1. CONFIRM THE DIAGNOSIS
Computerised tomography (CT scan) Ideally, all patients should have a CT scan. In practice, a CT scan is performed if:
- there is doubt about the diagnosis
- symptoms progress
- conscious level is depressed
- if thrombolytic or anticoagulant treatment is considered or aspirin commenced or continued
- neck stiffness is present or prior to any invasive investigation.
Phaemorrhage or tumour Pcerebral haemorrhage (see page 259)
(note hyperdense thrombosed middle cerebral artery)
Infarction is evident as a low-density lesion which conforms to a vascular territory, i.e. usually wedge shaped. It is not immediately visible on CT but in most patients becomes apparent in 4—7 days. CT scan also identifies:
- the site and size of the infarct, providing a prognostic guide
- the presence of haemorrhagic infarction where bleeding occurs into the infarcted area
- intracerebral haemorrhage or tumour.
Magnetic resonance imaging (MRI)
T1 prolongation (i.e. hypointensity in relation to white and grey matter) occurs within a few hours of onset of ischaemic symptoms. Intracranial vessel occlusions show an absence of a 'signal void'. Posterior circulation strokes (lacunes) are more readily identified than with CT.
2. DEMONSTRATE THE SITE OF PRIMARY LESION
(a) Non-invasive investigation
Ultrasound - Dopplcr/Duplex scanning: assesses extra- and intracranial vessels (page 42). A normal study precludes the need for angiography.
Cardiac ultrasound (transthoracic or transoesophageal): this often reveals a cardiac embolic source in young people with stroke, e.g. prolapsed mitral valve, patent foramen ovale. Magnetic resonance angiography (MR A) Using 'time of flight' techniques, a non-invasive image of extra and intracranial vasculature is obtained. MRA overestimates the degree of stenosis and is insensitive to ulcerative plaque detection.
(b) Invasive investigation
The combination of the above techniques has decreased the need for invasive investigation but often cerebral angiography is still required to make a definitive diagnosis. The role and safety of angiography immediately following infarction is uncertain. In the elderly or poor-risk patient, investigations to demonstrate the site of the primary lesion may be inappropriate.
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