Chronic thalamic stimulation with three-dimensional MR stereotactic guidance.

PURPOSE To report a method of electrode implantation in the ventralis intermedius nucleus of the thalamus for the treatment of tremor using a 3-D stereotactic MR imaging technique.

METHODS Five patients (three men and two women; mean age, 59 years) with medically refractory tremor had intrathalamic implantation of a stimulating electrode. Stereotactic MR imaging was performed on a 1.5-T unit equipped with an MR-compatible Leksell G stereotactic frame fixed to the patient's head. Calculation of the coordinates of the theoretical target was based on the coordinates of the anterior commissure, the posterior commissure, and the midline sagittal plane as determined via stereotactic MR imaging. During the surgical procedure, the best position for the stimulating electrode was determined by electrophysiological and clinical studies. Postoperative MR control studies were done in all cases to verify the position of the electrode.

RESULTS Stereotactic MR imaging allowed precise implantation of the stimulating electrode in all patients. Electrode stimulation produced a 90% reduction of the tremor in two patients, an 80% and 70% reduction in one patient each, and a persistent microthalamotomy-like effect in the fifth patient. Examination of the MR control studies showed that mean error in the positioning of the electrodes was 0.77 +/- 0.6 mm (mean +/- SD) in the x direction and 0.80 +/- 1.02 mm in the y direction.

CONCLUSION Although our series is relatively small, the precision achieved with stereotactic MR imaging proves that it can be used with confidence for precise functional neurosurgical procedures.