Targeting of the Subthalamic Nucleus in Patients with Parkinson's Disease Undergoing Deep Brain Stimulation Surgery

Abstract

Precise stereotactic targeting of the dorsolateral motor part of the subthalamic nucleus (STN) is paramount for maximizing clinical effectiveness and preventing side effects of deep brain stimulation (DBS) in patients with advanced Parkinson's disease. With recent developments in magnetic resonance imaging (MRI) techniques, direct targeting of the dorsolateral part of the STN is now feasible, together with visualization of the motor fibers in the nearby internal capsule. However, clinically relevant discrepancies were reported when comparing STN borders on MRI to electrophysiological STN borders during microelectrode recordings (MER). Also, one should take into account the possibility of a 3D inaccuracy of up to 2 mm of the applied stereotactic technique. Pneumocephalus and image fusion errors may further increase implantation inaccuracy. Even when implantation has been successful, suboptimal lead anchoring on the skull may cause lead migration during follow-up. Meticulous pre- and intraoperative imaging is therefore indispensable, and so is postoperative imaging when the effects of DBS deteriorate during follow-up. Thus far, most DBS centers employ MRI targeting, multichannel MER, and awake test stimulation in STN surgery, but randomized trials comparing surgery under local versus general anesthesia and additional studies comparing MER-STN borders to high-field MRI-STN may change this clinical practice. Further developments in imaging protocols and improvements in image fusion processes are needed to optimize placement of DBS leads in the dorsolateral motor part of the STN in Parkinson's disease.

Keywords: Deep brain stimulation; Magnetic resonance imaging; Microelectrode recordings; Parkinson’s disease; Subthalamic nucleus; Targeting.

Fig. 1

Coronal representation of the motor, associative, and limbic subdivisions of the human STN. A four-contact DBS lead is positioned to cover the dorsolateral motor part of the STN, at a safe distance from the limbic STN and internal capsule fibers

Fig. 2

Axial (upper) and coronal (lower) midbrain sections used for target planning during DBS of the STN on 4 different MRI sequences. On coronal 7-T T2-weighted MRI (7.0-T T2, lower right panel), the STN can be distinguished from surrounding white matter and the more ventrally located substantia nigra pars reticulata (SNr). SWI susceptibility-weighted imaging

Fig. 3

Axial (left) and coronal (right) midbrain section used for target planning during DBS of the STN on 3.0-T T2-weighted MRI, with superimposed diffusion tensor imaging (yellow) of the motor fibers in the internal capsule

Fig. 4

Intraoperative (left panel) and 1-year follow-up (right panel) analysis of DBS lead on semi-sagittal CT reconstructions parallel to the lead. Intraoperative CT shows pneumocephalus, posteriorly shifted frontal cortex, and a straight lead trajectory. Follow-up CT shows resolved pneumocephalus and anterior bending of the DBS lead

Fig. 5

Axial 1.5-T T2 of left midbrain showing typical ± 3.5 mm diameter artifact of DBS lead (left panel). Semi-sagittal T1 and CT reconstructions parallel to the lead (four panels on the right) show that the diameter of the lead artifact on MRI (3.6 mm) and CT (3.3 mm) is considerably thicker than the actual diameter of the DBS lead (1.3 mm)