Ischaemic stroke (summary)

• this is a basic article for medical students and non-radiologists

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%)¹.

Epidemiology

Stroke is an extremely common condition and it is the leading cause of disability and the third highest cause of mortalitiy in the UK ^1,22,3.

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 results in scarring (gliosis).

Radiographic features

Imaging is critical in diagnosis and management of stroke. Treatment guidelines rely on imaging findings and the clear communication between clinical and radiology teams.

CT

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

In the emergency setting, CT is used to exclude haemorrhage (case 2) which appears as hyperdense regions, usually in vessel rich areas such as the basal ganglia. Haemorrhage excludes thrombolysis as a treatment option.

An important early sign in ischaemic stroke is the hyperdense vessel sign (case 4). This is the result of thrombus/embolus in the vessel and is associated with increased complications when thrombolysis is used.

Other early signs include loss of grey-white differentiation with "blurring" at the edges of ischaemic areas (case 1, first CT). As infarction develops, the affected territories appear hypodense with swelling and oedema of surrounding tissues (case 1, second CT).

Later appearances liquifying necrosis occurs following cell death to leave large areas of low density corresponding to encephalomalacia, with surrounding scarring corresponding to gliosis (case 1, fourth CT). 

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 in the acute setting.

It can contrast between haemorrhagic and ischaemic infarcts, assess parenchymal damage, determine the age of stroke (diffusion imaging) and assess perfusion of the affected region.

Ultrasound

Carotid doppler ultrasound is used to assess the carotid arteries in patients who have had a stroke. 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 many institutions, many stroke patients are considered for thrombolytic therapy. This "clot-buster" medication is only for use in ischaemic strokes that are less than 4.5 hours old (consult local protocol) and if patients meet particular criteria ^3,44,5. All thrombolysis "candidates" should be discussed with the on-call stroke service and CT performed to exclude haemorrhage.

There is growing evidence that "clot retrieval" (as occurs in coronary angiograms from STEMIs) results in improved function and earlier discharges ⁵⁶. 

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), and migraines. This long (and not exhaustive) list is why a good clinical history, examination and appropriate timely imaging is so important.

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