An Analysis of the Use of Multichannel Microelectrode Recording During Deep Brain Stimulation Surgeries at a Single Center

An Analysis of the Use of Multichannel Microelectrode Recording During Deep Brain Stimulation... Abstract BACKGROUND Microelectrode recording (MER) can be used to map out the target nucleus and identify ideal lead placement. OBJECTIVE To assess the use of multichannel MER to increase the efficiency of lead placement without compromising patient safety. METHODS Analysis of a single center's technique for utilizing multichannel MER with 3 consistent anterior-to-posterior simultaneous passes that include an evaluation of the location of final lead placement, patient diagnosis, target nuclei, and additional work involved for refinement of targeting. Lead revision rates and rate of hemorrhage are also assessed. RESULTS There were a total of 237 lead placements in 123 patients over a 4-yr period. In 4.2% of lead placements, additional planning was required, while only 2.5% required additional MER. The lead placement matched 51.3% of the time in bilateral placements and was consistent regardless of target nuclei. In 84.8% of cases, the final lead placement was within the initial 3 MER passes. An additional 11.3% could be placed without the need for an additional pass. There were 2 lead revisions and no hemorrhage or stroke complications. CONCLUSION This series demonstrates that our technique of multichannel MER leads to accurate and efficient lead placement maintaining its safety profile. Deep brain stimulation, Microelectrode recording, Movement disorders, Parkinson disease, Subthalamic nucleus, Tremor ABBREVIATIONS ABBREVIATIONS CSF cerebrospinal fluid CT com-puted tomography DBS deep brain stimulation GPi internal globus pallidus MER microelectrode recording MRI magnetic resonance imaging OR operating room STN subthalamic nucleus ViN ventral intermediate nucleus Deep brain stimulation (DBS) delivers benefit to those with treatment-resistant movement disorders.1,2 The US Food and Drug Administration has approved 3 indications for DBS since its inception. These treatments are for essential tremor, approved in 1997; Parkinson disease, approved in 2002; and dystonia, approved in 2003. It is well tolerated and has become the most common neurosurgical procedure for movement disorders. Because DBS is an elective procedure, it is imperative to maintain a low complication rate and maintain accuracy and efficiency in the placement of electrodes. The accuracy of electrode placement has been studied by the use of intraoperative imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT),3,4 as well as the continued use of microelectrode recording (MER).2,5-10 MER can be used to map out the target nucleus and define the best location for lead placement. The literature has supported the use of MER given the additional data that it obtains.2,5-10 Some reviews have suggested that using MER in DBS can lead to an increased occurrence of hemorrhage, especially with multiple passes during surgery,10,11 but other reviews have not observed this trend.12,13 The additional data that are obtained by MER in order to accurately place the electrode outweighs the risks of hemorrhage when it is kept significantly low.14,15 There has been an interest in multichannel MER. Potential benefits include more information to define the target nucleus and decreased intraoperative time devoted to MER, leading to a more accurate and efficient placement of the electrode. Several studies have demonstrated that, on average, multiple MER passes are required and several may be needed for accurate placement of the electrode.7,10,16-18 Multichannel MER is therefore useful for target refinement and may limit the need for additional passes to be performed.19,20 The central target track that was determined during preoperative stereotactic planning and track that demonstrated the best recording of signals do not always equate to the final lead placement, which further demonstrates the utility of multichannel MER.21 It has also been demonstrated that there is no difference in the number of MER passes that are required based on target nucleus, demonstrating the importance of MER and multichannel MER in all targets.22 This is a large, retrospective review series that evaluated a single center's approach to utilizing multichannel MER to define the target nucleus. It included an evaluation of the location of final lead placement compared to initial targeting, as well as additional work involved for refinement of targeting when utilizing a multichannel approach. An analysis of final lead placement comparing both sides in bilateral placement and a comparison of different targets was also performed. Lead revision rates and rate of hemorrhage was also assessed. These factors can be used to define the importance of multichannel MER, as well as its efficiency and safety. METHODS This study is a retrospective analysis of 123 patients who underwent initial DBS surgery in a single institution from 2012 to 2015 performed by a single surgeon. Diagnoses of these patients included Parkinson's disease, essential tremor, and dystonia. Patients ranged from 27 to 85 yr of age. There were a total of 237 lead placements, with 113 bilateral cases, in which one of the cases had 3 leads placed, as well as 10 unilateral cases. Data for the study was incorporated via a retrospective chart review of a prospective data management report. All patients undergoing an initial implant were included in the analysis, with follow-up ranging from 6 mo to 4 yr. IRB approval was not necessary given this was a retrospective analysis of a prospective database without patient identifiers. This was determined by the local IRB board and ethics committee. The analysis included an evaluation of technique utilizing 3 simultaneous MER passes in order to identify the optimal target for lead location. This analysis included target nuclei, patient diagnosis, final lead placement, and whether additional lead passes were needed. Further analysis and evaluation of additional steps was performed for all cases in which additional planning was necessary during the surgery beyond the 3 simultaneous tracks. Evaluation of lead revision and