Ischemic Stroke for Step 1: Vascular Territories & Timing

Creator: Progress Note
Published: 2026-08-27
Keywords: ischemic stroke, ischemic stroke usmle, stroke vascular territories, mca vs aca stroke, lacunar stroke, wallenberg syndrome pica, stroke histology timeline red neurons, broca vs wernicke aphasia, tpa window, watershed infarct

bolt The 60-second version

check_circleACA: contralateral leg weakness and numbness. MCA: contralateral face and arm weakness and numbness, aphasia (dominant hemisphere) or neglect (nondominant), eyes deviate toward the lesion.
check_circlePCA: contralateral homonymous hemianopia with macular sparing.
check_circleLacunar strokes (lenticulostriate arteries, hypertension): pure motor (internal capsule) or pure sensory (thalamus) deficits without cortical signs.
check_circlePICA (lateral medullary syndrome): dysphagia, hoarseness, ipsilateral facial and contralateral body pain-temperature loss, Horner syndrome, vertigo.
check_circleHistology: red neurons at 12–24 hours, neutrophils at 1–3 days, microglia at 3–7 days, then gliosis and a cystic cavity (liquefactive necrosis).
check_circleAcute care: noncontrast CT to exclude hemorrhage, then IV thrombolysis within 4.5 hours of onset when eligible, and thrombectomy for large-vessel occlusion.

target What you'll be able to do · aligned to USMLE Step 1 · Nervous System

NEUROLocalize strokes to the ACA, MCA, PCA, lacunar, and brainstem territories.
NEUROIdentify the mechanisms of ischemic stroke.
PATHDescribe the histologic timeline of cerebral infarction.
NEUROOutline acute management and secondary prevention.

How stroke is tested on Step 1

Map the deficit to the artery.

Artery	Territory	Classic deficits
Anterior cerebral (ACA)	Medial frontal and parietal lobes	Contralateral leg weakness and sensory loss; urinary incontinence
Middle cerebral (MCA)	Lateral hemisphere	Contralateral face and arm > leg; Broca or Wernicke aphasia (dominant); neglect (nondominant)
Posterior cerebral (PCA)	Occipital lobe, thalamus	Contralateral hemianopia with macular sparing
Lenticulostriate (lacunar)	Internal capsule, basal ganglia, thalamus	Pure motor or pure sensory stroke
PICA	Lateral medulla	Wallenberg syndrome: dysphagia, hoarseness, crossed pain-temperature loss, Horner
AICA	Lateral pons	Ipsilateral facial paralysis, hearing loss, vertigo
Anterior spinal	Medial medulla	Contralateral hemiparesis, ipsilateral tongue weakness
Basilar	Pons	Locked-in syndrome

Broca aphasia (inferior frontal gyrus): nonfluent, comprehension intact. Wernicke aphasia (superior temporal gyrus): fluent but meaningless, poor comprehension.

Causes of ischemic stroke

Find the source to choose secondary prevention.

Stroke mechanisms. Embolic strokes often affect the MCA and can become hemorrhagic when the vessel reopens.

Pathology timeline

The brain undergoes liquefactive necrosis.

Infarct timeline. Neurons in hippocampus (CA1), Purkinje cells, and neocortex are most vulnerable to global ischemia.

Treatment and prevention

Rule out bleeding first.

Imaging: noncontrast head CT excludes hemorrhage; early ischemic stroke may look normal on CT, while MRI diffusion-weighted imaging shows it within minutes.
Reperfusion: IV thrombolysis (alteplase or tenecteplase) within 4.5 hours for eligible patients; mechanical thrombectomy for large-vessel occlusion.
Secondary prevention: antiplatelet therapy, high-intensity statin, blood pressure control; anticoagulation for atrial fibrillation; carotid endarterectomy for symptomatic severe stenosis.

Worked example

Use crossed findings.

functions Worked example — vertigo and hoarseness

A patient has sudden vertigo, hoarseness, and trouble swallowing. There is loss of pain and temperature sensation on the left face and the right side of the body, and a small left pupil with ptosis. Which artery is occluded?

Crossed pain-temperature loss (face on one side, body on the other) means a brainstem lesion.
Hoarseness and dysphagia point to the nucleus ambiguus in the lateral medulla.
Left Horner syndrome reflects the descending sympathetic fibers in the lateral medulla.
The lateral medulla is supplied by the posterior inferior cerebellar artery.

Answer. Left PICA (lateral medullary or Wallenberg syndrome).

Next in the roadmap

TIA

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quiz Test yourself

Quick check — 3 questions

1. Right face and arm weakness with nonfluent speech and intact comprehension. Occluded artery?

2. Neutrophils fill an infarct. Time since stroke?

3. Pure motor hemiparesis without aphasia or visual loss suggests a lesion in the:

Frequently asked questions

Which artery causes leg-predominant weakness?expand_more

The anterior cerebral artery.

What kind of necrosis occurs in the brain after stroke?expand_more

Liquefactive necrosis.

What causes lacunar strokes?expand_more

Hyaline arteriolosclerosis of small penetrating arteries, usually from chronic hypertension.

Why get a noncontrast CT first?expand_more

To exclude hemorrhage before giving a thrombolytic.

References & further reading

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