Hemiballismus complicating stereotactic thalamotomy.

The pathology of poststereotactic hyperkinesis has been rarely documented and the pathophysiology is still poorly understood. In a case of hemiballismus following thalamotomy for parkinsonism, detailed anatomical studies showed bilateral cortical pseudolaminar necrosis and no involvement of the subthalamic nuclei by the thalamic lesions. The structural and functional effects of surgical lesions upon the preexisting pharmacological abnormalities present in parkinsonism probably constitute the substrate necessary for occurrence of hemiballismus following stereotactic surgery.