Anterior Circulation Stroke Syndromes

The anterior cerebral circulation — internal carotid artery and its branches, anterior cerebral artery (ACA), middle cerebral artery (MCA), and anterior choroidal artery — supplies the front two-thirds of each cerebral hemisphere and most of the deep gray nuclei. Roughly two-thirds of all ischemic strokes occur in this territory. The clinical syndromes are distinctive and well-defined: each artery’s distribution produces a recognizable pattern that often allows the artery to be named at the bedside before imaging confirms. This page covers the major anterior circulation stroke syndromes.

MCA Territory Stroke

Complete (M1) MCA Occlusion

Affects entire MCA territory — cortical and deep. Features:

• Contralateral hemiplegia: face, arm, leg equally affected (from involvement of motor cortex AND posterior limb of internal capsule via lenticulostriate).
• Contralateral hemisensory loss: full hemibody, all modalities.
• Contralateral homonymous hemianopia: optic radiations or visual cortex.
• Conjugate gaze deviation toward the lesion: frontal eye field damage.
• Dominant side (usually left): global aphasia.
• Non-dominant side (usually right): severe neglect, anosognosia, dressing apraxia.
• Altered mental status: in severe cases.
• Malignant MCA syndrome: in 1-10% of large MCA strokes, edema causes mass effect with rapid neurologic deterioration → decompressive hemicraniectomy is life-saving for selected patients.

Superior Division MCA Stroke

Affects frontal MCA territory (lateral frontal). Features:

• Contralateral hemiparesis: face and arm > leg.
• Contralateral hemisensory loss: face and arm > leg.
• Dominant: Broca aphasia.
• Non-dominant: hemineglect.
• Conjugate gaze deviation toward the lesion (FEF).
• Often no hemianopia (visual cortex not in superior division territory).

Inferior Division MCA Stroke

Affects parietal-temporal MCA territory. Features:

• Contralateral homonymous hemianopia or superior quadrantanopia (Meyer’s loop, temporal radiations).
• Dominant: Wernicke aphasia.
• Non-dominant: severe neglect, anosognosia, constructional apraxia.
• Often subtle motor weakness or none.
• Often missed because absence of obvious hemiparesis.

Deep MCA Stroke (Lenticulostriate / Lacunar)

Small infarcts of the deep perforating vessels supplying internal capsule and basal ganglia. Classical lacunar syndromes:

• Pure motor stroke: contralateral face, arm, leg weakness with NO sensory, visual, or cortical features. Most common. Posterior limb internal capsule.
• Sensorimotor stroke: motor and sensory loss together, no cortical features.
• Dysarthria-clumsy hand: facial weakness, dysarthria, clumsy contralateral hand.
• Ataxic hemiparesis: contralateral hemiparesis + cerebellar-type ataxia on the same side.
• Pure sensory stroke: thalamic VPL/VPM lacunar infarct.

Lacunar syndromes typically reflect small vessel disease (hypertensive arteriolosclerosis, lipohyalinosis); the prognosis is generally favorable for individual events.

ACA Territory Stroke

Less common than MCA. Affects medial frontal and parietal cortex.

Cortical ACA Territory

• Contralateral leg weakness > face/arm. Paracentral lobule (leg representation on medial surface).
• Contralateral leg sensory loss.
• Abulia, apathy: medial frontal involvement.
• Akinetic mutism: if bilateral or anterior cingulate involvement.
• Urinary incontinence: medial frontal.
• Transcortical motor aphasia: dominant side (anterior to Broca area).
• Alien hand syndrome (callosal type): corpus callosum involvement.
• Gegenhalten / paratonia: increased resistance to passive movement.

Recurrent Artery of Heubner

Supplies head of caudate and anterior limb of internal capsule. Infarction → contralateral hemiparesis (anterior limb capsule) + behavioral changes (caudate).

Bilateral ACA / Anterior Communicating Aneurysm

Rupture of anterior communicating artery aneurysm can damage both medial frontal lobes → akinetic mutism, severe abulia, anterograde amnesia (from basal forebrain damage), and behavioral changes. A devastating but often initially under-recognized syndrome.

Anterior Choroidal Artery Stroke

Anterior choroidal artery supplies the posterior limb of internal capsule, optic tract, parts of thalamus, choroid plexus.

Classical triad:

• Contralateral hemiparesis: from posterior limb internal capsule.
• Contralateral hemisensory loss: thalamus.
• Contralateral homonymous hemianopia: from optic tract or radiation involvement.

The combination of “motor + sensory + visual” in a deep stroke is suggestive of anterior choroidal territory.

Internal Carotid Artery (ICA) Disease

ICA Occlusion or Severe Stenosis

• Can produce: complete MCA syndrome (large hemispheric stroke).
• Combined MCA + ACA stroke (entire anterior cerebral hemisphere).
• Watershed stroke (anterior or posterior border zone).
• Multiple small embolic strokes.
• Optic ischemia (amaurosis fugax — transient monocular blindness).
• Bruit on auscultation.
• Hollenhorst plaque (cholesterol embolus visible in retinal artery).

Amaurosis Fugax

Transient monocular blindness — “curtain descending” over vision. Lasts minutes typically. Often a warning of ICA stenosis or atherosclerotic disease; about 30% of patients with amaurosis fugax go on to have a hemispheric stroke without intervention.