intracranial hemorrhage was also determined. Surgical Technique Patients underwent Leksell head frame (Elekta, Sweden) placement just prior to the procedure. A CT scan was obtained and merged with an MRI, which was obtained approximately 1 wk prior to the procedure. Targets were chosen preoperatively using Framelink software for initial coordinates. The surgeon would adjust the preprogrammed coordinates based on factors such as brain atrophy, size of lateral and third ventricles, and angles chosen for entry based on avoidance of key structures and blood vessels. Utilizing contrast on the preoperative MRI in order to identify blood vessels within the course of the electrodes further assisted this approach.15,22 The patient was positioned in a head-elevated supine position utilizing the Mayfield head holder adapter for the frame. Linear cranial incisions were utilized for the burr hole. The dura was incised in a cruciate fashion, with the free edges brought back with the bipolar electrocautery, followed by using the bipolar to make a small pial opening. Each track was tested to ensure the cannula was passed freely into the burr hole; then, Tisseel Fibrin Sealant (Baxter International; Deerfield, Illinois) was placed into the burr hole to limit cerebrospinal fluid (CSF) leak and potential pneumocephalus. The electrodes were placed using awake MER, with macrostimulation through the MER electrode done to identify the optimal location for final lead placement. MER was performed using 3 simultaneous passes placed 2 mm apart in an anterior-to-posterior projection with the FHC drive with the presumed planned target as the central track. We did not determine borders of our specific target nucleus, but rather determined positioning based on a strong MER, efficacy with intraoperative patient testing, and none to limited side effects based on the therapeutic window. If the amplitudes and strength of the MER were not ideal, we may have chosen to perform motor testing during the planned track to identify active cells, have a potential map of the homunculus, and attempt to increase amplitudes for improved signals. Based on the information gathered with these 3 initial passes, as well as the macrostimulation for side effect profile and efficacy, a determination would be made on lead placement and whether an additional MER and/or macrostimulation track was necessary. In cases in which the target was not determined to be within the 3 MER tracks, a decision would be made on whether the final lead placement could be 2 mm medial or lateral without additional testing, or whether additional information would need to be gathered. The decision to proceed with placement of the lead in a medial or lateral track without additional testing would be based on a treatment response that occurred within a very narrow therapeutic window. Although the Z-axis may have been adjusted slightly during the initial preoperative planning based on the AC-PC line, the final depth was determined from the MER. Intraoperative fluoroscopy was used to further confirm placement and positioning. Strict blood pressure control is maintained during the procedure with mean arterial pressures held below 80 mm Hg until completion of the procedure, when patients would be allowed to slowly normalize in the recovery area. A postoperative head CT was obtained within 3 h of the procedure, along with a brain MRI the morning following the procedure prior to discharge.15,22 One week after this surgery, the extension lead was connected, and the IPG was implanted under general anesthesia. RESULTS The demographic information for the patients is shown in Table 1. There were 237 lead placements in 123 patients in this study. The mean patient age was 66.4 with a range from 27 to 85. Ten, or 4.2%, of these lead placements required additional planning. The details of this additional planning are shown in Table 2. Six of these 10 placements, or 2.5% of all placements, required additional MER. One additional patient had 3 leads placed during the surgery due to a diagnosis of both Parkinson disease and essential tremor, with bilateral subthalamic nucleus (STN) leads and 1 ventral intermediate nucleus (ViN) lead. This decision was made intraoperatively given complete lack of unilateral tremor control with placement in STN. The procedures for the remainder of the patients requiring additional testing were performed by placing the MER electrode using only macrostimulation. The most common diagnosis was Parkinson disease, and the most common target was the subthalamic nucleus. In those patients not requiring additional work, a decision could be made on placement within the 5 tracks of the FHC drive based on the MER, and macrostimulation for side effect profile and efficacy. TABLE 1. The Table Provides Demographic Information on the Surgical Patients Included in the Study Number of patients: 123 with 237 lead placements  Placements that required additional passes: 10  Mean age: 66.4  Range of ages: 27-85  Diagnoses:    81 Parkinson's disease      61 STN      16 ViM      4 GPi    39 essential tremor      39 ViM    3 dystonia      3 GPi  Number of patients: 123 with 237 lead placements  Placements that required additional passes: 10  Mean age: 66.4  Range of ages: 27-85  Diagnoses:    81 Parkinson's disease      61 STN      16 ViM      4 GPi    39 essential tremor      39 ViM    3 dystonia      3 GPi  View Large TABLE 2. Analysis of Special Placements. The Table Provides Additional Information on the Cases That Involved Extra Steps in the Typical Lead Placement Procedure Patient  Side  Target  Diagnosis  Notes  1  Left  ViM  ET  Performed additional tract 2 mm lateral with MER but placed at target  2  Bilateral  STN  PD  Performed additional macrostimulation tract on left side 2 mm medial without MER and placed in this location  3  Right  ViM  ET  Performed macrostimulation and placed lead 2 mm lateral without MER on lateral tract  4  Bilateral  GPi  Dystonia  Placed 2 mm medial to target on right side without additional tract but performed 2 single MER passes secondary to concern of vasculature  5  Bilateral  STN  PD  Performed additional tract medially on left with MER and placed 4 mm medial to target  6  Bilateral  STN  PD  Performed