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Wallenberg – Why No Weakness — SCE Neurology MCQ

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ModerateCerebrovascular DiseaseWallenberg – Why No WeaknessSCE Neurology

A 60-year-old man with a left posterior inferior cerebellar artery (PICA) territory stroke has ipsilateral cerebellar signs (ataxia), ipsilateral Horner syndrome, ipsilateral facial pain and temperature loss, contralateral body pain and temperature loss, dysphagia, hoarseness, vertigo, and nystagmus. He does NOT have weakness. What does the absence of limb weakness indicate?

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Correct answer: E — The corticospinal tract runs in the medullary PYRAMID (anterior medulla) — PICA supplies the lateral medulla, so the corticospinal tract is spared in lateral medullary (Wallenberg) syndrome

Wallenberg syndrome (lateral medullary infarct from PICA or vertebral artery occlusion) characteristically spares the corticospinal tract because it runs in the medullary pyramid (ventral/anterior medulla), which is supplied by the anterior spinal artery, NOT the PICA. The structures damaged in the lateral medulla include: inferior cerebellar peduncle (ataxia), descending sympathetics (Horner), spinal trigeminal nucleus (ipsilateral facial pain/temperature loss), spinothalamic tract (contralateral body pain/temperature loss), nucleus ambiguus (dysphagia, hoarseness), and vestibular nuclei (vertigo, nystagmus). A: Correct observation but the question asks WHY. C: Not MND. D: Consistent with vascular anatomy. E: Weakness is genuinely absent.

Reference: Clinical Neuroanatomy; RCP Stroke Guidelines