STEREOTAXIC PALLIDOTOMY AND THALAMOTOMY USING INDIVIDUAL VARIATIONS OF ANATOMIC LANDMARKS FOR LOCALIZATION

OBJECTIVE: The optimal choice of imaging and localization for stereota ctic surgery for movement disorders remains uncertain, with controvers y surrounding the use of microelectrode recording and the role of dist ortion of magnetic resonance imaging (MRI) scans in reducing the accur acy of lesion placement. We review our experience with 67 pallidotomie s and 35 thalamotomies performed without microelectrode recording, usi ng instead individual variations in anatomic landmarks. METHODS: Compu ted tomography is Based as the primary modality, with comparison with carefully angled MRI scans and the use of neural structures, such as t he mamillary bodies and the vascular anatomy. Pallidal target sites ar e chosen immediately lateral and superior to the optic tract on a line bisecting the axis of the peduncle, with macrostimulation guiding the final adjustment of target position. Forty-seven patients undergoing unilateral pallidotomies were studied in the ''off'' state and the ''o n'' state using a modified Unified Rating Scale for Parkinson's diseas e (URSP) score and a dyskinesia scale, preoperatively and postoperativ ely at 2 weeks, 2 months, 6 months, and 12 months. in the 31 patients undergoing thalamotomy, tremor was rated preoperatively and postoperat ively as near-complete resolution, partial resolution, and failure. RE SULTS: The ''off'' state Unified Rating Scale for Parkinson's disease motor score declined from 42.0 to 32.2 at 2 weeks after surgery (P < 0 .0001, n = 42). The Unified Rating Scale for Parkinson's disease motor score was 34.2 at 2 months (P < 0.0001, n = 35), 29.4 at 6 months (P < 0.0001, n = 27), and 24.9 at a 2 months (P = 0.005, n = 12), represe nting an overall improvement in ''off'' state motor function of approx imately 25 to 40%. The ''on'' state dyskinesia score fell from 5.5 to 2.0 at 2 weeks (P < 0.0001) and persisted in the later visits. The dys kinesia score for the contralateral side fell from 2.5 preoperatively to 0.26 at 2 weeks, 0.28 at 2 months, 0.22 at 6 months, and 8.0 at 12 months, Of the patients undergoing thalamotomies, 65% experienced near -complete or complete tremor resolution, 23% experienced partial tremo r relief, and 13% were considered treatment failures. CONCLUSION: Ster eotactic procedures for movement disorders requiring high precision ca n be safely acid successfully performed without file use of microelect rode recording techniques. Meticulous alignment of MRI and computed to mographic scans based on visualized anatomy allows precise lesion plac ement and avoids the distortion inherent in MRI scans.