additional tract laterally on left with MER, but placed 2 mm anterior  7  Bilateral  STN  PD  Performed 2 additional macrostimulation testing tracts medial and anterior/medial on left without MER and placed anterior/medial  8  Bilateral  ViM  ET  Performed 2 additional tracts lateral and posterior/lateral with MER and placed posterior/lateral  9  Bilateral  ViM  ET  Performed additional tract on left laterally with MER and placed laterally  10  Bilateral  STN  PD  Performed additional macrostimulation tract laterally without MER on right and placed at target  Patient  Side  Target  Diagnosis  Notes  1  Left  ViM  ET  Performed additional tract 2 mm lateral with MER but placed at target  2  Bilateral  STN  PD  Performed additional macrostimulation tract on left side 2 mm medial without MER and placed in this location  3  Right  ViM  ET  Performed macrostimulation and placed lead 2 mm lateral without MER on lateral tract  4  Bilateral  GPi  Dystonia  Placed 2 mm medial to target on right side without additional tract but performed 2 single MER passes secondary to concern of vasculature  5  Bilateral  STN  PD  Performed additional tract medially on left with MER and placed 4 mm medial to target  6  Bilateral  STN  PD  Performed additional tract laterally on left with MER, but placed 2 mm anterior  7  Bilateral  STN  PD  Performed 2 additional macrostimulation testing tracts medial and anterior/medial on left without MER and placed anterior/medial  8  Bilateral  ViM  ET  Performed 2 additional tracts lateral and posterior/lateral with MER and placed posterior/lateral  9  Bilateral  ViM  ET  Performed additional tract on left laterally with MER and placed laterally  10  Bilateral  STN  PD  Performed additional macrostimulation tract laterally without MER on right and placed at target  View Large There were 113 bilateral cases, as shown in Figure 1. Fifty-eight of those cases, or 51.3%, had lead placements that matched bilaterally. This analysis continues based on which nucleus was targeted for the procedure. The subthalamic nucleus cases matched 31 out of 59 times, or 52.5%. The ventral intermediate nucleus cases matched 24 out of 47 times, or 51.1%. The internal globus pallidus (GPi) cases matched 3 out of 7 times, or 42.9%. These findings show little difference in bilateral matching based on the target. Only approximately half of all the bilateral placements matched on both sides, demonstrating the need for performing MER on both sides. FIGURE 1. View largeDownload slide The bar graph displays the percent of cases that were bilateral, and the final placement matched on both sides. This graph is based on the target nucleus of the placement. FIGURE 1. View largeDownload slide The bar graph displays the percent of cases that were bilateral, and the final placement matched on both sides. This graph is based on the target nucleus of the placement. The placements of the final lead in relation to the target on the X/Y axis are displayed numerically in Table 3 and graphically in Figure 2. Out of the 237 total placements, 106 were at target, 54 were posterior, 41 were anterior, 24 were medial, 3 were lateral, and 8 qualified as other. Other would include a final track that is not fixed in the 5-track FHC drive, such as a diagonal track compared to central. These values equate to 44.7% at target, 22.8% posterior, 17.3% anterior, 10.1% medial, 1.3% lateral, and 3.4% other. In 84.8% of cases, the final lead placement was either at target, anterior, or posterior, and therefore within the initial 3 MER passes. An additional 11.3% was covered medially or laterally without the need for an additional pass based on the data gathered. Table 4 shows the final placements in relation to target on the Z-axis. The data show that 113 were at target, while 32 were above and 92 were below. These values equate to 47.7% at target, 13.5% above, and 38.8 below. The average depth away from target was 0.27 mm below. FIGURE 2. View largeDownload slide The pie chart displays the location of final lead placements in relation to the targeted nucleus. FIGURE 2. View largeDownload slide The pie chart displays the location of final lead placements in relation to the targeted nucleus. TABLE 3. The Table Displays the Direction of Final Lead Placement Based on the Initial Microelectrode Recording for Each Target Nucleus on the X/Y-axis   Anterior  Posterior  Medial  Lateral  At target  Other  Total  STN  31  14  18  1  54  2  120  ViM  6  37  4  3  48  5  103  GPi  4  3  2  0  4  1  14  Total  41  54  24  4  106  8  237    Anterior  Posterior  Medial  Lateral  At target  Other  Total  STN  31  14  18  1  54  2  120  ViM  6  37  4  3  48  5  103  GPi  4  3  2  0  4  1  14  Total  41  54  24  4  106  8  237  View Large TABLE 4. The Table Displays the Direction of Final Lead Placement Based on the Initial Microelectrode Recording for Each Target Nucleus on the Z-axis   Above  Below  At target  Total  STN  6  74  40  120  ViM  24  17  62  103  GPi  2  1  11  14  Total  32  92  113  237    Above  Below  At target  Total  STN  6  74  40  120  ViM  24  17  62  103  GPi  2  1  11  14  Total  32  92  113  237  View Large This same analysis for final lead location was further based on the target nuclei. This is shown in Figure 3. Fifty-two out of 115 subthalamic nucleus cases were at target. Forty-nine out of 99 ventral intermediate nucleus cases were at target. Four out of 13 internal globus pallidus cases were at target. These findings show that the final lead placement is not consistently at target and is irrespective of the target nuclei. FIGURE 3. View largeDownload slide The bar graph displays the final lead placement based on the target nucleus. FIGURE 3. View largeDownload slide The bar graph displays the final lead placement based on the target nucleus. An analysis was also performed looking at the length of the surgery from first incision until dressing and is shown in Figure 4. The results show a small peak in low numbers due to the unilateral cases and a small peak in higher numbers due to early cases with this technique. Over the study period, there was a decrease in surgery time, demonstrating improvement in the described technique with procedure refinement and increasing experience of the