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USMLE Step 1Neuroanatomy and lesion localisationEP 08 of 16

Stroke syndromes by artery: ACA, MCA and PCA

Each cerebral artery supplies a patch of cortex, and the deficits of a stroke follow from that patch and from the body map inside it. Place the territory, then read the syndrome.

  • 4:41 video
  • 3 min read
  • 9 sources
  • Published 15 Nov 2026
Video lesson · 4:41 · Watch on YouTubeSeries: Neuroanatomy & Lesion Localisation · @medservatory
Chapters (11)
By the end of this lesson

Predict the deficits of anterior, middle and posterior cerebral artery strokes from the cortical territories each supplies.

The short version

  1. The motor and sensory cortex are body maps: the leg lies medially, the arm and hand over the convexity, the face most laterally.
  2. The anterior cerebral artery (ACA) supplies the leg strip: opposite leg-predominant weakness and sensory loss, with apathy and urinary incontinence.
  3. The middle cerebral artery (MCA) supplies the lateral convexity: opposite face and arm weakness, with aphasia (dominant hemisphere) or neglect (non-dominant hemisphere).
  4. The posterior cerebral artery (PCA) supplies the occipital lobe: an opposite homonymous hemianopia with little or no weakness.

The body map that stroke syndromes by artery depend on

Stroke syndromes by artery are not memorised lists. They follow from two facts: which cortex an artery supplies, and which part of the body that cortex controls. The second fact is the homunculus.

The primary motor and sensory cortex are strips along the precentral and postcentral gyri, laid out as a map of the body.[1][2]

  • The leg sits on the medial surface of the hemisphere, in the paracentral lobule.[1][2]
  • The arm and hand lie over the convexity.[1]
  • The face lies most laterally.[1]

A lesion in one part of the strip therefore weakens one part of the opposite body.

Cortical territories of the ACA, MCA and PCA

Three arteries supply the cortex.[3][4]

Cortical territory of each cerebral artery
ArteryCortical territory
Anterior cerebral artery (ACA)Medial frontal and parietal lobes
Middle cerebral artery (MCA)Lateral surface of the frontal, parietal and temporal lobes
Posterior cerebral artery (PCA)Occipital lobe and medial temporal lobe

Overlay the body map on this table and each syndrome can be predicted: the ACA territory contains the leg strip, the MCA territory contains the arm and face strips, and the PCA territory contains no motor strip at all.[3][4]

ACA stroke: leg weakness, apathy and incontinence

The anterior cerebral artery supplies the leg strip. The result is weakness and sensory loss on the opposite side, worse in the leg than in the arm.[3][5][7]

Frontal damage adds apathy, poor judgement and urinary incontinence.[3][7]

Worked case: the opening patient
  1. A 69-year-old woman has sudden right leg weakness, with the right arm barely affected.
  2. She is apathetic and has wet herself.
  3. Leg-predominant weakness points to the leg strip; apathy and incontinence point to the frontal lobe.
  4. The right side is affected, so the lesion is on the left: a left ACA stroke.

MCA stroke: face and arm weakness, aphasia and neglect

The middle cerebral artery supplies the lateral convexity. You get weakness and sensory loss on the opposite side, worse in the face and arm than in the leg.[3]

  • Dominant hemisphere (usually the left): aphasia.[3]
  • Non-dominant hemisphere: neglect of the opposite side.[3]
  • A homonymous hemianopia can occur.[3]
  • The eyes may deviate toward the side of the lesion.[8]
Worked case: a face and arm deficit
  1. A 56-year-old man has weakness of the left face and arm, ignores the left side of the room, and his eyes look to the right.
  2. Face and arm means the lateral strip, so the middle cerebral artery.
  3. Neglect means the non-dominant hemisphere.
  4. The eyes look toward the lesion, so the lesion is on the right: a right MCA stroke.

PCA stroke: hemianopia without weakness

The posterior cerebral artery supplies the occipital lobe. You get an opposite homonymous hemianopia.[3]

There is no motor strip in the cortical territory, so weakness is little or absent.[3][4]

Lesions that extend further add memory loss from the medial temporal lobe and, when a left-sided lesion reaches the splenium of the corpus callosum, alexia without agraphia.[3][9]

How to localise a stroke by artery, step by step

  1. Find the affected body partLeg-predominant weakness suggests the ACA; face and arm weakness suggests the MCA; a field defect with little weakness suggests the PCA.
  2. Add the cortical featuresApathy and incontinence for the ACA; aphasia or neglect for the MCA; memory loss, or alexia without agraphia from a left lesion reaching the splenium, for the PCA.
  3. Decide the sideThe deficits are on the opposite side of the lesion. Aphasia points to the dominant hemisphere, usually the left; neglect to the non-dominant hemisphere. In an acute hemispheric stroke, deviated eyes usually look toward the lesion.

