Ischemic stroke (summary)

• this is a basic article for medical students and non-radiologists
• for more information, see the main stroke article

Stroke is a clinical diagnosis where an acute neurological deficit follows a cerebrovascular insult.

There are two main groups of stroke: ischaemic (>80%) or haemorrhagic (<20%).

Epidemiology

Stroke is an extremely common condition - it is the leading cause of disability and the second cause of morbidity.

Vascular risk factors are shared in ischaemic stroke (age, male gender, family history, hypertension, smoking, hyperlipidaemia, diabetes).  Hypertension is also a primary risk factor in haemorrhagic strokes.

Clinical presentation

Stroke is characterised as a sudden neurological deficit.  The symptoms that manifest depend on the vascular territories involved.  In any patients with acute neurological changes (motor, sensory, speech, vision, consciousness, behaviour) a stroke should be considered.

Time of onset is important when considering treatment options.  Symptoms can fluctuate depending on the underlying pathology and collateral supply to affect areas.

Pathology

The effects of a stroke come from the brain parenchyma being deprived of blood flow, with cell death resulting from the loss of oxygen and nutrients it delivers.

In ischaemic strokes, cerebral arteries can become occluded by a thrombus or embolus.  This affects the brain parenchyma supplied by the vessel with neurological deficit from the affected systems.

In some cases this is a temporary loss, resulting in a transient ischaemic attack (TIA), but these should be managed as strokes in the emergent situation.

As cell death takes place, there is oedema and swelling of surrounding tissues which resolves over time as gliosis.

Radiographic features

Imaging is critical in diagnosis and management of stroke.  It is part of treatment guidelines and relies on clear communication between clinical and radiology teams.

CT

Non-contrast CT is the first line imaging investigation in investigation of stroke.

The range of appearances in ischaemic stroke is well described in the full article.

In the emergency setting, CT can be used to exclude a haemorrhagic stroke (figure 2) - these would appear hyperdense, either in vessel rich areas such as the basal ganglia, or in the lobes.  If present it would exclude thrombolysis as a treatment option.

An important early sign in ischaemic stroke is the hyperdense vessel sign (figure 4.1).  This can be evidence of blood products (thrombus/embolus) in the vessel but disappears in the first few hours.

Other early signs include loss of grey/white differentiation - a "blurring" at the edges of ischaemic areas (fig 1.1).  As infarction develops, the affected territories appear hypodense with swelling and oedema of surrounding tissues (fig 1.2).

Later appearances following gliosis - the liquifying necrosis that occurs in cell death - leave a large low density area (fig 1.4).

CTA

Angiography has a growing role in CT imaging and has a number of roles.  It can identify thrombi in vessels guiding thrombolysis clot retrieval.  It can also reveal other causative factors for stroke (dissection, atherosclerosis, aneurysms).

MRI

MRI is a fantastic tool for investigating stroke but is time-consuming and not widely available.

It can contrast between haemorrhagic and ischaemic infarcts.  Analysis of different sequences (particularly DWI and ADC) can be used to determine chronicity of strokes.

Ultrasound

Carotid doppler ultrasound is used in the follow-up of most patients.  After acute investigations and management has been started, patients may be for consideration of carotid endarterectomy if there is stenosis in relevant arteries.

Treatment and prognosis

In the immediate situation, many stroke patients are for consideration of thrombolysis.  This "clot-buster" medication is only for use in ischaemic strokes less than 4.5 hours old (consult local protocol) and if patients meet particular criteria.  All thrombolysis "candidates" should be discussed with the on-call stroke service.

All cases should be managed in specialist stroke centres as good rehabilitation is important.  

In ischaemic stroke, treatment is with anti-platelets and reduction of risk factors through medication (blood pressure, cholesterol) and lifestyle choices.

In haemorrhagic stroke, blood pressure control is the mainstay.

Differential diagnosis

The important distinction to make in the immediate stage is between ischaemic and haemorrhagic strokes.

Other mimics include space-occupying lesions (which can also lead to strokes), extra-axial bleeds, epilepsy (Todd's paresis), migraines...  This long (and not exhausted) list is why a good clinical history, examination and appropriate timely imaging is so important.