What Are Cerebral Circulation Territories?
The brain's blood supply is divided into distinct vascular territories, each fed by a specific artery — anterior cerebral (ACA), middle cerebral (MCA), and posterior cerebral (PCA) — connected at the base of the brain by the Circle of Willis. Knowing which cortical and subcortical regions each artery supplies is essential for localizing strokes from a patient's symptoms.
Cerebral circulation territories are the brain regions supplied by each major artery: the ACA supplies the medial frontal/parietal lobes (leg/foot motor-sensory cortex), the MCA supplies the lateral hemisphere (face/arm motor-sensory cortex, language areas), and the PCA supplies the occipital lobe and medial temporal lobe (visual cortex, memory structures).
- •Supplied by internal carotid arteries
- •Gives rise to ACA and MCA
- •Supplies about 80% of the cerebral hemispheres
- •MCA territory: face/arm motor-sensory cortex, Broca's/Wernicke's areas
- •ACA territory: medial frontal/parietal lobes, leg/foot cortex
- •Supplied by vertebral arteries feeding the basilar artery
- •Gives rise to PCA, cerebellar arteries, brain stem perforators
- •Supplies brain stem, cerebellum, occipital lobe, medial temporal lobe
- •PCA territory: visual cortex, thalamus, hippocampus (memory)
Step-by-step worked examples
A stroke causes contralateral leg weakness that is worse than arm weakness, with relatively preserved face strength. Which artery territory is most likely involved?
The ACA supplies the medial surface of the frontal and parietal lobes, including the leg/foot area of the motor homunculus. The MCA supplies the lateral surface, including the face and arm areas. Leg-predominant weakness with spared face/arm points to ACA territory infarction.
A patient presents with contralateral face and arm weakness plus expressive aphasia. Which vessel is occluded and why?
Face and arm weakness localize to the lateral motor cortex — MCA territory. Expressive (Broca's) aphasia localizes to the posterior inferior frontal gyrus, also in the MCA territory (dominant hemisphere). Both findings together point to a left MCA occlusion (assuming left-hemisphere language dominance).
A patient has a sudden contralateral homonymous hemianopia with macular sparing but no motor weakness. Which artery is affected?
Homonymous hemianopia results from damage to the visual pathway posterior to the optic chiasm — here, the occipital (visual) cortex. The PCA supplies the occipital lobe; macular sparing occurs because the occipital pole often has dual supply from MCA collaterals. No motor weakness fits, since the PCA does not supply the primary motor cortex — this localizes to a PCA territory infarct.
Flashcards
Quick quiz
Q1.Which artery supplies the leg/foot motor-sensory cortex?
Q2.A stroke causing face/arm weakness plus aphasia most likely involves which artery?
Q3.Which artery supplies the primary visual cortex?
Q4.What structure connects the anterior and posterior cerebral circulations?
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Common mistakes
Assuming MCA territory infarction always causes leg weakness. — Correct: MCA territory covers the lateral cortex (face/arm); leg weakness points more to ACA territory (medial cortex).
Thinking the PCA is part of the anterior (carotid) circulation. — Correct: The PCA arises from the vertebrobasilar (posterior) system, not the internal carotid artery.
Believing the Circle of Willis guarantees full protection from any single vessel occlusion. — Correct: Anatomical variants (an incomplete circle) are common, so occlusion can still cause infarction despite the anastomotic ring.
Confusing homonymous hemianopia with a visual field cut from an eye problem. — Correct: Homonymous hemianopia is caused by a lesion in the visual pathway/cortex behind the chiasm (often PCA territory), not the eye itself.
FAQ
What are cerebral circulation territories?
The specific brain regions supplied by the ACA, MCA, and PCA, which help clinicians localize strokes from symptoms.
What is the formula for identifying which artery is affected by a stroke?
There's no numeric formula — match the deficit pattern (face/arm vs. leg vs. vision/memory) to the known cortical territory of the ACA, MCA, or PCA.
What are examples of cerebral circulation territory strokes?
MCA stroke: face/arm weakness plus aphasia. ACA stroke: leg weakness plus behavioral changes. PCA stroke: visual field loss plus memory deficits.
How do you calculate stroke localization from cerebral circulation territories?
Combine the pattern of motor/sensory loss, language deficits, and visual symptoms with knowledge of which artery supplies each cortical region.