Practice question

Original · USMLE style
Your turnQB-MS-S1-NEURO-011-01

A 76-year-old man with atrial fibrillation has sudden loss of vision to his left and bumps into objects on his left side. Strength, sensation and speech are normal. Visual field testing shows a left homonymous hemianopia.

Occlusion of which of the following arteries is most likely?
Pick one option. Your answers stay on this device.

Common questions

Which artery causes leg weakness in a stroke?

The anterior cerebral artery supplies the medial cortex that holds the leg strip. An ACA stroke causes opposite weakness and sensory loss that is worse in the leg than in the arm, often with apathy and urinary incontinence.

What are the symptoms of an MCA stroke?

Weakness and sensory loss on the opposite side, worse in the face and arm than in the leg. A dominant-hemisphere lesion also causes aphasia, and a non-dominant lesion causes neglect of the opposite side. A homonymous hemianopia can occur, and the eyes may deviate toward the lesion.

Why does a PCA stroke cause little weakness?

The cortical territory of the posterior cerebral artery is the occipital lobe and medial temporal lobe, which contain no motor strip. It causes an opposite homonymous hemianopia instead.

Where is the leg represented in the motor cortex?

On the medial surface of the hemisphere, in the paracentral lobule. The arm and hand lie over the convexity and the face lies most laterally.

Transcript

Read the full narration, by chapter618 words

0:00A leg that will not move: a case to solve

A 69-year-old woman has sudden weakness of her right leg, while her right arm is barely affected. She is oddly apathetic, and she has wet herself. Which artery? And why the leg and not the arm?

0:14Today's rule and the motor and sensory homunculus

Today: predict the deficits of anterior, middle and posterior cerebral artery strokes from the cortex each one supplies. The primary motor and sensory cortex are strips along the precentral and postcentral gyri, laid out as a map of the body. The leg sits on the medial surface of the hemisphere, in the paracentral lobule. The arm and hand lie over the convexity, and the face lies most laterally.

0:42Three territories: ACA, MCA and PCA

Three arteries supply the cortex. The anterior cerebral artery supplies the medial frontal and parietal lobes. The middle cerebral artery supplies the lateral surface of the frontal, parietal and temporal lobes. The posterior cerebral artery supplies the occipital lobe and the medial temporal lobe. So each artery's deficits follow from its territory, and from the body map inside it.

1:09ACA syndrome: leg-predominant weakness, apathy, incontinence

The anterior cerebral artery supplies the leg strip. You get weakness and sensory loss on the opposite side, worse in the leg than in the arm. Frontal damage adds apathy, poor judgement and urinary incontinence. Our patient: right leg, apathy and incontinence. That is a left anterior cerebral artery stroke.

1:32MCA syndrome: face and arm, aphasia, neglect, gaze

The middle cerebral artery supplies the lateral convexity. You get weakness and sensory loss on the opposite side, worse in the face and arm than in the leg. In the dominant hemisphere, usually the left, you also get aphasia. In the non-dominant hemisphere, you get neglect of the opposite side. A homonymous hemianopia can occur, and the eyes may deviate toward the side of

1:58PCA syndrome: hemianopia, no weakness, alexia without agraphia

the lesion. The posterior cerebral artery supplies the occipital lobe. You get an opposite homonymous hemianopia. There is no motor strip in the cortical territory, so weakness is little or absent. Larger lesions add memory loss from the medial temporal lobe, and, in the left hemisphere, alexia without agraphia.

2:20Worked example: a right MCA stroke

Try one. A 56-year-old man has weakness of the left face and arm, ignores the left side of the room, and his eyes look to the right. Face and arm means the lateral strip, so middle cerebral. Neglect means the non-dominant hemisphere. Eyes toward the lesion: the right middle cerebral artery.

2:42Practice question

Your turn. A 76-year-old man with atrial fibrillation has sudden loss of vision to his left, and bumps into objects on his left. Strength, sensation and speech are normal. Visual field testing shows a left homonymous hemianopia. Occlusion of which artery is most likely? A, the right anterior cerebral artery. B, the right middle cerebral artery. C, the right posterior cerebral artery. D, the left posterior cerebral artery. E, the left middle cerebral artery. Pause here and decide.

