Pallidotomy: Theory and technique

Pallidotomy, the surgical destruction of portions of the globus pallidus, is now frequently performed to treat patients with Parkinson's disease. As a consequence of dopamine loss in the brain of a patient with Parkinson's disease, the globus pallidus internal segment (GPi) is overactive. A lesion in the GPi compensates for this and partially alleviates most of the motor signs of Parkinson's disease, as well as levodopa-induced dyskinesias. The goal in pallidotomy is to produce a lesion of the whole sensorimotor (posterolateral) region of the GPi without producing a lesion in the external pallidum, nonmotor areas of the GPI, optic tract, or corticospinal tract. To achieve this goal, magnetic resonance imaging (MRI)-based stereotactic localization, microelectrode recording, and macrostimulation are used in concert for precise localization of the GPi and surrounding structures. Based on the known patterns of neuronal activity and receptive fields in the basal ganglia, microelectrode recording is used to construct a detailed three-dimensional map of the GPi and to identify the motor-controlling subdivision of this nucleus. Multiple microelectrode tracks, rather than a single track, are used to maximize accuracy. Pallidotomy is performed with a radiofrequency thermocoagulation probe, at multiple depths along multiple parallel tracks, to contour the lesion according to the microelectrode derived map. Precise lesion placement is important for the best long-term outcome.