Book: Stereotactic Atlas of the Human Thalamus and Basal Ganglia

Anne Morel

Chapter 1 Opening – A New Anatomical Framework for Stereotactic Functional Neurosurgery and Neuroimaging

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The importance of the thalamus, basal ganglia and related cortical networks in sensory, motor, cognitive and emotional experiences is well recognized. The complexity of the circuitry is far from being fully comprehended, although great progress has already been made through recent developments in all fields of neuroscience, whether experimental or clinical. In the clinical environment, the increasing number and accuracy of noninvasive methods for exploring the human brain provide insights into normal as well as pathological conditions. Knowledge of the location of the cerebral insult and/or the system affected is of prime importance not only to determine the cause of the disorder, but also for surgical interventions aimed at removing or modulating abnormally functioning brain structures. In surgical treatment of chronic functional disorders [e.g., Parkinson’s disease (PD), neurogenic pain], deep brain structures such as the thalamus and basal ganglia are reached stereotactically, with procedures allowing the surgeon to selectively target an anatomically defined nuclear or fiber system (Fig. 1 in chap. 7). Today, stereotactic surgery is generally guided by magnetic resonance imaging (MRI) to plane electrode trajectory and transfer target coordinates defined on an anatomical atlas onto individual patients brain images, using a common 3D stereotactic reference system. Recent progress in MRI resolution allows better visualization of some structures of interest as well as anatomical landmarks in the vicinity of the target. In particular, visualization of major subdivisions of the basal ganglia (striatum and pallidum) and more recently, of the subthalamic nucleus (STh) in specific MRI sequences has lead more neurosurgeons to rely on these images to directly target the internal pallidum or STh in patients undergoing stereotactic surgery for PD (1–4). MRI measurements (automated or manual) also are useful to study large samples of the whole thalamus or particular nuclei (e.g., pulvinar and mediodorsal nuclei) in controls as well as in pathological cases, such as in schizophrenic subjects (5–7). Nevertheless, these images give only approximate contours of some of these structures, such as for the ventral limit of the STh with adjacent substantia nigra (SN). Furthermore, fine histological structures such as precise delimitation of individual nuclei in the thalamus or anatomo-functional territories in the basal ganglia are still beyond MR image resolution. One has still to rely on indirect targeting, that is, by transfer of detailed histological maps obtained from 3D anatomical atlas onto individual patients’ brain images. Accurate anatomical localization in the field of stereotactic surgery reduces operative time and, thus, the hazard of complication by minimizing the tissue volume to be explored physiologically for final identification of the target site. Anatomical and stereotactic precision is even more critical in cases of radiosurgery [e.g., gamma knife radiosurgery (8–11)] or other neuradiological approaches where there is no electrophysiological verification of the target. These interventions also require evaluation of the degree of interindividual anatomical variability of subcortical structures, which can be adequately performed only when the different brains are cut stereotactically, thus minimizing the risk of under- or overestimating interindividual anatomical variations. Stereotactic atlases are needed not only for precise targeting in functional neurosurgery, but also for accurate projections of peroperative physiological data (stimulations, microelectrode recordings) (12–17), localization of therapeutic lesions or high frequency stimulation (HFS) sites (18–20), localization of vascular damages (21–22), or diffusion tensor imaging (DTI) data (23–24).

Informa Healthcare USA, Inc., New-York, 2007. ISBN : 9780824728946.