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Where's the neurological lesion in hemiballism? Is it a unilateral brain/brainstem lesion or a diffuse one? And if unilateral, which side (ipsilateral/contralateral)?
 

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Hemiballismus is due to a lesion in the contralateral subthalamic nucleus (part of the basal ganglia), mostly due to hypertensive crises. It presents with 'wild' swinging of the extremities (contralateral to the lesion).


In the illustration, the subthalamic nucleus (STN) is in yellow.

Source: Wikipedia.
 

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Thanks friend, just found now in HY Neuro that the lesion is the STN, but it doesn't state it side :))
Remember that motor neurons (cortico-spinal tract) cross in the pyramidal decussation of the medulla, so all deficits will be contralateral. So if something is seen on the left side, for example wild flailing of the left arm or leg in hemiballismus, then that would mean the lesion in the STN is on the right side. The same goes for the face, so in a stoke if the right side of the face is drooping, the lesion is on the left side of the brain. An important distinction is Bell's Palsy, where the ipsilateral nerve is affected (because the virus infects the facial nerve after it has crossed). If you remember this, then you never have to memorize sides!
 
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