Implantation of Deep Brain Stimulation Electrodes Under General Anesthesia for Parkinson Disease and Essential Tremor

Introduction

Deep brain stimulation (DBS) has proven to be an effective treatment for symptoms of Parkinson disease (PD), essential tremor (ET), congenital or acquired dystonias, and other movement disorders. Although not currently practiced outside of clinical trials, DBS for medically refractory psychiatric diseases, including depression, obsessive-compulsive disorder, and posttraumatic stress disorder, have been undertaken or are ongoing, and the efficacy of DBS for these is being evaluated. ^,

In the early stereotactic era, when targeting was based on ventriculographically derived coordinates, microelectrode recording (MER) techniques were employed to refine the location of stereotactic targets based on standard anatomic stereotactic atlases derived from cadaveric dissections. Intraoperative stimulation with micro- or macro-electrodes also provided additional physiological confirmation of target acquisition.

Currently, in most neurosurgical centers worldwide, DBS electrodes are placed in patients using frame-based magnetic resonance imaging (MRI) stereotaxy with adjunctive MER and physiological mapping of target structures, including intraoperative motor testing. These procedures are performed with the patient awake, using local anesthesia combined with light sedation, which allows motor testing, and determination of “off-target” effects of therapeutic levels of stimulation. While MER mapping likely entails additional risk of intraparenchymal hemorrhage and permanent neurologic deficit, its value to the patient outcomes from DBS procedures has not been established. Furthermore, what constitutes “MER mapping” varies substantially between institutions, such that a uniform risk may be difficult to determine.

The use of MER guidance for electrodes presumes that physiologically defined targeting will produce improvements in the subsequent clinical outcome. In fact, it has been stated that MER mapping is required due to “the impossibility to date of alternative methods to directly target the sensorimotor regions … of the DBS targets.” Image-guided implantation of DBS electrodes, on the other hand, assumes that anatomically defined targeting is sufficient to produce outcomes of the same quality as MER-guided procedures. The additional cost of MER during electrode implantation in the subthalamic nucleus (STN) is significant, and can double or triple the cost of DBS treatment. In the absence of strong evidence supporting the use of MER, and in light of the potential risks and costs of employing this technique, one must consider the question of whether an alternate technique that avoids such risks and costs should be preferred ( Fig. 105.1 ).

If, in fact, MER mapping could be avoided, potentially better outcomes from DBS implantation could be reasonably expected. High-field (3T) MRI now allows direct visualization of target centers, and multiple modalities of intraoperative imaging provide visual confirmation of electrode location in relation to target structures. The accuracy of DBS electrode placement using image guidance has been well established with intraoperative MRI (iMRI) ^, and intraoperative CT (iCT). ^,

In this chapter, we present the case that asleep DBS (aDBS) using preoperative 3T MRI imaging and iCT confirmation of electrode placement represents a safe, accurate, and effective alternative for routine implantation of DBS electrodes.

Awake Versus Asleep Deep Brain Stimulation implantation

There are now a large number of studies examining the results of aDBS implantation. The asleep technique relies completely on image guidance, by either direct visualization of the target and electrode using iMRI, or the fusion of iCT imaging with preoperative MRI. The former allows, to a certain extent, the prediction of electrode track prior to placement of the DBS lead, while the latter relies on a post hoc evaluation of lead position in comparison with planned operative trajectory. For the STN and globus pallidus internus (GPi), direct targeting is employed, while for Vim, traditional AC-PC based targeting is used. The advent of intraoperative imaging allows the assessment of actual electrode position relative to its intended target ( Fig. 105.2 ).

Safety of Asleep Deep Brain Stimulation

The safety of aDBS implantation has been evaluated explicitly in an increasing range of studies. Burchiel reviewed 119 electrode implantations in 60 consecutive patients implanted during asleep procedures. In this series, there were no reported intraparenchymal hemorrhages, no new neurological deficits or deaths. Sharma examined 20 patients undergoing implantation of 28 leads, and reported no hemorrhages and 1 patient with temporary swallowing difficulty after unilateral GPi lead placement. aDBS was used to implant 35 consecutive patients at GPi for PD in a study by Mirzadeh and colleagues, with outcomes evaluated in a prospective fashion. There were no perioperative complications noted during this study.

From a safety standpoint, there are a few direct comparisons of asleep versus awake DBS implantation. In a comparison of asleep versus awake DBS for ET, Chen and colleagues reported no intraoperative complications in 60 leads placed using awake techniques and 29 leads placed in asleep patients. Neither cohort experienced any perioperative complications. In another study, 53 electrodes (29 patients) were implanted asleep using intraoperative MR guidance. There were no reported hemorrhages, two infections, and one poorly placed electrode requiring revision; reference was made to a historical cohort of 76 electrodes implanted using MR guidance in addition to MER, which included two intraparenchymal hemorrhages, no infections, and one misplaced electrode. These differences are not statistically significant, and conclusions regarding outcome differences must take into consideration small sample size and the often retrospective nature of these reports.

Data do exist that support the conclusion that MER does increase hemorrhage risk during awake DBS implantation. In a recent review, Fenoy and colleagues found that during 1333 lead implantations using MER, the intraparenchymal hemorrhage rate is 5.0%. In contrast, in a large series of image-guided DBS implantations without MER, the hemorrhage rate across 417 electrode implantations was reduced approximately fivefold, to 0.9%. That MER appears to be associated with a significant increase in hemorrhage rate is consistent with an extensive review of literature examining lesioning and stimulation surgeries, which demonstrated an approximately fivefold increase in hemorrhage rate when MER is employed during stereotactic surgery. Thus, in considering the safety profile of aDBS without MER, one must take into account the fact that this technique generally decreases the number of brain penetrations, consistent with a reduction in the risk of intraparenchymal hemorrhage.