A transient ischaemic attack is defined as stroke symptoms and signs that resolve within 24 hours [1].
Sometimes known as minor stroke,
in which blood supply to the brain is temporarily disturbed leading to stroke like symptoms,
but where these symptoms resolve within 24 hours.
The cause of TIA is the same as the cause of an ischaemic stroke.
TIAs carry a significant mortality and morbidity risk.
They may be the only warning that a major stroke is imminent [2].
There is a 20 percent risk of full stroke within the first four weeks after TIA [3].
Around 150,000 people per year have a suspected TIA or minor stroke [4].
However,
only 35 percent are seen and investigated in a neurovascular clinic within seven days [3].
Investigating and treating high-risk patients with TIA within 24 hours could reduce by 80 percent the number of people who go on to have a full stroke [5].
The risk of stoke is greatest immediately after a new TIA.
ABCD2 scoring system (table 1) determines the likely risk of subsequent stroke.
Table 1: ABCD2 score
•Age ≥ 60? +1
•BP ≥ 140/90 mmHg at initial evaluation? +1
•Clinical Features of the TIA:
Unilateral Weakness? +2
Speech Disturbance without Weakness? +1
•Duration of Symptoms:
10-59 minutes? +1
≥ 60 minutes? +2
•Diabetes Mellitus? +1
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People who have had a suspected TIA who are at high risk of stroke (ABCD2≥4/ crescendo TIA) in whom the vascular territory or pathology is uncertain should undergo urgent brain imaging within 24 hours whereas people who have had a suspected TIA who are at lower risk of stroke (ABCD2<4) in whom the vascular territory or pathology is uncertain should undergo brain imaging within 7 days at the most [1,2].
Approximately 50 percent of suspected TIAs require magnetic resonance imaging (MRI) of the brain [2].
MRI in TIA needs to include diffusion-weighted imaging (DWI,
which shows lesions in up to half of TIAs) and gradient-echo sequences (GRE,
which is very sensitive to bleeding).
Magnetic resonance angiography (MRA) will also be appropriate to clarify the arteries affected in many instances.
Computed tomography (CT) has low spatial resolution and may be unable to detect small lesions.
It may,
however,
remain an appropriate alternative in those for whom MRI is contraindicated.
About 80 percent of TIAs require imaging of the carotid arteries.
The remaining 20 percent of people have a vertebrobasillar TIA (brainstem/ cerebellum) and will not benefit from carotid imaging [2].
Carotid imaging requires assessment of severity of stenosis at the carotid bifurcation and exclusion of an embolic source in the carotid arteries or elsewhere.
Duplex ultrasound is the most widely available and frequently used initial investigation for assessment of carotid stenosis.
However,
duplex ultrasound is operator dependent requiring significant skill in image and data acquisition as well as interpretation.
Evidence suggests that more recently introduced non-invasive imaging modalities,
especially contrast enhanced magnetic resonance angiography (CEMRA) may be more accurate [6].
Exclusion of other sources of emboli will require overview imaging techniques that can image from the origin of the carotid artery to the circle of Willis within the brain including CEMRA and CT angiography (CTA).
In rare cases,
clots can be formed within the heart for which echocardiography may be required.
Carotid imaging can identify those people with significant carotid stenosis who would benefit from carotid intervention (carotid endartrectomy/ stenting) in order to prevent stroke.
Significant disease is usually defined as symptomatic carotid stenosis of 50-99% using criteria from North America Symptomatic Endartrectomy Trial (NASCET) [7,8] or 70-99% using criteria from European Carotid Surgery Trialists’ (ECST) Collaborative Group [9].
A NASCET stenosis value of 50% is broadly equivalent to a 70% value in ECST [10]. Table 2 demonstrates urgency of brain imaging,
carotid imaging/intervention based on the predicted risk of stroke.
Table 2: Urgency of brain imaging,
carotid imaging/intervention in suspected TIA
High risk of stroke (ABCD2≥4/crescendo TIA)
- Brain imaging (MRI/MRA,
CT/CTA if MRI is contraindicated): within 24 hours
- Carotid imaging (duplex scan,
CEMRA,
CTA): within 24 hours
- Carotid intervention (NASCET 50-99%,
ECST 70-99%): within 48 hours
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Low risk of stroke (ABCD2<4)
- Brain imaging (MRI/MRA,
CT/CTA if MRI is contraindicated): within 7 days at the most
- Carotid imaging (duplex scan,
CEMRA,
CTA): within 7 days at the most
- Carotid intervention (NASCET 50-99%,
ECST 70-99%): within 14 days
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✱ symptomatic carotid stenosis of <50% using NASCET criteria,
or <70% using ECST criteria are managed medically and no surgical intervention is indicated.
The aim of this audit is to compare our local practice in imaging TIAs with nationally agreed guidelines [1,2].