Evaluation of gamma thalamotomy for parkinsonian and other tremors: survival of neurons adjacent to the thalamic lesion after gamma thalamotomy

Object. The effects of gamma thalamotomy for parkinsonian and other kinds o f tremor were evaluated. Methods. Thirty-six thalamotomies were performed in 31 patients by using a 4-mm collimator. The maximum dose was 150 Gy in the initial six cases, whic h was reduced to 130 Gy thereafter. The longest follow-up period was 6 year s. The target was determined on T-2-weighted and proton magnetic resonance (MR) images. The point chosen was in the lateral-most part of the thalamic ventralis intermedius nucleus. This is in keeping with open thalamotomy as practiced at the authors' institution. In 15 cases, gamma thalamotomy was t he first surgical procedure. In other cases, previous therapeutic or vascul ar lesions were visible to facilitate targeting. Two types of tissue reaction were observed on MR imaging: a simple oval sha pe and a complex irregular shape. Neither of these changes affected the cli nical course. In the majority of cases, the tremor subsided after a latent interval of approximately 1 year after irradiation. The earliest response w as demonstrated at 3 months. In five cases the tremor remained. In four of these cases, a second radiation session was administered. One of these four patients as well as another patient with an unsatisfactory result underwen t open thalamotomy with microrecording. In both cases, depth recording adja cent to the necrotic area revealed normal neuronal activity, including the rhythmic discharge of tremor. Minor coagulation was per formed and resulted in immediate and complete arrest of the remaining tremor. Conclusions. Gamma thalamotomy for Parkinson's disease seems to be an alter native useful method in selected cases.