implanting surgeon. This decrease in procedure time became more consistent, although there would be some variation in operating room (OR) time based on additional passes, patient cooperation, and degree of intraoperative testing necessary. Bilateral procedures, as expected, were longer than unilateral procedures. The mean and median times for bilateral procedures were 157 and 147 min, while the mean and median times for unilateral procedures were 88 and 75 min. FIGURE 4. View largeDownload slide The histogram displays the operative times of the surgeries included in this study. FIGURE 4. View largeDownload slide The histogram displays the operative times of the surgeries included in this study. In the follow-up period for all patients, ranging from 6 mo to 4 yr, there was a total of 2 lead revisions. Both of these revisions were required due to loss of efficacy over time. Both were ViM lead placements for essential tremor and required being moved 2 mm lateral from their placed position. There were no hemorrhage or stroke complications in our series. DISCUSSION DBS is a commonly utilized neurosurgical intervention that is an elective procedure. Surgical technique is imperative to its success. Multiple factors are involved in maintaining good patient outcomes, which can include low complication rates, an efficient and safe surgery, as well and precise targeting of the desired nucleus. MER is utilized to identify the optimal location for final DBS lead placement, with studies verifying its safety and effectiveness.2,5-10,23 Multichannel MER can also be useful for target refinement.19,20 Our series evaluated the use of multichannel MER in refining surgical technique to better define the target nucleus and make the procedure more efficient while maintaining its safety profile. Its utility is in accurate lead placement with a low lead revision rate. The technique utilized incorporated 3 MER leads passed simultaneously in order to define the target nucleus. The 3 tracks include the targeted central track and additional anterior and posterior tracks. Out of the 237 leads placed in this study, only 10 required additional planning or work beyond the data recorded on the initial pass. This additional work included either utilizing an additional MER pass with macrostimulation or using a separate pass with the MER electrode for test stimulation only. Of those 10 procedures, only 6 required additional MER, which equates to 2.5%. This is in comparison with the published literature stating an average number of MER passes of 2.6,7 demonstrating the efficiency in this method as well as decreased passes of electrodes in the brain. Final Lead Placements There were 113 bilateral cases, with 51.3% having lead placements that matched on each side. This was also consistent across the different targets of STN, ViM, and GPi. These findings highlight the importance of utilizing MER on both sides to define the target nucleus, as the final track chosen only correlates in half of the procedures. This result demonstrates the need for performing MER on both sides, as leads may be most adequately placed in asymmetric positions. This may be a result of CSF loss or pneumocephalus during the opening of the dura. Analysis of final lead placement in relation to target demonstrated that 44.7% were at target, 22.8% posterior, 17.3% anterior, 10.1% medial, 1.3% lateral, and 3.4% in a track not defined in the standard 5-track pattern of the FHC drive. The technique utilized 3 simultaneous tracks from anterior to posterior. The final lead placement was in one of these 3 tracks in 84.8% of cases. An additional 11.3% were covered medially or laterally without the need for an additional pass. This demonstrates that the majority of final lead placements will fall within the 3 tracks from anterior to posterior, and that the information gathered from these tracks will allow for the placement of the final lead without additional work in another track. In this analysis, anterior and posterior were close to equal and more common than medial or lateral, demonstrating that 3 tracks anterior to posterior is the best option for multichannel MER. The 2-mm spacing of the tracks defined in the 5-track pattern of the FHC drive is also adequate for the majority of lead placements given that average target adjustments with single-channel MER has been reported as 1 to 4 mm.10 The final lead placement was only at the target track in 44.7% of cases. This was consistent across the different targets of STN, ViM, and GPi. This demonstrates that the target nuclei do not affect the accuracy of the initial lead placement, there is utility in MER regardless of target nuclei, and that the method of three simultaneous MER tracks is a desirable technique for optimal lead location and efficiency. This is consistent with the literature demonstrating no difference in the average amount of MER passes performed to define the target based on location,22 as well as the need for multiple passes to define the target. This has been reported around an average number of MER passes of 2.6,7 as well as a modification of electrode position in 17% to 87% of cases based on the information of one single-channel MER pass.10 Utilization of this method of multichannel MER will reduce the additional passes that are commonly needed in single-channel MER cases. Operative Safety and Efficiency The median time for a bilateral procedure was just under 2.5 h, with the majority of cases between 1.5 and 3 h. With increased experience of the surgeon and refined technique, the procedure time improved from the initial cases. There is the expected variation in OR time based on additional passes, patient cooperation, and degree of intraoperative testing of the patient. These times demonstrate an efficient procedure for those utilizing MER. This is especially true when considering that our final lead placement was frequent in a different track than the one targeted. This fact held true for the contralateral side as well. There is, however, the limitation of applying our observed OR times due to factors such as other surgeons’ skill, experience, and OR setup. Lead revision was only seen in 2 patients (0.8%) over the observed follow-up period. Both were for