## Why Ventral posterolateral (VPL) nucleus is right The clinical presentation of pure sensory stroke affecting the contralateral face, arm, and leg with preserved motor function is the hallmark of a lacunar infarct involving the VPL nucleus of the thalamus. The VPL nucleus is the major relay station for body sensation (spinothalamic tract and dorsal column-medial lemniscus pathways) to the primary somatosensory cortex. Infarction in this nucleus produces the classic lacunar syndrome of "pure sensory stroke" without motor deficit. The patient's intact motor examination excludes involvement of the ventral lateral nucleus, which would cause motor weakness. This is a key anatomical-clinical correlation tested in neurology board examinations. ## Why each distractor is wrong - **Lateral geniculate nucleus (LGN)**: Relays visual information; infarction would cause visual field defects or blindness, not sensory loss in the face, arm, and leg. The patient has no visual complaints. - **Medial geniculate nucleus (MGN)**: Relays auditory information from the inferior colliculus; infarction would cause hearing loss or auditory deficits, not somatosensory loss. No auditory symptoms are present. - **Ventral lateral (VL) nucleus**: Relays motor information from cerebellum and basal ganglia to motor cortex; infarction would produce motor weakness or ataxia, not pure sensory loss. This patient has preserved motor strength. **High-Yield:** VPL nucleus infarction → pure sensory stroke (contralateral face, arm, leg sensory loss without motor deficit); VL nucleus infarction → motor deficit; LGN → visual loss; MGN → auditory loss. [cite: Gray's Anatomy 42e Ch 22; Harrison 21e Ch 426]
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