include imaging to clarify and guide prognosis.

Computed tomography

Computed tomography (CT) will differentiate infarct from haemorrhage up to at least five days after stroke. Recent haemorrhages are high density (white) and usually rounded and space occupying. Infarcts are usually low density (dark) and occupying a vascular territory with some swelling (fig 1). In a patient with a stroke a normal scan excludes a haemorrhage and, in the absence of an alternative, infarction is assumed.2

Figure 1

 CT brain scan showing a right hemisphere total anterior circulation infarct (A) at four hours, and (B) at five days after symptom onset. Note on (A) the subtle signs of early infarction: loss of the basal ganglia on the right (white arrow—compare with the left where the caudate and lentiform nuclei are clearly visible), loss of the grey/white matter cortical differentiation (black arrowheads), a little swelling with sulcal effacement (black arrow and compare left side). On day 5 there is obvious hypodensity and massive infarct swelling with midline shift and obstruction of the left lateral ventricle.

Intravenous contrast is not normally required and may cause confusion.

There is some uncertainty as to how quickly small haemorrhages lose their characteristic whiteness and become isodense and then hypodense compared with normal brain, and so indistinguishable from an infarct. Certainly by 10 days, small haemorrhages will be indistinguishable from infarcts, and we have seen small haemorrhages disappear by seven days. Large haemorrhages remain visible as such for 2–3 weeks. …

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