loss of efficacy over time and both had ViM targets that were revised to a more lateral position. This lead revision rate is quite low when compared to the literature, which has reported rates varying from 2.0% to 5.7% in several reviews,14,15,22,24 but may be as high as 15.2% for lead revision, with a suspected 48.5% of these from improper targeting as seen in a more recent manuscript looking at North American databases.25 These previous findings demonstrate the accurate placement of the leads utilizing this technique with multichannel MER. There is, however, a limitation of this review, as the results of the patients for efficacy of their system was not quantified and followed. In addition, comparison of placements with or without MER would also need to be evaluated against this technique. The most serious complication of DBS is intracerebral hemorrhage. The literature shows that the incidence of intracerebral hemorrhages from stereotactic surgery, which includes ablation, is between 1% and 5%.1,26,27 The incidence of this complication in DBS procedures is low, at 0.7% to 3.9% per lead passage, and the permanent morbidity of the patient is 0% to 0.8%.2,9,12,13,28-30 Some previous studies have suggested that using MER in DBS can lead to an increased occurrence of hemorrhage, especially with multiple passes,10,11 but this finding is inconsistent with other reviews.12,13 There were no hemorrhage or stroke complications in our series, suggesting no increased risk to the patient with simultaneously passing 3 leads. The procedure includes strict blood pressure monitoring intraoperatively to maintain the mean arterial pressure at or below 80 mm Hg. It also includes vigilant preoperative planning of the proposed trajectory to avoid all potential vessels that could be in the field. The authors postulate that using 3 simultaneous MER tracks should not increase the hemorrhage rate, as it creates an anchoring of the brain as it traverses the tissue. This method may actually decrease the hemorrhage rate that has been previously observed with MER, but one can also hypothesize that the observed rate of 0% could be secondary to the number of cases performed and that as time progresses with an increase in sample size this will not hold true. Based on these factors, this technique is at least as safe as other standards, but a larger series would be needed to determine if this method is superior to others. Some have looked at the role of intraoperative imaging for improved accuracy and time efficiency in the OR,3,4 but this may not be feasible for all centers with limited intraoperative capabilities for imaging modalities such as MRI or CT. Overall, it can be determined that our technique utilizing multichannel MER with 3 simultaneous tracks running anterior to posterior can lead to time savings and efficiency in the OR, accurate lead placement, and no increased risk of intracerebral hemorrhage or stroke. CONCLUSION Our technique utilizing multichannel MER with 3 simultaneous tracks running anterior to posterior can lead to accurate lead placement, efficiency in the OR, and no increased risk of intracerebral hemorrhage or stroke. The findings highlight the importance of utilizing MER regardless of target nuclei, as well as in bilateral procedures. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Videnovic A, Metman LV. Deep brain stimulation for Parkinson's disease: prevelance of adverse events and need for standardized reporting. Mov Disord.  2008; 23( 3): 343- 349. 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An evaluation of hardware and surgical complications with deep brain stimulation based on diagnosis and lead location. Stereotact Funct Neurosurg.  2012; 90( 3): 173- 180. Google Scholar CrossRef Search ADS PubMed  23. Zeiler FA, Wilkinson M, Krcek JP. Subthalamic nucleus deep brain stimulation: an invaluable role for MER. Can J Neurol Sci.  2013; 40( 4): 572- 575. Google Scholar CrossRef Search ADS PubMed  24. Baizabal Carvallo JF, Mostile G, Almaguer M, Davidson A, Simpson R, Jankovic J. Deep brain stimulation hardware complications in patients with movement disorders: risk factors and clinical correlations. Stereotact Funct Neurosurg.  2012; 90( 5): 300- 306. Google Scholar CrossRef Search ADS PubMed  25. Rolston JD, Englot DJ, Starr PA, Larson PS. An unexpectedly high rate of revisions and removals in deep brain stimulation surgery: Analysis of multiple databases. Parkinsonism Relat Disord.  2016; 33: 72- 77. doi:10.1016/j.parkreldis.2016.09.014. Google Scholar CrossRef Search ADS PubMed  26. Levy RM, Lamb S, Adams JE. Treatment of chronic pain by deep brain stimulation: long term follow-up and review of the literature. Neurosurgery.  1987; 21( 6): 885- 893. Google Scholar CrossRef Search ADS PubMed  27. Starr PA, Turner RS, Rau G et al.   Microelectrode-guided implantation of deep brain stimulators into the globus pallidus internus for dystonia: techniques, electrode locations, and outcomes. J Neurosurg.  2006; 104( 4): 488- 501. Google Scholar CrossRef Search ADS PubMed  28. Lyons KE, Wilkinson SB, Overman J, Pahwa R. Surgical and hardware complications of subthalamic stimulation: a series of 160 procedures. Neurology.  2004; 63( 4): 612- 616. Google Scholar CrossRef Search ADS PubMed  29. Kleiner-Fishman G, Herzog J, Fisman DN et al.   Subthalamic nucleus deep brain stimulation: summary and meta-analysis of outcomes. Mov Disord.  2006; 21( suppl 14): S290- S304. Google Scholar CrossRef Search ADS PubMed  30. Terao T, Takahashi H, Yokochi F, Taniguchi M, Okiyama R, Hamada I. Hemorrhagic complication of stereotactic surgery in patients with movement disorders. J Neurosurg.  