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Imaging in acute ischaemic stroke

Non-contrast CT excludes haemorrhage and looks for early signs (ASPECTS), CTA looks for large vessel occlusion, and perfusion or DWI–FLAIR mismatch selects patients beyond the time window — and the aim is never to delay treatment.

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Why it matters in the exam

The first test in suspected stroke is non-contrast head CT, and its main role is to exclude haemorrhage. Early infarct signs: a hyperdense MCA, loss of the insular ribbon, blurring of the lentiform nucleus and sulcal effacement. The ASPECTS score divides the MCA territory into 10 regions and subtracts a point for each region with early ischaemic change; 6 or more supports thrombectomy within 6 hours, and trials from 2023 showed benefit also with a large core (ASPECTS 3–5) in selected patients. CTA from the aortic arch to the vertex looks for large vessel occlusion (LVO) — it is done at once and creatinine is not awaited.

In the 6–24 hour window patients are selected for thrombectomy by a mismatch between core size and clinical severity or penumbra — CT perfusion or MRI (based on the DAWN and DEFUSE 3 trials). With unknown onset (waking up with stroke): positive DWI with still-negative FLAIR suggests an infarct younger than 4.5 hours and allows thrombolysis. On MRI: DWI bright and ADC dark within minutes; FLAIR becomes positive after several hours; ADC returns to "normal" (pseudonormalisation) after about a week to 10 days; gyral enhancement appears in the subacute stage. On CT, after 2–3 weeks the infarct may again look almost normal (fogging).

The infarct pattern points to the mechanism: infarcts in several arterial territories — a cardioembolic source; infarcts in border zones between territories (watershed) — hypoperfusion, for example hypotension or severe carotid stenosis; lacunes in the deep nuclei — small vessel disease. Cervical artery dissection in a young patient with neck pain and Horner syndrome: a crescent-shaped intramural haematoma bright on fat-suppressed T1, a "string-like" narrowing or a tapering occlusion. Stroke in a child: think of arteriopathy, moyamoya and sickle cell anaemia.

Key points

• Non-contrast CT first — to exclude haemorrhage.
• ASPECTS 6 or more — thrombectomy within 6 hours.
• CTA for LVO, and perfusion at 6–24 hours.
• DWI positive and FLAIR negative — less than 4.5 hours.
• Several territories — embolism; border zones — hypoperfusion.

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Sources

• AHA/ASA Guidelines for the Early Management of Patients With Acute Ischemic Stroke, 2019 update — Imaging
• European Stroke Organisation Guidelines on Mechanical Thrombectomy in Acute Ischaemic Stroke, 2019, with 2023 large-core update — Patient selection
• ACR Appropriateness Criteria: Cerebrovascular Diseases — Stroke and Stroke-Related Conditions, 2023 — Initial imaging

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.

See also: Ischaemic stroke and TIA