Brain Imaging (CT/MRI) in Stroke & Haemorrhage — MRCP Part 1
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Brain Imaging (CT/MRI) in Stroke & Haemorrhage — MRCP Part 1

TL;DR

In acute stroke, non-contrast CT is the first-line test to rapidly exclude intracranial haemorrhage, while MRI (especially DWI) is more sensitive for early ischaemia and posterior circulation strokes. For MRCP Part 1, questions focus on choosing the correct modality, recognising time-dependent imaging changes, and avoiding classic interpretation traps.


Why this matters for MRCP Part 1

Brain imaging is a consistently tested area because it underpins emergency decision-making and differentiates ischaemic stroke from haemorrhage. Examination stems commonly assess:

  • Which scan to request first

  • What a “normal” scan does and does not exclude

  • How appearances change with time

  • How imaging findings alter management (e.g. thrombolysis eligibility)

A strong grasp of core principles is sufficient; advanced neuroradiology detail is not required.


Scope: what you are expected to know

For MRCP Part 1, candidates should be able to:

  • Select CT vs MRI appropriately in acute neurological presentations.

  • Recognise typical imaging appearances of ischaemic stroke and intracranial haemorrhage.

  • Understand timing-related changes on CT and MRI.

  • Identify scenarios where imaging may appear normal despite pathology.

Core high-yield points (exam-focused)

1) Non-contrast CT is first-line in suspected acute stroke

  • Indication: Any suspected acute stroke.

  • Purpose: Rapid exclusion of intracranial haemorrhage.

  • Key exam rule: A normal CT does not exclude acute ischaemic stroke, particularly within the first 24 hours.

2) Early CT signs of ischaemic stroke

CT may be normal initially, but early features include:

  • Loss of grey–white matter differentiation

  • Insular ribbon sign (middle cerebral artery territory)

  • Sulcal effacementThese may appear within 3–6 hours, but absence does not rule out infarction.

3) CT appearance of haemorrhage over time

  • Acute haemorrhage: Hyperdense (bright white)

  • Subacute haemorrhage: Isodense

  • Chronic haemorrhage: HypodenseDensity change with time is a common MRCP Part 1 testing point.

4) MRI diffusion-weighted imaging (DWI)

  • Most sensitive modality for detecting acute ischaemic stroke.

  • Can show infarction within minutes of onset.

  • Particularly useful for:

    • Posterior circulation strokes

    • Brainstem and cerebellar infarcts

5) MRI FLAIR and stroke timing

  • DWI-positive but FLAIR-negative lesions suggest hyperacute stroke (<4.5 hours).

  • This concept is frequently referenced in exam explanations.

6) CT vs MRI: comparison table

Feature

CT Brain

MRI Brain

Speed

Very fast

Slower

Availability

Widely available

Limited acutely

Best for

Excluding haemorrhage

Early ischaemia

Posterior fossa

Poor

Excellent

Early stroke sensitivity

Low

High (DWI)

7) Typical haemorrhage locations

  • Hypertensive haemorrhage: Basal ganglia, thalamus, pons, cerebellum

  • Lobar haemorrhage: Suggests cerebral amyloid angiopathy

  • Subarachnoid haemorrhage: Blood in sulci and basal cisterns (CT most sensitive in first 24 hours)

8) When CT can miss pathology

  • Hyperacute ischaemic stroke

  • Small lacunar infarcts

  • Posterior circulation strokesMRI is often mentioned in exam stems to highlight these limitations.

MRCP Part 1 candidate revising CT and MRI brain imaging for stroke and haemorrhage

Mini-case (single best answer)

Case: A 70-year-old woman presents 2 hours after sudden onset left-sided weakness and facial droop. Non-contrast CT brain is normal.

Question: What is the correct interpretation of this scan?

Answer: The CT excludes intracranial haemorrhage but does not exclude acute ischaemic stroke.

Explanation: Early ischaemic changes may not be visible on CT. In MRCP Part 1 questions, thrombolysis decisions hinge on clinical presentation plus exclusion of haemorrhage, not visual confirmation of infarction.


Most tested subtopics to memorise

  1. CT first in acute stroke

  2. Hyperdense blood = acute haemorrhage

  3. Normal CT ≠ no stroke

  4. MRI DWI detects infarction earliest

  5. Posterior circulation strokes may be CT-negative early


Common pitfalls (exam traps)

  • Assuming a normal CT rules out stroke

  • Forgetting that haemorrhage density changes with time

  • Choosing MRI as first-line in an unstable patient

  • Missing subarachnoid haemorrhage due to delayed imaging

  • Confusing lacunar infarcts with haemorrhage locations


Practical study-tip checklist

  • Always ask: “What is the first investigation?”

  • Link time since symptom onset with expected imaging findings.

  • Memorise classic haemorrhage locations and associations.

  • Use tables to reinforce CT vs MRI differences.

  • Practise imaging-heavy questions regularly.


FAQs

Is CT or MRI better for acute stroke in exams?

CT is first-line to exclude haemorrhage; MRI is more sensitive for early infarction. Exams test correct sequencing rather than absolute accuracy.

Can CT miss an acute ischaemic stroke?

Yes. CT may be normal in the first 24 hours, especially in early or posterior circulation strokes.

What does acute intracerebral haemorrhage look like on CT?

It appears hyperdense (bright white) due to fresh blood.

Why is MRI DWI important in stroke?

DWI detects restricted diffusion within minutes of infarction, making it the most sensitive technique for early ischaemic stroke.


Ready to start?

Test and reinforce your brain imaging knowledge with exam-standard practice:

Sources

 
 
 
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