Background The last decade has witnessed a renaissance of functional stereotactic neurosurgery in the treatment of patients with movement disorders, especially advanced Parkinson’s disease (PD), essential tremor (ET) and dystonia. Ablative lesions such as thalamotomy and pallidotomy have been gradually replaced by the technique of chronic deep brain stimulation (DBS) applied to targets in the basal ganglia and thalamus, and assumed to be more lenient to the brain than stereotactic radiofrequency lesions. Since the aim of functional neurosurgery is to alleviate symptoms of these chronic, progressive, non-fatal diseases, and to improve life quality of the patients, it is imperative that the surgical procedures remain safe and do not result in complications mitigating any anticipated positive effect of the surgery on the symptoms of the disease. Aim The aim of this thesis is to evaluate, compare and analyse the safety of various surgical procedures used to treat patients with movement disorders, and to document side effects and complications both peri operatively and in a long term follow-up. Further to compare the effects of pallidotomy and pallidal DBS, and to evaluate the longterm efficacy of Vim-DBS. Method 256 consecutive surgical procedures, 129 DBS and 127 stereotactic lesions, were reviewed with respect to complications in 197 treated patients. In a series of 119 patients operated on with DBS during a 10 year period, the occurrence of hardware related complications (infection, breakage, erosion etc) was documented and analysed. Additionally, the interference of external magnetic field with the stimulation was documented. In one patient operated on with subthalamic nucleus DBS, a highly unusual and unexpected psychiatric side effect was carefully analysed. In 5 patients operated on with both methods (lesion and DBS) on each hemisphere, respectively, the effect and side effects of each method were compared. The long term effect and side effects of thalamic DBS was analysed in a series of patients with ET followed for 7 years. Results There were no deaths and few severe neurological complications in this material. Unilateral ablative lesions in the pallidum were well tolerated by patients with advanced PD, while for tremor, thalamic DBS was much safer than thalamotomy, even if its effect on certain aspects of tremor could show some decrease of efficacy over time. Some of the side effects of lesioning are transient while most but not all side effects of DBS are reversible. Hardware-related complications were not uncommon especially in the early “learning curve” period, and the DBS technique, being a life-long therapy, will necessitate a life long follow up of patients. Provided safety protocols are followed and provided patient’s and carer’s education and awareness, external electromagnetic interference should not constitute a risk for patients with DBS. PD patients undergoing STN DBS should be carefully selected to avoid psychiatric or cognitive side effects, due to this brain target´s proximity to, and involvment in, non-motor associative and limbic circuitry. Conclusions In terms of mortality and morbidity, modern stereotactic neurosurgery for movement disorders, both ablation and DBS, is a safe procedure even in advanced stages of disease. Symptoms of PD, ET and dystonia can be alleviated mainly with DBS and even unilaterally with pallidal lesions, at the expense of, in most cases, minor side-effects.

Background: The birth of stereotactic functional neurosurgery in 1947 was to a great extent dependent on the development of ventriculography. The last decades have witnessed a renaissance of functional stereotactic neurosurgery in the treatment of patients with movement disorders. Initially, these procedures were largely based on the same imaging technique that had been used since the birth of this technique, and that is still used in some centers. The introduction of new imaging modalities such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) provided new potentials, but also new challenges for accurate identification and visualisation of the targets in the basal ganglia and the thalamus with an urge to thoroughly evaluate and optimize the stereotactic targeting technique, as well as evaluate accurately in stereotactic space the location and extent of stereotactic Radiofrequency (RF) lesions and the position of deep brain stimulation (DBS) electrodes. Aims: To study the differences between CT and MRI regarding indirect atlas coordinates in thalamic and pallidal procedures and to evaluate and validate visualisation of the pallidum and the subthalamic nucleus in view of direct targeting irrespective of atlas-derived coordinates. Furthermore, to evaluate the contribution of RF parameters on the size of stereotactic lesions, as well as the impact of size and location on clinical outcome. Method: The coordinates in relation to the landmarks of the 3rd ventricle of the targets in the pallidum and ventrolateral thalamus were compared between CT and MRI in 34 patients. In another 48 patients direct visualization  of the pallidum was evaluated and compared to indirect atlas based targeting. The possibility and versatility of visualizing the Subthalamic Nucleus (STN) on short acquisition MRI were evaluated in a multicentre study, and the use of alternative landmarks in identification of the STN was demonstrated in another study. In 46 patients CT and MRI were compared regarding the volume of the visible RF lesions. The volume was analysed with regard to coagulation parameters, and the location and size of the lesions were further evaluated concerning the clinical outcome. Results:Minor deviations were seen between MRI and  CT coordinates of brain targets. The rostro-caudal direction of these deviations were such that they would be easily accounted for during surgery, why MRI can obviate the need for CT in these procedures. MRI using a proton density sequence provided detailed images of the pallidal structures, which demonstrated considerable inter-individual variations in relation to the landmarks of the 3rd ventricle. By using a direct visualization of the target, each patient will act as his or her own atlas, avoiding the uncertainties of atlas-based targeting. The STN could be visualized on various brands of MRI machines in 8 centers in 6 countries with good discrimination and with a short acquisition time, allowing direct visual targeting. The same scanning technique could be used for postoperative localization of the implanted electrodes. In cases where the lateral and inferior borders of the STN cannot be easily distinguished on MRI the Sukeroku sign and the dent internal-capsule-sign signs might be useful. The volume of a stereotactic RF lesion could be as accurately assessed by CT as by MRI. The lesion´s size was most strongly influenced by the temperature used for coagulation. The lesions´ volumes were however rather scattered and difficult to predict in the individual patient based solely on the coagulation parameters. For thalamotomy, the results on tremor was not related to the lesion´s volume. For pallidotomy, larger and more posterior-ventral lesions had better effect on akinesia while effects on tremor and dyskinesias were not related to size or location of the lesions. Conclusions: The minor deviations of MRI from CT coordinates can be accounted for during surgery, why MRI can obviate the need of CT in these procedures. Direct visualized targeting on MRI of the pallidum is superior to atlas based targeting. The targets in the pallidum and the STN, as well as the location of the electrodes, can be well visualized with short acquisition MRI. When borders of the STN are poorly defined on MRI the Sukeroku sign and the dent internal-capsule-sign signs proved to be useful. The volumes of RF lesions can be accurately assessed by both stereotactic thin slice CT and MRI. The size of these lesions is most strongly influenced by the temperature of coagulation, but difficult to predict in the individual patient based on the coagulation parameters. Within certain limits, there were no clear relationships between lesions´ volume and location and clinical effects of thalamotomies and pallidotomies.