Correlation between clinical outcome and size and site of the lesion in computed tomography guided thalamotomy and pallidotomy.

Fourteen thalamotomies and five pallidotomies were performed in 19 patients with hereditary intention tremor or Parkinson's disease. The target coordinates were determined by a stereotactic computed tomography study using the Laitinen noninvasive stereoadapter. Surgery was done without ventriculography. The patients were assessed 3-12 months later. In a postoperative stereotactic computed tomography study, the positions of the thalamic and pallidal targets were marked, and the coordinates of the center of the lesion were measured in relation to these targets. The volume of the lesion was calculated. In 3 thalamic lesion patients, no lesion could be visualized. The size of the eleven visible thalamic lesions ranged from 4 to 75 mm3 (mean 26), and the size of the 5 pallidal lesions ranged from 28 to 150 mm3 (mean 67). On the average, the center of the lesion was 1.4 mm medial to the position of the anatomical target (p less than 0.002). Neither size nor site of the lesion correlated with the clinical outcome.