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A theoretical and practical process from microrecording-guided thalamotomy to gamma knife thalamotomy was briefly reviewed. Based on our own experiences of selective thalamotomy with microrecording, we are trying to apply gamma knife to the treatment of movement disorders. An important technical problem is how to determine the exact thalamic target. At first we refer to the posterior commissure and coordinate of the standard atlas for approximately determining the lateral part of the ventral intermediate nucleus. Then the point is further corrected by anatomical landmark (45% of the thalamic length) to compensate the individual difference. A final lesion is made by gamma knife using a 4-mm collimator, 130 Gy in 1 shot. The average delay of clinical improvement is about 6 months after irradiation. Thus far the results are satisfactory, being 80–85% successful without any noticeable complications. Only 3 days of hospitalization with minimal invasion could be a big advantage for the patient. Further technical progress may improve the clinical results in the future. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Gamma thalamotomy has been useful for the treatment of Parkinson’s disease and other movement disorders, but it has disadvantages, such as a delayed clinical effect after irradiation and the inaccuracy of targeting because depth recording is not available. Therefore, we sought to determine the optimum target in gamma thalamotomy based on the results of conventional selective thalamotomy with reference to the AC-PC line. To obtain indirect support for the appropriateness of the optimum target, we performed depth recording around the region of the estimated optimum target based on the results of conventional thalamotomy. Four patients with tremor caused by Parkinson’s disease or essential tremor were used as subjects after they gave their fully informed consent. The targets were determined as points 6–8 mm anterior to the posterior commissure, 4–6 mm dorsal to the level of the intercommissural line, and 15–17 mm lateral from the midline. Rhythmic discharge time-locked to tremor and/or kinesthetic neurons were found within the expected target area in all patients. Finally, in all cases, the tremor was abolished without complications after coagulative lesions were made with dual coagulation needles to cover the supposed Vim zone according to the depth recording. We considered that the target point determined in the same way as in gamma thalamotomy is suitable from an anatomophysiological perspective. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]