Stroke Territories & ASPECTS
- The brain is plumbed by a handful of named arteries; knowing where each one waters tells you which artery clogged from where the brain went dark.
- The three big front-circulation territories are the anterior, middle, and posterior cerebral arteries (ACA, MCA, PCA). The MCA is the diva — it shows up in your reading room far more than the other two combined.
- ASPECTS is a 10-point scorecard for early MCA stroke on non-contrast CT: you start at 10 and subtract a point for each region that already looks injured.
- A lower ASPECTS means more brain is already lost, which matters because it helps decide who gets clot-pulling treatment and who's past the point of benefit.
When someone rolls in with a face drooping on one side and an arm that won't lift, the question isn't just "is this a stroke?" — it's "which pipe burst, and how much downstream real estate has already gone dark?" Stroke territories answer the first question; ASPECTS helps you put a number on the second.
The brain's plumbing, in plain pipes
Think of the brain as a city and the arteries as the water mains. Each main supplies a specific neighborhood, and when a main clogs, that neighborhood — and only that neighborhood — loses pressure and starts to die. The beauty of this is that brain damage isn't random: it's territorial, like a delivery route. Once you memorize who delivers where, an oddly-shaped dark patch on the scan basically signs the artery's name for you.
The front of the brain runs on the anterior circulation (the carotids feeding ACA and MCA), and the back runs on the posterior circulation (the vertebrals and basilar feeding PCA, brainstem, and cerebellum). They're stitched together by a roundabout at the base called the circle of Willis, which is the body's idea of a backup generator — except, like most backup generators, it's wonderfully reliable right up until the day you actually need it.
- ACA — the midline strip up top. Classic finding: the leg is weaker than the arm.
- MCA — the big lateral wedge covering most of the convexity. Face and arm take the hit, and if it's the dominant side, language goes too.
- PCA — the back, including the occipital lobe. This is the one that steals vision.
Why the MCA gets all the attention
If stroke territories were a high school, the MCA would be the kid who's somehow in every class. It's the largest territory and the most common spot for a big, treatable clot, so a huge share of acute stroke imaging is really MCA-watching. That's exactly why we built a dedicated scoring system for it rather than for the polite, less-frequent neighbors.
"Territory" thinking is your fastest sanity check. If a dark region respects an arterial border, it behaves like a stroke. If it ignores arterial boundaries and crosses wherever it likes, start wondering whether you're looking at something else entirely — see stroke mimics.
ASPECTS: a scorecard for the early MCA stroke
Early stroke is sneaky. In the first hours, a non-contrast head CT can look almost normal, because the damage is subtle — a faint loss of the crisp gray-white boundary, a sulcus that's quietly swollen shut. ASPECTS (the Alberta Stroke Program Early CT Score) exists to make you look on purpose instead of squinting hopefully.
Here's the whole idea: the MCA territory is divided into 10 standardized regions. You start with a perfect score of 10 and subtract one point for every region that already shows early ischemic change. So a 10 means the territory still looks healthy; a low number means a lot of brain has already declared itself injured.
| ASPECTS | What it's telling you |
|---|---|
| 10 | No visible early ischemic change in the MCA territory yet. |
| 8–9 | A region or two already looks injured — small but real. |
| Low (e.g. ≤ a handful) | A large chunk of territory is already lost. |
ASPECTS counts damage, not health. Every point you subtract is a region that already looks dead on CT. Higher is better.
The reason anyone cares about this number is that it feeds the big decision: who benefits from yanking the clot out. If most of the territory is still salvageable (a high score), there's tissue worth rescuing. If the scan already shows a large completed infarct (a low score), the gains from intervention shrink and the risks — like hemorrhagic transformation — loom larger. The exact cutoffs vary by guideline and by what other imaging you have, so think of ASPECTS as one well-calibrated voice in the room, not the referee.
ASPECTS is built for the MCA territory on non-contrast CT — it does not score ACA or PCA strokes, and it isn't meant for the back of the brain. Trying to ASPECTS a posterior-circulation stroke is like grading a swimming race with a stopwatch built for sprinting: wrong tool, confident-looking number.
How to actually use this at the scanner
Read the territory first, the score second. Decide which neighborhood went dark, confirm it respects an arterial border, and only then — if it's an MCA case — walk the 10 regions methodically and tally what's already injured. Doing it in that order keeps you honest, because a tidy number is seductive and it's easy to start counting before you've confirmed you're even looking at a stroke.
If you remember one thing: the territory tells you which artery and where, and ASPECTS tells you how much is already gone. Both feed directly into the clock-driven scramble of the code stroke workflow, where every region you can still save is worth fighting for. For the deeper dive on the disease itself, head to ischemic stroke.