Brain shift during deep brain stimulation surgery for Parkinson's disease.

Background: Brain shift may occur during deep brain stimulation (DBS) surgery, which may affect the position of subcortical structures, compromising target localization.

Methods: We retrospectively evaluated pre- and postoperative magnetic resonance imaging in 50 Parkinson's disease patients who underwent bilateral subthalamic nucleus (STN) DBS. Patients were separated into two groups: group A - those with <2 mm cortical displacement (66 leads) and group B - those with >or=2 mm cortical displacement (34 leads). Pre and post-op coordinates of anterior (AC) and posterior commissures (PC), as well as the boundaries of red nucleus (RN) were compared.

Results: AC-PC shortening due to posterior displacement of AC correlated with cortical displacement (p < 0.02) and was significantly greater in group B (0.41 +/- 0.68 mm) than A (0.04 +/- 0.76 mm; p < 0.005). Posterior shift of AC and RN's center positively correlated (p < 0.0001). Shift appeared to impact the number of microelectrode tracks made to optimize STN targeting. AC-PC shortening also correlated with age (p < 0.003) and duration of surgery (p < 0.04).

Conclusions: Subcortical structures shift during DBS surgery. This shift appears to be gravity-dependent since structures only shifted posteriorly, and patients were primarily in the supine position. Posterior shift of RN may indicate STN displacement. Such positional change may compromise target localization, requiring multiple microelectrode adjustments. This may provide indirect justification for the necessity of microelectrode recordings during DBS surgery.