3:24Options A, B, D and E ruled out

A is out: that artery supplies the leg strip and the frontal lobe, so you would expect leg weakness, not a field defect. B is out: a middle cerebral artery stroke large enough to cause hemianopia would bring face and arm weakness, sensory loss, or neglect, and none is present. D is out: a left occipital lesion would give a right-sided field defect. E is out: a left middle cerebral artery stroke would also bring aphasia, and it is the wrong side.

3:56The answer: right PCA

So the answer is C. A left homonymous hemianopia without weakness, sensory loss or speech problems is a right occipital lesion: the right posterior cerebral artery.

4:10Recap and next lesson

Three things to keep. One: the anterior cerebral artery is the leg, with apathy and incontinence. Two: the middle cerebral artery is the face and arm, with aphasia from a left-hemisphere lesion, or neglect from a right-hemisphere lesion. Three: the posterior cerebral artery is vision: an opposite homonymous hemianopia, with little weakness. Next, lacunar syndromes.

Sources

Numbers in the text, e.g. [1], point here
  1. Neuroscience Online, Chapter 3: Motor Cortex. nba.uth.tmc.edu/neuroscience/m/s3/chapter03.html
  2. OpenStax. Anatomy and Physiology 2e, 14.2 Central Processing. openstax.org/books/anatomy-and-physiology-2e/pages/14-2-central-processing
  3. MSD Manual Professional Edition. Overview of Stroke (selected stroke syndromes). msdmanuals.com/professional/neurologic-disorders/stroke/overview-of-stroke
  4. TeachMeAnatomy. Arterial Supply of the Brain. teachmeanatomy.info/neuroanatomy/vessels/arterial-supply/
  5. Anterior, middle and posterior cerebral artery syndromes (Wikipedia, secondary source, used only to cross-check). en.wikipedia.org/wiki/Anterior_cerebral_artery_syndrome
  6. Distal left anterior cerebral artery occlusion masquerading as middle cerebral artery syndrome (case report with discussion of typical ACA and MCA syndromes). Cureus 2026. europepmc.org/article/PMC/PMC13189687
  7. Leg-predominant weakness in ACA stroke. BMC Neurology 2021. europepmc.org/article/PMC/PMC8059002
  8. Wrong-way eye deviation during eye opening (case report; states the usual rule of deviation toward a supratentorial lesion). Cureus 2025. europepmc.org/article/PMC/PMC12179422
  9. Alexia without agraphia in left PCA infarction. europepmc.org/article/PMC/PMC12427140

The full source list per claim is in the lesson page. Territory shading and the body map on screen are schematic.

The practice question is original and its patient is synthetic. Every fact is checked against the sources above in independent accuracy reviews. Always follow your local guidelines and your own laboratory’s ranges.

Image credits. Illustrations: Servier Medical Art (smart.servier.com), CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/), adapted (recoloured, outlined, cropped): cerebral arteries. Gray's Anatomy (1918), public domain, via Wikimedia Commons: lateral and medial surfaces of the cerebral hemisphere (Gray 726 and 727), adapted. The territory shading, body map, head diagrams, visual fields and all handwriting are drawn in code (original).

Corrections. None so far. Spotted an error? Email info@medservatory.com with the lesson code MS-S1-NEURO-011.

For exam study only, not medical advice. Read the medical disclaimer.

In this series

Playlist on YouTube
← Previous · EP 07Facial nerve palsy: why the forehead tells you the lesion
  1. EP 01Upper vs lower motor neuron lesions: signs and localisation5:08
  2. EP 02Dorsal column vs spinothalamic tract: where each pathway crosses5:01
  3. EP 03Spinal cord syndromes compared: rebuild each from three tracts5:06
  4. EP 04Cranial nerve nuclei: a brainstem map by level and position5:10
  5. EP 05Brainstem crossed findings: the localisation rule4:50
  6. EP 06Medial vs lateral medullary syndrome: artery, structures and signs5:30
  7. EP 07Facial nerve palsy: why the forehead tells you the lesion4:59
  8. EP 08Stroke syndromes by artery: ACA, MCA and PCA4:41
  9. EP 09Lacunar stroke syndromes: pure motor, pure sensory and more4:54
  10. EP 10Visual pathway lesions and field defects4:42
  11. EP 11Basal ganglia direct and indirect pathways: D1, D2 and movement5:19
  12. EP 12Cerebellar lesion localisation: vermis vs hemisphere4:42
  13. EP 13Brain herniation syndromes: what is squeezed, and where4:56
  14. EP 14CSF flow and hydrocephalus: where the flow fails5:12
  15. EP 15Corticospinal tract: from cortex to anterior horn4:59
  16. EP 16Hypothalamic nuclei and their functions5:24