A 58-year-old man develops sudden right-sided hemiplegia with right lower facial weakness and leftward tongue deviation on protrusion. Sensation is intact bilaterally. Where is the lesion?

• A Left medullary pyramid plus left hypoglossal fascicles ✓
• B Left internal capsule (posterior limb)
• C Right medullary pyramid
• D Left basis pontis with involvement of left corticospinal and left corticobulbar fibres

Explanation

Right hemiplegia with ipsilateral tongue deviation indicates a medullary lesion below the pyramidal decussation on the left side: the left pyramid carries crossed motor fibres (causing contralateral right hemiplegia), and the left hypoglossal fibres, damaged before they exit, cause left XII palsy manifesting as leftward tongue deviation. Right lower facial weakness does not fit a purely medullary location — in this question the dominant finding pointing to the answer is right hemiplegia + left XII palsy = left medullary pyramidal plus hypoglossal root lesion (Déjerine inferior alternating hemiplegia). The facial nerve nucleus is pontine; its involvement would instead indicate a pontine lesion.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.