Stroke Syndromes & Vascular Localization
A boards-focused map of stroke syndromes: anterior-circulation (ACA/MCA/PCA) cortical patterns and lacunar syndromes, the medial-vs-lateral "rule of 4" for crossed brainstem syndromes (Wallenberg, AICA, medial medullary, locked-in), and the acute CT-then-thrombolysis/thrombectomy management pathway.
Why localization wins points
Stroke questions reward you for turning a deficit into a vascular territory. Each cerebral artery supplies a predictable region of cortex or brainstem, so the pattern of weakness, sensory loss, language, vision, and cranial-nerve findings tells you where the lesion is — and therefore which vessel is occluded. Two rules organize almost every vignette: (1) in the anterior circulation (ACA/MCA), cortical signs (aphasia, neglect, hemianopia, cortical gaze deviation) point to a large-vessel embolus, while their absence with a pure syndrome points to a small-vessel lacune; (2) in the posterior circulation (vertebrobasilar), look for crossed findings — ipsilateral face/cranial-nerve deficits with contralateral body deficits — the signature of a brainstem stroke.
- MCA (most common): contralateral weakness/sensory loss of face and arm > leg; dominant (left) hemisphere → aphasia; non-dominant (right) → hemineglect / anosognosia; contralateral homonymous hemianopia; eyes deviate toward the lesion.
- ACA: contralateral weakness/sensory loss of leg > arm; abulia, urinary incontinence, primitive reflexes (medial frontal lobe).
- PCA: contralateral homonymous hemianopia with macular sparing; dominant-side occlusion → alexia without agraphia; deep branches → thalamic (Déjerine-Roussy) sensory loss/pain.
- Lacunar (chronic HTN / diabetes → lipohyalinosis): pure motor (posterior limb of internal capsule or basis pontis), pure sensory (VPL thalamus), ataxic hemiparesis, dysarthria–clumsy hand — critically, NO cortical signs (no aphasia, neglect, or hemianopia).
- Watershed (ACA–MCA border zone, from systemic hypotension): bilateral proximal arm > leg weakness — the “man in a barrel.”
ACA vs MCA vs PCA
| Feature | ACA | MCA | PCA |
|---|---|---|---|
| Territory | Medial frontal/parietal | Lateral hemisphere | Occipital lobe (± thalamus) |
| Weakness/sensory | Contralateral leg > arm | Contralateral face/arm > leg | Usually spared (sensory loss if thalamus) |
| Signature deficit | Abulia, urinary incontinence | Aphasia (dominant) / neglect (non-dominant) | Homonymous hemianopia, macular sparing |
| Language/vision clue | Personality change | Broca (frontal) vs Wernicke (temporal) | Alexia w/o agraphia (dominant) |
| Eye deviation | — | Toward the lesion | — |
The brainstem: crossed signs & the “rule of 4”
A brainstem infarct produces ipsilateral cranial-nerve findings (the nucleus sits on that side) plus contralateral long-tract findings (corticospinal and spinothalamic fibers cross below the lesion). Gates's “rule of 4” organizes it. The medial brainstem (paramedian branches of the basilar/anterior spinal artery) carries the 4 M’s — Motor/corticospinal tract, Medial lemniscus, MLF, and the Motor nuclei that divide evenly into 12 (III, IV, VI, XII) → contralateral weakness + loss of vibration/proprioception, with an ipsilateral motor cranial-nerve palsy (± internuclear ophthalmoplegia from the MLF). The lateral brainstem (circumferential vessels — PICA, AICA) carries the 4 S’s — Spinothalamic tract, Spinal trigeminal nucleus (Sensory of the face), Sympathetics, and Spinocerebellar tract → crossed pain/temperature loss, ipsilateral facial sensory loss, Horner syndrome, vertigo, and ataxia. Gaze rule: a cortical (FEF) lesion drives the eyes toward the lesion; a pontine (PPRF) lesion drives the eyes away from the lesion — toward the hemiparesis.
Classic brainstem stroke syndromes
| Syndrome | Artery | Ipsilateral findings | Contralateral findings |
|---|---|---|---|
| Lateral medullary (Wallenberg) | PICA / vertebral | Facial pain/temp loss, Horner, ataxia, dysphagia/hoarseness (nucleus ambiguus), vertigo/nystagmus | Body pain/temperature loss |
| Medial medullary | Anterior spinal / vertebral | Tongue deviation toward lesion (CN XII) | Arm/leg weakness + loss of vibration/proprioception |
| Lateral pontine | AICA | Facial paralysis (CN VII), deafness/vertigo (CN VIII), Horner, ataxia | Body pain/temperature loss |
| Locked-in | Basilar (ventral pons) | Quadriplegia + lower CN palsies; only vertical gaze & blinking preserved | (bilateral) |
- “Sudden right face/arm weakness, non-fluent speech, eyes deviated to the left” → left MCA (superior division / Broca). Next best step: non-contrast head CT to exclude hemorrhage, then IV thrombolysis if within the window.
- “Vertigo, hoarseness, hiccups, right-sided facial numbness with left-body loss of pain/temperature, right ptosis/miosis” → lateral medullary (Wallenberg), PICA/vertebral.
- “Painless transient monocular vision loss, like a curtain descending” (amaurosis fugax) → embolus from ipsilateral carotid → next step carotid duplex ultrasound.
- “Hypertensive diabetic with pure right-sided weakness of face, arm, and leg, no aphasia or neglect” → lacunar infarct of the internal capsule.
- “Awake, aware, can only blink and look up/down after basilar occlusion” → locked-in syndrome — do not mistake for coma or a vegetative state.
- Wallenberg / PICA: *“Don’t PICA horse that can’t eat”* — the hallmark is dysphagia/hoarseness (nucleus ambiguus).
- AICA: *“Facial droop means AICA”* — AICA hits CN 7 and 8 (facial paralysis + deafness/vertigo); PICA does not cause facial weakness.
- Lateral medullary sensory pattern: same-side face, opposite-side body loss of pain/temperature (ipsilateral spinal trigeminal + crossed spinothalamic).
- Gaze: eyes look toward a cortical (MCA/FEF) lesion but away from a pontine (PPRF) lesion.
- Homunculus: MCA = face & arm, ACA = leg — the leg hangs over the medial (ACA) side of the motor strip.
- Non-contrast head CT first — exclude hemorrhage before any thrombolytic.
- IV thrombolysis within 4.5 hours of last-known-well with no contraindications: alteplase is the standard, and single-bolus tenecteplase (0.25 mg/kg) is a guideline-endorsed alternative (favored before thrombectomy). BP must be < 185/110 before the bolus and kept < 180/105 for 24 h afterward.
- Mechanical thrombectomy for large-vessel occlusion (proximal MCA/ICA) — up to 24 hours in selected patients with favorable perfusion imaging (DAWN/DEFUSE-3).
- If not a thrombolysis candidate, allow permissive hypertension — only lower BP if > 220/120 (then cautiously).
- Aspirin within 24–48 h (delay 24 h if thrombolytics given); manage glucose, start a high-intensity statin, and pursue the embolic source (carotid duplex, echocardiogram, telemetry for atrial fibrillation).
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