2003; 98( 6): 1241- 1246. Google Scholar CrossRef Search ADS PubMed  COMMENT The authors offer an analysis of their technique for microelectrode recording (MER) as an adjunct for accurate placement of deep brain stimulating (DBS) leads. They retrospectively analyzed 123 patients who had 237 lead placements in the subthalamic nucleus (STN), ventral intermediate nucleus (ViM), and globus pallidus (GPi). They used a standard procedure for implanting DBS leads while utilizing an MER technique with 3 electrodes in an anterior to posterior array: the central electrode in the originally planned tract and the other electrodes running 2 mm anterior and posterior. The authors looked at the risk of additional recording tracts–specifically of hemorrhage–versus the value of the data obtained from those additional MER tracts. They posit that this is particularly important given that often several MER tracts are required to appropriately place a lead. Their analysis showed that approximately 50% of bilateral leads (52.5% of STN, 51.1% of ViM, and 42.9% of GPi) were symmetric. The authors use this as a proxy for intraoperative brain shift, demonstrating the importance of MER in accounting for operative changes in planned anatomy. This does not account for plans that were asymmetric before surgery secondary to patient anatomy, which would be helpful in interpreting how often MER is necessary, particularly on the second pass. This report also shows that in 84.8% of cases the lead was placed at one of the original 3 MER passes, meaning that 15.2% of cases required additional pass(es). The authors compared this technique to an historical control with an average of 2.6 passes used during DBS surgery. They report their technique as using less passes; however, the authors begin with 3 passes (1 per electrode) and added at least a fourth in 15.2% of cases (Table 2) This actually increases the number of penetrations of the patient's brain, though it does reduce the number of times the microdrive is used compared to historical controls. The 2 most important findings of this study involve the efficiency and safety of using multiple MER tracts as routine during DBS surgery. The authors report an average operative time of 2.4 hours with a range of 1.5–3 hours. This demonstrates that the technique is at least as efficient as other methods in the authors’ expert hands. Their finding of 0 hemorrhages in their series of 237 lead placements using this technique shows that it is at least as safe as other techniques currently used for DBS placement. The authors correctly point out that to determine true superiority or equivalency in safety or efficiency with other techniques would require a prospective study with a very large sample size. The utility of such a study may be questionable, when the data available from this study seems adequate to guide surgical decision making. The authors do not provide outcomes data to support that their technique is efficacious. They report revising only 2/237 leads, both for inadequate effect, as their evidence that the DBS leads were working as intended. While there is no reason to suspect their technique would be less effective than other available techniques, there is also no evidence that the efficacy of the stimulator placement was superior or even as good as a control group or comparing patients to their preoperative baseline. In summary, the authors demonstrate that their technique for simultaneous anterior-posterior 3-channel MER is safe and efficient. More data would be needed to show that it is effective. Nicholas J. Brandmeir James McInerney Hershey, Pennsylvania Copyright © 2017 by the Congress of Neurological Surgeons http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Operative Neurosurgery Oxford University Press

An Analysis of the Use of Multichannel Microelectrode Recording During Deep Brain Stimulation Surgeries at a Single Center

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Oxford University Press
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Copyright © 2017 by the Congress of Neurological Surgeons
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2332-4252
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2332-4260
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10.1093/ons/opx139
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Abstract

Abstract BACKGROUND Microelectrode recording (MER) can be used to map out the target nucleus and identify ideal lead placement. OBJECTIVE To assess the use of multichannel MER to increase the efficiency of lead placement without compromising patient safety. METHODS Analysis of a single center's technique for utilizing multichannel MER with 3 consistent anterior-to-posterior simultaneous passes that include an evaluation of the location of final lead placement, patient diagnosis, target nuclei, and additional work involved for refinement of targeting. Lead revision rates and rate of hemorrhage are also assessed. RESULTS There were a total of 237 lead placements in 123 patients over a 4-yr period. In 4.2% of lead placements, additional planning was required, while only 2.5% required additional MER. The lead placement matched 51.3% of the time in bilateral placements and was consistent regardless of target nuclei. In 84.8% of cases, the final lead placement was within the initial 3 MER passes. An additional 11.3% could be placed without the need for an additional pass. There were 2 lead revisions and no hemorrhage or stroke complications. CONCLUSION This series demonstrates that our technique of multichannel MER leads to accurate and efficient lead placement maintaining its safety profile. Deep brain stimulation, Microelectrode recording, Movement disorders, Parkinson disease, Subthalamic nucleus, Tremor ABBREVIATIONS ABBREVIATIONS CSF cerebrospinal fluid CT com-puted tomography DBS deep brain stimulation GPi internal globus pallidus MER microelectrode recording MRI magnetic resonance imaging OR operating room STN subthalamic nucleus ViN ventral intermediate nucleus Deep brain stimulation (DBS) delivers benefit to those with treatment-resistant movement disorders.1,2 The US Food and Drug Administration has approved 3 indications for DBS since its inception. These treatments are for essential tremor, approved in 1997; Parkinson disease, approved in 2002; and dystonia, approved in 2003. It is well tolerated and has become the most common neurosurgical procedure for movement disorders. Because DBS is an elective procedure, it is imperative to maintain a low complication rate and maintain accuracy and efficiency in the placement of electrodes. The accuracy of electrode placement has been studied by the use of intraoperative imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT),3,4 as well as the continued use of microelectrode