Direct visualization of the human subthalamic nucleus with 3T MR imaging

Electrical stimulation of the subthalamic nucleus (STN) is an accepted treatment for advanced Parkinson disease (PD). Although procedural details are well established, targeting STN remains problematic because of its variable location and relatively small size (20-30 mm(3)). A combination of anatomic imaging with a stereotactic frame, atlas coordinates, and intraoperative neurophysiology is currently considered the most reliable approach for STN targeting. CT imaging is dependent on atlas coordinates, because the STN is not visualized. The STN is also difficult to visualize directly by using MR imaging at 1.5 T.

We performed preoperative stereotactic MR imaging at 3T to visualize the STN in 13 patients undergoing deep-brain stimulation for PD. With the patient positioned within a standard Leksell type G stereotactic frame localizer, rapidly acquired scout images are used to prescribe volumes of contiguous high-resolution T2-weighted fast spin-echo images in the axial, sagittal, and coronal planes through the midbrain and basal ganglia. The STN is identified in all 3 planes by cross-referencing in a 3-plane viewer. These coordinates are used for surgical targeting.

At 3T, the STN was visualized as a small, hypointense, almond-shaped structure in 3 planes located immediately lateral to the anterior edge of the red nucleus, medial to the internal capsule, about 5 mm inferior, 1-2 mm posterior, and 9-12 mm lateral to the midcommissural point. Intraoperative microelectrode recordings confirmed these coordinates in all cases from the first microelectrode pass, thereby eliminating prolonged intraoperative electrophysiological STN searching and tissue disruption that may occur from multiple passes.

3T MR imaging appears to be an excellent tool for reliable and accurate direct visualization of the human STN, necessary for precise surgical targeting.