Comparison of MRI and ventriculographic target acquisition for posteroventral pallidotomy

The true accuracy of MRI scanners utilized for target acquisition in functional stereotaxis remains undefined. We have performed pallidotomies at the Loma Linda University Medical Center using both MRI and MRI concomitant with positive contrast ventriculography. A retrospective study of 33 cases revealed significant differences in coordinates obtained by MRI alone and MRI concomitant with ventriculography (antero-posterior coordinates, mean error: 2.6 mm, range 0.5-6.8 mm; Z coordinates: mean error 4.6 mm, range 0-19 mm). While MRI promises excellent target identification, the generated target coordinates significantly stray from the optimal target. Ventriculography corrects the MRI coordinates and demonstrates the position of the radiofrequency probe with respect to the target and anatomic reference points.