Correlation between MRI-based stereotactic thalamic deep brain stimulation electrode placement, macroelectrode stimulation and clinical response to tremor control.

In this study we compared the position of the electronically active contact of the thalamic (Vim) deep brain stimulation (DBS) electrode to the stereotactic location of its tip. Fifteen patients with either Parkinson's disease (PD) or essential tremor (ET) underwent stereotactic, MRI-based placement of the Medtronic quadripolar DBS electrode. An overall improvement of 69% was achieved in the tremor scores during a period of 1-13 months after implantation of the DBS electrode. Eleven patients with ET showed 70% clinical improvement of tremor, compared to a 58% response observed in the 4 patients with PD. The electrode tip center was 11.2 +/- 1.54 mm lateral to the third ventricular wall, 5.38 +/- 1.02 mm anterior to the posterior commissure and 2.9 +/- 3.57 mm inferior to the level of AC-PC line. The most significant deviation from the planned stereotactic target was observed in the Z-coordinate. In our group of patients, stimulation settings favored the contacts closer to the AC-PC line, correcting the electrode tip position to 0.80 +/- 2.84 mm (p < 0.001) inferior to the level of the AC-PC line. In our experience, thalamic DBS offers a reversible and adjustable 'lesion' to compensate for the anatomic variabilities encountered in the positioning of the DBS electrode tip.