A 55-year-old man develops sudden onset diplopia and ipsilateral facial numbness with contralateral hemiplegia. MRI shows a lesion in the pons. Which specific tract is most likely interrupted to cause the contralateral hemiplegia in this case?
- A Medial lemniscus
- B Spinothalamic tract
- C Corticospinal tract in the basis pontis ✓
- D Rubrospinal tract
Explanation
This clinical picture is a crossed syndrome (Millard-Gubler syndrome) — ipsilateral CN VI and VII palsy plus contralateral hemiplegia — caused by a ventral pontine lesion. The contralateral hemiplegia results from interruption of the corticospinal tract as it courses through the basis pontis before crossing at the medullary pyramidal decussation. The medial lemniscus carries dorsal column information and its interruption causes contralateral loss of touch/proprioception, not hemiplegia. The spinothalamic tract is dorsolateral to the lemniscus. The rubrospinal tract is rudimentary in humans.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.