The Alberta Stroke Program Early CT Score (ASPECTS) was introduced to make early ischemic change on non-contrast CT reproducible and quantitative, rather than a gestalt impression of "a lot" or "a little" hypoattenuation. Before its description, the only widely used rule was the qualitative "greater than one-third of the MCA territory" threshold, which proved poorly reproducible between readers. ASPECTS replaced that with a simple, region-based 10-point system that correlated with functional outcome and symptomatic hemorrhage after intravenous thrombolysis.1 Two decades later it remains the dominant CT imaging metric in acute stroke triage and a near-universal entry in thrombectomy trial eligibility criteria.

How the score is built.

Start at 10 and subtract one point for each region showing early ischemic change — defined as parenchymal hypoattenuation or loss of the normal gray–white distinction, not mass effect or sulcal effacement alone. The score is applied only to the MCA territory and is read across two standardized axial levels:2

  • Basal ganglia level (at the level of the thalamus and basal ganglia) — seven regions: caudate, lentiform nucleus, internal capsule, insular ribbon, and the inferior MCA cortical zones M1, M2, M3.
  • Supraganglionic level (just rostral, above the basal ganglia) — three regions: the superior MCA cortical zones M4, M5, M6.

M1–M3 are the anterior, lateral, and posterior cortical segments at the ganglionic level; M4–M6 are the corresponding segments immediately above it. A score of 10 is a normal scan; 0 means ischemic change throughout the entire MCA territory. The score is meant to be read on the early, hyperacute CT — its prognostic value is anchored to the pre-treatment scan, not a follow-up study.

Bedside pearl

Each region is one point regardless of size — the tiny caudate counts the same as the large M5 cortical zone. ASPECTS counts how many regions are involved, not how much of any one region. Widen the window settings (a narrow stroke window of roughly 30–40 HU width / 30–35 HU level) to make subtle gray–white loss visible.

What the score predicts.

In the original derivation cohort of patients treated with intravenous alteplase within 3 hours, a lower baseline ASPECTS was inversely associated with both worse 3-month functional outcome and a higher risk of symptomatic intracerebral hemorrhage.1 The score behaves as a surrogate for established, non-salvageable core — the more regions already hypoattenuated, the less tissue is likely to be rescued by reperfusion and the more fragile that tissue is when flow returns. That dual signal — less benefit, more bleeding risk at low scores — is why ASPECTS became embedded in treatment thresholds rather than staying a purely descriptive tool.

The shifting thrombectomy threshold.

For years the practical cut-point for endovascular therapy was ASPECTS ≥6: most pivotal early-window thrombectomy trials enrolled predominantly higher scores, and many centers treated ≤5 as a relative contraindication because of presumed reperfusion-injury risk in a large established core. That equipoise was directly tested by a cluster of large-core trials. SELECT2 randomized patients with large ischemic core, including those with ASPECTS in the 3–5 range, and showed better functional outcomes with thrombectomy plus medical care than with medical care alone.3 ANGEL-ASPECT, conducted in China, similarly enrolled patients with large infarct (including low ASPECTS) and found a benefit of endovascular therapy.4 Companion trials in this large-core wave (for example RESCUE-Japan LIMIT and TENSION)5,6 pointed in the same direction, and the seed for this page reflects that the eligibility envelope has widened to ASPECTS 3–5 in selected patients.

Two cautions are worth stating plainly. First, these trials still typically excluded the very lowest scores (most did not enroll ASPECTS 0–2), so "large core is treatable" is not the same as "any core is treatable." Second, benefit in these populations was real but on average more modest, and came with a higher absolute hemorrhage rate — selection still matters. Guidelines and individual institutional protocols vary on exactly where to draw the line and which patients to treat, so confirm your local pathway rather than assuming a single universal cutoff.

Where readers go wrong.

ASPECTS is only as good as the regions you actually inspect. The two most frequently missed regions are the caudate and the insula — both are small, both lose their normal margins early, and both are easy to skip when the eye is drawn to the obvious cortical change. Deliberately interrogate the insular ribbon and the caudate head on every scan. Inter-rater agreement is moderate at best for human readers, which is the gap automated tools aim to close.

Pitfall

Do not treat the automated number as ground truth. Software such as RAPID and Brainomix reduces inter-rater variability and speeds triage, but it can be fooled by chronic infarct, leukoaraiosis, motion, and beam-hardening artifact — sometimes scoring an old lacune or white-matter disease as acute change. Always overread the source images yourself; the algorithm informs the decision, it does not make it.

Practical use at the bedside.

Treat ASPECTS as one axis of a multi-axis decision: time from last-known-well, clinical deficit (NIHSS), vessel occlusion site on CTA, collateral status, and — in extended windows — perfusion mismatch. A modest ASPECTS in a young patient with excellent collaterals and a salvageable penumbra is a very different proposition from the same number in an elderly patient with poor collaterals. Document the score, the level at which you read it, and which regions you scored down, so the next reader can reconcile their read with yours. This page is for clinician education and does not substitute for individualized clinical judgment or your institution's reperfusion protocol.