A 62-year-old hypertensive man suddenly develops violent, flinging, involuntary movements of his left arm and leg. MRI shows a small infarct in the right diencephalon. Which structure is damaged?
- A Right ventrolateral nucleus of the thalamus
- B Left globus pallidus externa
- C Right subthalamic nucleus ✓
- D Right substantia nigra pars compacta
Correct answer: C. Right subthalamic nucleus
Explanation
Hemiballismus, wild flinging movements of the contralateral limbs, classically results from a lesion of the contralateral subthalamic nucleus, usually a small hypertensive infarct. The subthalamic nucleus normally exerts excitatory drive on the globus pallidus interna; its loss disinhibits the thalamus. A thalamic VL lesion causes sensory loss or tremor, and Parkinsonism follows substantia nigra pars compacta damage, not ballistic movements.
Reference: Snell's Clinical Neuroanatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.