An experimental study to evaluate the accuracy of diencephalic and pallidal target localization using the Brown-Roberts-Wells stereotactic system and unreformatted axial GE8800 CT scanning.

An experimental study was undertaken to evaluate the accuracy with which the intercommissural line (IL) length and anterior-posterior commissural (AC-PC) plane could be selected using unreformatted axial CT8800 imaging. Using these reference points, the Schaltenbrandt and Bailey stereotactic atlas and the Brown-Roberts-Wells (BRW) stereotactic system 1.82 mm ball bearings were deposited at selected diencephalic and pallidal targets in cadaver brains. There were errors in both IL length (median 1.5 mm) and AC-PC plane (median forward angulation of 9 degrees) estimation. Ball bearing deposition into large nuclei such as the pulvinar and globus pallidus and those in proximity to the mid IL such as the nuclei ventro oralis anterior (Voa), ventro oralis posterior (Vop) and ventro intermedius (Vim) was generally good; however, localization of the relatively small intralaminar nucleus was poor. This study suggests that when the AC and PC are not well imaged on sagittal reformations of axial diencephalic CT scans estimation of the AC-PC plane and IL from axial CT scans may be accurate enough for anatomical localization of certain functional stereotactic targets. The implications of this experimental study to operative functional stereotaxy are discussed.