ARLY-onset generalized dystonia is a dyskinetic movement disorder that displays a poor response to pharmacological treatment. In the past, surgery has often been considered as a last resort for the most severe cases. Various targets have been selected for ablative or ad- ditive procedures (for example, GPi, thalamus, and subtha- lamic nucleus), but the results have often been incomplete and transient. More recently, DBS of the GPi has been pro- posed as an alternative approach, especially for use in chil- dren. 4,5,18,24 The young age, poor general state of health, and chronic hyperkinetic condition of children with severe dys- tonia made it necessary to develop a short procedure that could be performed with the child in a state of general anes- thesia and during which target localization was based on- ly on 3D MR imaging, without concomitant intraoperative microelectrode recording. Such a procedure has been de- veloped and validated at our center. 4,5,18,24 A strictly defined protocol allowed us to evaluate distortions of brain struc- tures on MR images before and after surgery in daily prac- tice, using the frame as a phantom. Many groups continue to use indirect targeting primari- ly, that is, coordinates calculated by measuring the distance between the target and an internal reference, for example the AC–PC line. This line can be located with the aid of ventriculography, computerized tomography, or MR imag- ing. Distances are then deduced using a human brain atlas, hypothesizing that the proportions given in the atlas are ap- plicable to any individual. It has long been known, however, that there are substan- tial individual variations in coordinates of subcortical nu- J. Neurosurg. / Volume 96 / April, 2002 J Neurosurg 96:673–679, 2002 Comparison of atlas- and magnetic resonance imaging–based stereotactic targeting of the globus pallidus internus in the performance of deep brain stimulation for treatment of dystonia NATHALIE V AYSSIERE, PH.D., SIMONE HEMM, B.M.E., LAURA CIF , M.D., MARIE CHRISTINE PICOT , M.D., NINA DIAKONOVA, PH.D., HASSAN EL FERTIT , M.D., PHILIPPE FREREBEAU, M.D., AND PHILIPPE COUBES, M.D., PH.D. Departments of Pediatric Neurosurgery (Research Group on Movement Disorders in Children) and Biostatistics, University Hospital, Montpellier, France Object. To assess the validity of relying on atlases during stereotactic neurosurgery, the authors compared target coordinates in the globus pallidus internus (GPi) obtained using magnetic resonance (MR) imaging with those de- termined using an atlas. The targets were used in deep brain stimulation (DBS) for the treatment of generalized dys- tonia. Methods. Thirty-five patients, who were treated using bilateral DBS of the GPi, were included in this study. The target was selected on three-dimensional MR images by direct visual recognition of the GPi. The coordinates were automatically recorded using dedicated software. They were translated into the anterior commissure–posterior com- missure (AC–PC) coordinate system by using a matrix transformation process. The same GPi target was defined, based on the locations of brain structures shown in the atlases of Schaltenbrand and Talairach. Magnetic resonance imaging–based GPi target coordinates were statistically compared with the corresponding atlas-based coordinates by applying the Student t-test. A significant difference (p  0.001) was demonstrated in x, y, and z directions between MR imaging–based and Schaltenbrand atlas–derived target coordinates. The comparison with normalized Talairach atlas coordinates demon- strated a significant difference (p  0.01) in the y and z directions, although not in the x direction (p = 0.12). No significant correlation existed between MR imaging–based target coordinates and patient age (p  0.1). No sig- nificant correlation was observed between MR imaging–based target coordinates and patient sex in the y and z direc- tions (p  0.9), although it was significant in the x direction (p  0.05). A significant variation in coordinates and the length of the AC–PC line was revealed only in the y direction (p  0.005). Conclusions. A significant difference was found between target coordinates obtained by direct visual targeting on MR images (validated by postoperative clinical results) and those obtained by indirect targeting based on atlases. KEY WORDS • globus pallidus • stereotactic targeting • magnetic resonance imaging E 673 Abbreviations used in this paper: AC = anterior commissure; BMFDRS = Burke-Marsden-Fahn Dystonia Rating Scale; DBS = deep brain stimulation; GPi = globus pallidus internus; MR = mag- netic resonance; PC = posterior commissure; SD = standard devia- tion; 3D = three-dimensional.