recording (MER).2,5-10 MER can be used to map out the target nucleus and define the best location for lead placement. The literature has supported the use of MER given the additional data that it obtains.2,5-10 Some reviews have suggested that using MER in DBS can lead to an increased occurrence of hemorrhage, especially with multiple passes during surgery,10,11 but other reviews have not observed this trend.12,13 The additional data that are obtained by MER in order to accurately place the electrode outweighs the risks of hemorrhage when it is kept significantly low.14,15 There has been an interest in multichannel MER. Potential benefits include more information to define the target nucleus and decreased intraoperative time devoted to MER, leading to a more accurate and efficient placement of the electrode. Several studies have demonstrated that, on average, multiple MER passes are required and several may be needed for accurate placement of the electrode.7,10,16-18 Multichannel MER is therefore useful for target refinement and may limit the need for additional passes to be performed.19,20 The central target track that was determined during preoperative stereotactic planning and track that demonstrated the best recording of signals do not always equate to the final lead placement, which further demonstrates the utility of multichannel MER.21 It has also been demonstrated that there is no difference in the number of MER passes that are required based on target nucleus, demonstrating the importance of MER and multichannel MER in all targets.22 This is a large, retrospective review series that evaluated a single center's approach to utilizing multichannel MER to define the target nucleus. It included an evaluation of the location of final lead placement compared to initial targeting, as well as additional work involved for refinement of targeting when utilizing a multichannel approach. An analysis of final lead placement comparing both sides in bilateral placement and a comparison of different targets was also performed. Lead revision rates and rate of hemorrhage was also assessed. These factors can be used to define the importance of multichannel MER, as well as its efficiency and safety. METHODS This study is a retrospective analysis of 123 patients who underwent initial DBS surgery in a single institution from 2012 to 2015 performed by a single surgeon. Diagnoses of these patients included Parkinson's disease, essential tremor, and dystonia. Patients ranged from 27 to 85 yr of age. There were a total of 237 lead placements, with 113 bilateral cases, in which one of the cases had 3 leads placed, as well as 10 unilateral cases. Data for the study was incorporated via a retrospective chart review of a prospective data management report. All patients undergoing an initial implant were included in the analysis, with follow-up ranging from 6 mo to 4 yr. IRB approval was not necessary given this was a retrospective analysis of a prospective database without patient identifiers. This was determined by the local IRB board and ethics committee. The analysis included an evaluation of technique utilizing 3 simultaneous MER passes in order to identify the optimal target for lead location. This analysis included target nuclei, patient diagnosis, final lead placement, and whether additional lead passes were needed. Further analysis and evaluation of additional steps was performed for all cases in which additional planning was necessary during the surgery beyond the 3 simultaneous tracks. Evaluation of lead revision and intracranial hemorrhage was also determined. Surgical Technique Patients underwent Leksell head frame (Elekta, Sweden) placement just prior to the procedure. A CT scan was obtained and merged with an MRI, which was obtained approximately 1 wk prior to the procedure. Targets were chosen preoperatively using Framelink software for initial coordinates. The surgeon would adjust the preprogrammed coordinates based on factors such as brain atrophy, size of lateral and third ventricles, and angles chosen for entry based on avoidance of key structures and blood vessels. Utilizing contrast on the preoperative MRI in order to identify blood vessels within the course of the electrodes further assisted this approach.15,22 The patient was positioned in a head-elevated supine position utilizing the Mayfield head holder adapter for the frame. Linear cranial incisions were utilized for the burr hole. The dura was incised in a cruciate fashion, with the free edges brought back with the bipolar electrocautery, followed by using the bipolar to make a small pial opening. Each track was tested to ensure the cannula was passed freely into the burr hole; then, Tisseel Fibrin Sealant (Baxter International; Deerfield, Illinois) was placed into the burr hole to limit cerebrospinal fluid (CSF) leak and potential pneumocephalus. The electrodes were placed using awake MER, with macrostimulation through the MER electrode done to identify the optimal location for final lead placement. MER was performed using 3 simultaneous passes placed 2 mm apart in an anterior-to-posterior projection with the FHC drive with the presumed planned target as the central track. We did not determine borders of our specific target nucleus, but rather determined positioning based on a strong MER, efficacy with intraoperative patient testing, and none to limited side effects based on the therapeutic window. If the amplitudes and strength of the MER were not ideal, we may have chosen to perform motor testing during the planned track to identify active cells, have a potential map of the homunculus, and attempt to increase amplitudes for improved signals. Based on the information gathered with these 3 initial passes, as well as the macrostimulation for side effect profile and efficacy, a determination would be made on lead placement and whether an additional MER and/or macrostimulation track was necessary. In cases in which the target was not determined to be within the 3 MER tracks, a decision would be made on whether the final lead placement could be 2 mm medial or lateral without additional testing, or whether additional information would need to be gathered. The decision to proceed with placement of the