Objective: Validate an MRI procedure based on visible anatomical landmarks to target the STN
Material and Methods: 26 Parkinsonian patients were selected for DBS. Surgery was performed with a CRW frame (Radionics). The anterior (AC) and posterior (PC) commissures as well as the midcommissural point (MCP) were localized on a 3D MPRAGE sequence. An IRT2 coronal MRI perpendicular to AC-PC plane and centered 3 mm posterior to the MCP was then performed and the slice crossing the anterior pole of the red nucleus was retained. The target was placed at the inferolateral part of the 'subthalamic zone', defined superiorly by the thalamus, medially by the midline, inferiorly by the substantia nigra and laterally by the internal capsule. The target coordinates were calculated by the UCLF program (Radionics) according to the MCP.
Results: 52 targets were projected on sagittal, coronal and axial views of the Schaltenbrand and Wahren atlas (SWSA). Our mean target projects between the STN and the substantia nigra pars reticulata. Considering the double oblique approach and the implantation of the distal contact of the final electrode at the target or below. We expect that at least one contact will project inside the STN.
Conclusion: The procedure validation is based on the exact matching of the SWSA theoretical target and our mean target. The target distribution over the SWSA anatomical limits of the STN suggests a possible variability of STN position between individuals. The use of visual landmarks located close to the STN may be more adapted for each single patient.