Comparison of anatomic and neurophysiological methods for subthalamic nucleus targeting

OBJECTIVE: The subthalamic nucleus (STN) has recently become the surgical t arget of choice for the treatment of medically refractory idiopathic Parkin son's disease. A number of anatomic and physiological targeting methods hav e been used to localize the STN. We retrospectively reviewed the various an atomic targeting methods and compared them with the final physiological tar get in 15 patients who underwent simultaneous bilateral STN implantation of deep brain stimulators. METHODS: The x, y, and z coordinates of our localizing techniques were anal yzed for 30 STN targets. Our final targets, as determined by single-cell mi croelectrode recording, were compared with the following: 1) targets select ed on coronal magnetic resonance inversion recovery and T2-weighted imaging sequences, 2) the center of the STN on a digitized scaled Schaltenbrand-Wa hren stereotactic atlas, 3) targeting based on a point 13 mm lateral, 4 mm posterior, and 5 mm inferior to the midcommissural point, and 4) a composit e target based on the above methods. RESULTS: All anatomic methods yielded targets that were statistically signi ficantly different (P < 0.001) from the final physiological targets. The av erage distance error between the final physiological targets and the magnet ic resonance imaging-derived targets was 2.6 +/- 1.3 mm (mean +/- standard deviation), 1.7 +/- 1.1 mm for the atlas-based method, 1.5 +/- 0.8 mm for t he indirect midcommissural method, and 1.3 +/- 1.1 mm for the composite met hod. Once the final microelectrode-refined target was determined on the fir st side, the final target for the contralateral side was 1.3 + 1.2 mm away from its mirror image. CONCLUSION: Although all anatomic targeting methods provide accurate STN lo calization, a combination of the three methods offers the best correlation with the final physiological target. In our experience, direct magnetic res onance targeting was the least accurate method.