Cerebral Artery Territory Quiz
Stroke deficits follow plumbing, not function. Once you know which artery supplies which territory, a confusing set of symptoms collapses into one vessel. This quiz gives you the deficits and asks which artery is occluded, then shows the territory on a 3D brain.
The three major territories
The anterior cerebral artery supplies the medial surface of the frontal and parietal lobes. Because the leg sits on the medial motor strip, an ACA stroke causes weakness that is worse in the leg than the arm or face.
The middle cerebral artery supplies the lateral convexity, which contains the face and arm motor and sensory cortex, plus the language areas on the dominant side. An MCA stroke causes face-and-arm-predominant weakness, with aphasia on the left or neglect on the right. It is by far the most common territory.
The posterior cerebral artery supplies the occipital lobe and the medial temporal lobe. A PCA stroke causes a homonymous hemianopia, often with macular sparing, and can cause memory deficits when the hippocampus is involved.
Brainstem and the crossed syndromes
The vertebrobasilar system supplies the brainstem and cerebellum, and its strokes produce the crossed syndromes. The posterior inferior cerebellar artery causes lateral medullary syndrome — ipsilateral facial sensory loss, Horner syndrome and ataxia, with contralateral body sensory loss and preserved strength.
The rule that makes brainstem strokes tractable: cranial nerve signs localize to the same side as the lesion, long-tract signs to the opposite side. Find both and you have both the level and the side.
Watershed zones
Between territories are the watershed zones, perfused last and damaged first in global hypotension. Their signature is proximal weakness affecting shoulders and hips while sparing hands and feet — the man-in-a-barrel pattern — which points to systemic hypoperfusion rather than a single blocked vessel.
Common questions
How do you tell an ACA stroke from an MCA stroke?
By which part of the body is weakest. The ACA supplies the medial cortex where the leg is represented, so ACA strokes are leg-predominant. The MCA supplies the lateral cortex where the face and arm are represented, so MCA strokes are face and arm predominant and often include aphasia or neglect.
Which artery causes homonymous hemianopia?
The posterior cerebral artery, which supplies the occipital lobe and the primary visual cortex. Macular sparing is common because the occipital pole often receives collateral supply from the middle cerebral artery.
What is a watershed stroke?
An infarct at the border between two arterial territories, caused by global hypoperfusion rather than occlusion of one vessel. It classically produces bilateral proximal weakness of the shoulders and hips with the hands and feet spared.