Urgent non-contrast CT head in suspected stroke
In suspected acute stroke, an urgent non-contrast CT head (a plain scan without contrast dye) is the first scan, because it shows whether the brain is bleeding.
Remember
In a suspected acute stroke, scan before you treat: the urgent CT head shows or excludes bleeding, and that decides which treatment can start.
Memory aid
bleed or block? Scan before you treat.
Ask first whether the cause is a bleed or a blockage, and scan before you give treatment.
A sudden focal deficit (a problem in one region, for example weakness of one side) in suspected acute stroke could be due to a bleed or a blockage. An ischaemic stroke (caused by a blocked artery) and a haemorrhagic stroke (caused by bleeding) can look the same from the symptoms alone, so only imaging can tell them apart.
The two types need opposite treatments. An ischaemic stroke may be treated with thrombolysis (a drug that dissolves the clot) or by mechanical removal of the clot, and those treatments could be dangerous if the brain is bleeding. Treatment therefore cannot start until haemorrhage has been ruled out, and the success in restoring lost function is time-dependent.
That is the job of the urgent non-contrast CT head. It is fast and widely available, and it shows whether there is bleeding. If no bleeding is seen, the stroke is presumed likely to be ischaemic, and treatment for that can begin.
The scan has limits. In the first few hours of an ischaemic stroke it can look normal, so a normal result excludes bleeding but does not exclude ischaemia. An infarct (area of dead tissue) is usually not obvious until about 6 to 12 hours.
MRI shows ischaemia better, but it takes longer and is often less available, so it is not the first test, although it may follow. CT angiography, which uses a contrast dye to outline the arteries, can reveal a blocked vessel. In suitable patients, it is done alongside or after the plain CT, without delaying treatment.
Key facts
- First scan
- an urgent non-contrast CT head in suspected acute stroke.
- Purpose
- to rule out haemorrhage before thrombolysis or other reperfusion treatment (restoring blood flow to a blocked artery).
- Normal early scan
- it excludes haemorrhage but does not exclude an early ischaemic stroke.
- Scan times
- CT usually takes 10 to 20 minutes, while MRI usually takes from 15 minutes to an hour or longer.
- After the CT
- CT angiography and MRI follow where needed, and they do not replace the first CT.
Exam traps
- MRI shows early ischaemia better than CT, but it does not make a better first scan in suspected stroke, because it takes longer and is often less available.
- A normal early CT does not exclude ischaemic stroke, because in the first hours an infarct is frequently not seen.
- Typical stroke symptoms do not remove the need for a scan, because either a blocked artery or a bleed can cause them, and clot-dissolving treatment could cause harm if the brain is bleeding.
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