stroke neuroimaging – some basics · stroke neuroimaging – some basics ... •to understand the...

Stroke neuroimaging –some basics

Dr Hedley EMSLEY PhD MRCP(UK)Consultant Neurologist &

Honorary Lecturer

Learning objectives

• To revise basic neuro‐anatomy

• To compare normal and abnormal scans with particular reference to stroke pathology

• To be able to relate the imaging report to the scan

• To understand the medical interpretation of scans and the implications for management

• To develop a level of knowledge to be able to understand current research in the area of language processing

Stroke – why do a brain scan?

• Stroke aetiology, natural history, investigation and management all differ by pathological type– 80% ischaemic– 15% intracerebral haemorrhage– 5% subarachnoid haemorrhage

• Is there haemorrhage?• Are there early signs of ischaemia?• Is there evidence of a stroke mimic (eg tumour)?• Is there salvageable tissue? • Is there an identifiable stenosis or occlusion?

Which type of scan?

• Computed axial tomography (CAT or CT)– Plain (unenhanced)– Contrast enhanced– CT angiography– CT perfusion

• Magnetic resonance imaging (MRI)– T1, T2, FLAIR– Diffusion weighted imaging (DWI)– Gradient echo– MR angiography (time of flight, contrast)

CT

• Cross sectional image formed from large series of X‐ray images taken around a single axis of rotation

• X‐rays blocked (or attenuated) to varying degree by different tissues

• Rapid and suitable for sick patient (eg acute stroke patient)

• Readily available 24 hours a day

• Gold standard for visualisation of haemorrhage

• Main concern is radiation exposure

right left

Acute CT. Early right MCAterritory ischaemia

CT perfusion. Reduced cerebral blood flow.

CT perfusion. Reduced cerebral blood volume.

MRI

• Excellent contrast between different soft tissues (including brain)

• No ionising radiation• Powerful magnetic field aligns nuclear magnetisation of hydrogen atoms within body water (including brain)

• Radio frequency fields then used to alter the alignment of the magnetisation

• Cross sectional images then generated from resultant electromagnetic signals

• Contrast agents (eg gadolinium) enhance appearance of blood vessels, tumours, inflammation

Vascular territories

• Concept of anterior and posterior (vertebrobasilar) circulation

• Circle of Willis

• Anterior, middle and posterior cerebral artery territories

• Oxfordshire Community Stroke Project (OCSP) classification

• Total anterior circulation syndrome (TACS)– hemiplegia and homonymous hemianopiacontralateral to the lesion, and

– either aphasia or visuospatialdisturbance

– with or without sensory deficit contralateral to the lesion

• Partial anterior circulation syndrome (PACS)– one or more of unilateral motor or sensory deficit, aphasia or visuospatialdysfunction (combined or not with homonymous hemianopia)

– motor or sensory deficit may be less extensive than in lacunarsyndromes (eg hand alone)

OCSP classification

OCSP classification

• Lacunar syndrome (LACS)– no visual field defect– no new disturbance of higher cortical function

– pure motor hemiparesis

– pure sensory deficit– sensorimotor stroke– ataxic hemiparesis– At least 2 of 3 contiguous areas (face, arm, leg), limb in its entirety

• Posterior circulation syndrome (POCS)– any one of:– cranial nerve impairment

– unilateral or bilateral motor or sensory deficit

– disorder of conjugate eye movement

– cerebellar dysfunction– homonymous hemianopia

– cortical blindness

iwt

• Low density

• Wedge shaped

• Grey & white matter

• Within known arterial vascular territory

• Proportionally little mass effect

Recognising an infarct

Early signs of ischaemia

• Hyperdense artery signs eg MCA

• Loss of insular ribbon

• Loss of grey/white matter differentiation in relation to caudate, lentiform nucleus, internal capsule

• Hypodense caudate or lentiform nuclei

Acute CT. Early right MCAterritory ischaemia

Repeat CT 1 day later. Malignant MCA infarction led to hemicraniectomy.

DW MRI at 5 days. Restricted diffusion pattern right hemisphere.

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Day 1

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Day 2

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Day 4

Summary

• Role of imaging

• Types of imaging

• Vascular territories

• OCSP classification

• Recognition of infarct / early ischaemia

• Example scans

stroke neuroimaging – some basics · stroke neuroimaging – some basics ... •to understand the...

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