Carotid Dissection

• Often in younger patients after neck trauma, manipulation, or sometimes spontaneous.
• Triad: painful Horner syndrome + neck pain + cerebral or retinal ischemia.
• Image with MRA, CTA, or conventional angiography.
• Treatment: anticoagulation (controversial intracranial vs extracranial; antiplatelet alternative).

Posterior Communicating Artery (PCom)

Connects ICA to PCA. Most relevant clinically because of:

• PCom aneurysm: classical site for berry aneurysms. Compresses CN III as it expands or ruptures → pupil-involving third nerve palsy — a neurosurgical emergency.

The Circle of Willis

The arterial ring at the base of the brain connects anterior and posterior circulations, providing collateral flow if one feeding artery is occluded:

• Two ACAs connected by anterior communicating artery.
• Two ICAs (terminal segments).
• Two posterior communicating arteries connecting ICA to PCA.
• Two PCAs connected to basilar.

A “complete” classical circle is found in only a minority of brains. Variations (hypoplastic A1, fetal-type PCA, etc.) affect collateral capacity and clinical patterns.

Aneurysm Patterns

Berry aneurysms preferentially form at branch points of the Circle of Willis. Most common locations:

• Anterior communicating artery (~35%): rupture → bifrontal hemorrhage, possible akinetic mutism, amnesia.
• Posterior communicating artery (~30%): rupture or expansion → pupil-involving CN III palsy.
• Middle cerebral bifurcation (~20%): rupture → temporal/Sylvian hemorrhage, often with intraparenchymal extension.
• Basilar tip (~5%): rupture → severe SAH, brainstem dysfunction.

Recognizing the Artery from the Syndrome

Approach to a Suspected Anterior Circulation Stroke

1. Rapid clinical assessment: NIHSS, last known well, contraindications to thrombolysis or thrombectomy.
2. Non-contrast head CT: rule out hemorrhage, identify early ischemic changes.
3. CT angiography: identify large vessel occlusion, source.
4. If large vessel occlusion within thrombectomy window: emergent neurointerventional referral.
5. If within tPA window (4.5 hours) and no contraindications: IV thrombolytic.
6. MRI brain with DWI (often after acute interventions) for accurate localization.
7. Look for mechanism: cardioembolic (atrial fibrillation, valvular), large artery atherosclerosis (carotid stenosis), small vessel disease (lacunar), dissection, vasculitis, hypercoagulable.
8. Long-term secondary prevention based on mechanism.

🔍 Did You Know?

The classical distinction that cortical MCA stroke spares the leg, while cortical ACA stroke spares the face and arm reflects the somatotopic organization of the motor cortex projected onto the vascular territory. The face and arm representations of motor cortex sit on the lateral surface of the hemisphere (MCA territory); the leg representation extends onto the medial surface in the paracentral lobule (ACA territory). A pure cortical MCA stroke therefore produces face-and-arm weakness with relative leg sparing; a pure cortical ACA stroke produces leg weakness with relative face/arm sparing. Capsular (lenticulostriate) infarction affects face, arm, and leg roughly equally because all the corticospinal fibers from the entire homunculus are tightly packed together as they pass through the internal capsule. This pattern allows the artery to be inferred from the weakness distribution within seconds of examining the patient. The information is also clinically actionable — leg-predominant weakness from a stroke implicates ACA territory and points toward different mechanisms (e.g., anterior communicating aneurysm rupture, hypoperfusion, severe carotid disease) than the more typical MCA territory of cardioembolic stroke. Recognizing the pattern at the bedside refines both the differential diagnosis and the urgency of vascular imaging.

Pitfalls and Pearls

• Cortical MCA stroke spares the leg. ACA spares face and arm. Capsular affects all three equally.
• Eyes deviate TOWARD the lesion in cortical stroke (FEF). AWAY from the lesion in pontine PPRF stroke.
• Aphasia + face/arm weakness: left MCA territory.
• Severe neglect + face/arm weakness: right MCA territory.
• Inferior division MCA stroke can be missed: aphasia or neglect without obvious motor signs.
• Anterior choroidal artery infarction: classical triad of contralateral hemiparesis + hemisensory loss + homonymous hemianopia.
• Amaurosis fugax: transient monocular blindness; investigate carotid disease.
• Painful Horner + neck pain + brain ischemia: ICA dissection.
• Pupil-involving CN III palsy + headache: PCom aneurysm — emergency.
• Akinetic mutism after SAH: anterior communicating artery aneurysm rupture.
• Pure motor stroke: usually lacunar (internal capsule lenticulostriate).
• Pure sensory stroke: thalamic VPL/VPM lacunar.
• Malignant MCA edema: large stroke + deteriorating mental status → consider hemicraniectomy.
• Bilateral ACA stroke: anterior cerebral hypoperfusion (rare) or anterior communicating aneurysm vasospasm/hematoma.
• Watershed strokes: ACA-MCA (man in barrel) or MCA-PCA (Balint features).

References

1. Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 7th ed. Wolters Kluwer; 2017.
2. Caplan LR. Caplan’s Stroke: A Clinical Approach. 5th ed. Cambridge University Press; 2016.
3. Mohr JP, Wolf PA, Grotta JC, et al, eds. Stroke: Pathophysiology, Diagnosis, and Management. 6th ed. Elsevier; 2016.
4. Powers WJ, Rabinstein AA, Ackerson T, et al. Guidelines for the early management of patients with acute ischemic stroke: 2019 update. Stroke. 2019;50(12):e344-e418.
5. Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor’s Principles of Neurology. 11th ed. McGraw-Hill; 2019.