A 68-year-old hypertensive man suddenly develops violent, flinging movements of the LEFT arm and leg. CT shows a small haemorrhage in the basal ganglia region. Which structure is most likely involved?

• A Left red nucleus
• B Left subthalamic nucleus
• C Right globus pallidus externa
• D Right subthalamic nucleus ✓

Explanation

Contralateral hemiballismus results from a lesion of the subthalamic nucleus, most often a small lacunar haemorrhage or infarct. The subthalamic nucleus exerts inhibitory control over the globus pallidus externa through indirect pathway output, so its loss releases violent involuntary movements on the opposite side of the body. The red nucleus produces tremor and rubral signs, not ballistic movements, and the globus pallidus externa itself does not cause hemiballismus when damaged directly.

Reference: Gray's Anatomy, 42nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.