Imaging Advances Promote Growth of DBS
by Warren Grill, senior technical editor
One of the primary challenges to continued successful growth of deep brain stimulation is the complexity of the surgical implant procedure. The anatomical targets are small and difficult to visualize, and when the burr hole is made through the skull, the brain moves.
Microelectrode recording is used at most centers to refine the location of stimulation targets, but increased numbers of microelectrode tracks are associated with an increased risk for intracranial hemorrhage. Two recent publications in the journal Neurosurgery present advances in magnetic resonance imaging and surgical techniques that could improve outcomes in patients with deep brain stimulation.
Geoffrey Young and colleagues developed a modified T1-weighted MRI method to enhance visualization of brain targets for preoperative planning. This method eliminates the need for an additional T2-weighted scan, thereby reducing imaging time and cost, as well as the potential errors of registering the two different scans. The method enabled visualization of the subthalamic nucleus, substantia nigra pars reticulata, red nucleus, and the ventral intermediate nucleus of the thalamus, with contrast superior to that achieved with T2 weighted scans.
Although not demonstrated in the study by Young et al., the improved visualization of DBS targets is expected to improve the accuracy of electrode implantation. This advance may reduce the number of microelectrode passes required for accurate targeting, and this will reduce the associated risk for intracranial hemorrhage, as well as the duration of the surgical procedure. Finally, these enhancements may enable more reliable post-implant studies to correlate electrode location with clinical efficacy, and such studies will contribute to refining the location of the optimal anatomical targets for DBS.
In a second study, Igor Maldonado and colleagues from Phillippe Coubes’ group in Montpellier, France, report their outcomes of DBS electrode implantation. Targeting was guided exclusively by preoperative imaging, and implantation was conducted under general anesthesia with a single penetration with the clinical electrode and no microelectrode recording. The team implanted 478 electrodes in 220 procedures in 194 patients with no evidence of perioperative intracranial hemorrhage, whereas other studies routinely report hemorrhage rates of 2 to 4 percent. However, there was one hemorrhage several days after surgery in a patient with Parkinson’s disease.
It is not clear how well these results will generalize, as the vast majority of patients in the study were being treated for dystonic-diskinetic syndromes, and only 52 electrodes were implanted for Parkinson’s disease, by far the most common indication for DBS. Further, the cohort had an average age of only 31, whereas most recipients of DBS are substantially older, and age may contribute to an increased risk of hemorrhage. As well, there was no report of efficacy, and it is not clear whether functional outcomes with the proposed surgical approach are comparable to outcomes achieved when electrode implantation is guided by microelectrode recording and intraoperative test stimulation in awake patients.
In addition to enhancing the potential efficacy of DBS, by improving the accuracy of electrode implantation, and increasing the safety of the procedure, by minimizing the need for microelectrode recording, advanced imaging techniques may also enable more surgeons to conduct deep brain stimulation surgery.