lead in a medial or lateral track without additional testing would be based on a treatment response that occurred within a very narrow therapeutic window. Although the Z-axis may have been adjusted slightly during the initial preoperative planning based on the AC-PC line, the final depth was determined from the MER. Intraoperative fluoroscopy was used to further confirm placement and positioning. Strict blood pressure control is maintained during the procedure with mean arterial pressures held below 80 mm Hg until completion of the procedure, when patients would be allowed to slowly normalize in the recovery area. A postoperative head CT was obtained within 3 h of the procedure, along with a brain MRI the morning following the procedure prior to discharge.15,22 One week after this surgery, the extension lead was connected, and the IPG was implanted under general anesthesia. RESULTS The demographic information for the patients is shown in Table 1. There were 237 lead placements in 123 patients in this study. The mean patient age was 66.4 with a range from 27 to 85. Ten, or 4.2%, of these lead placements required additional planning. The details of this additional planning are shown in Table 2. Six of these 10 placements, or 2.5% of all placements, required additional MER. One additional patient had 3 leads placed during the surgery due to a diagnosis of both Parkinson disease and essential tremor, with bilateral subthalamic nucleus (STN) leads and 1 ventral intermediate nucleus (ViN) lead. This decision was made intraoperatively given complete lack of unilateral tremor control with placement in STN. The procedures for the remainder of the patients requiring additional testing were performed by placing the MER electrode using only macrostimulation. The most common diagnosis was Parkinson disease, and the most common target was the subthalamic nucleus. In those patients not requiring additional work, a decision could be made on placement within the 5 tracks of the FHC drive based on the MER, and macrostimulation for side effect profile and efficacy. TABLE 1. The Table Provides Demographic Information on the Surgical Patients Included in the Study Number of patients: 123 with 237 lead placements  Placements that required additional passes: 10  Mean age: 66.4  Range of ages: 27-85  Diagnoses:    81 Parkinson's disease      61 STN      16 ViM      4 GPi    39 essential tremor      39 ViM    3 dystonia      3 GPi  Number of patients: 123 with 237 lead placements  Placements that required additional passes: 10  Mean age: 66.4  Range of ages: 27-85  Diagnoses:    81 Parkinson's disease      61 STN      16 ViM      4 GPi    39 essential tremor      39 ViM    3 dystonia      3 GPi  View Large TABLE 2. Analysis of Special Placements. The Table Provides Additional Information on the Cases That Involved Extra Steps in the Typical Lead Placement Procedure Patient  Side  Target  Diagnosis  Notes  1  Left  ViM  ET  Performed additional tract 2 mm lateral with MER but placed at target  2  Bilateral  STN  PD  Performed additional macrostimulation tract on left side 2 mm medial without MER and placed in this location  3  Right  ViM  ET  Performed macrostimulation and placed lead 2 mm lateral without MER on lateral tract  4  Bilateral  GPi  Dystonia  Placed 2 mm medial to target on right side without additional tract but performed 2 single MER passes secondary to concern of vasculature  5  Bilateral  STN  PD  Performed additional tract medially on left with MER and placed 4 mm medial to target  6  Bilateral  STN  PD  Performed additional tract laterally on left with MER, but placed 2 mm anterior  7  Bilateral  STN  PD  Performed 2 additional macrostimulation testing tracts medial and anterior/medial on left without MER and placed anterior/medial  8  Bilateral  ViM  ET  Performed 2 additional tracts lateral and posterior/lateral with MER and placed posterior/lateral  9  Bilateral  ViM  ET  Performed additional tract on left laterally with MER and placed laterally  10  Bilateral  STN  PD  Performed additional macrostimulation tract laterally without MER on right and placed at target  Patient  Side  Target  Diagnosis  Notes  1  Left  ViM  ET  Performed additional tract 2 mm lateral with MER but placed at target  2  Bilateral  STN  PD  Performed additional macrostimulation tract on left side 2 mm medial without MER and placed in this location  3  Right  ViM  ET  Performed macrostimulation and placed lead 2 mm lateral without MER on lateral tract  4  Bilateral  GPi  Dystonia  Placed 2 mm medial to target on right side without additional tract but performed 2 single MER passes secondary to concern of vasculature  5  Bilateral  STN  PD  Performed additional tract medially on left with MER and placed 4 mm medial to target  6  Bilateral  STN  PD  Performed additional tract laterally on left with MER, but placed 2 mm anterior  7  Bilateral  STN  PD  Performed 2 additional macrostimulation testing tracts medial and anterior/medial on left without MER and placed anterior/medial  8  Bilateral  ViM  ET  Performed 2 additional tracts lateral and posterior/lateral with MER and placed posterior/lateral  9  Bilateral  ViM  ET  Performed additional tract on left laterally with MER and placed laterally  10  Bilateral  STN  PD  Performed additional macrostimulation tract laterally without MER on right and placed at target  View Large There were 113 bilateral cases, as shown in Figure 1. Fifty-eight of those cases, or 51.3%, had lead placements that matched bilaterally. This analysis continues based on which nucleus was targeted for the procedure. The subthalamic nucleus cases matched 31 out of 59 times, or 52.5%. The ventral intermediate nucleus cases matched 24 out of 47 times, or 51.1%. The internal globus pallidus (GPi) cases matched 3 out of 7 times, or 42.9%. These findings show little difference in bilateral matching based on the target. Only approximately half of all the bilateral placements matched on both sides, demonstrating the need for performing MER on both sides. FIGURE 1. View largeDownload slide The bar graph displays the percent of cases that were bilateral, and the final placement matched on both sides. This graph is based on the target nucleus of the placement. FIGURE 1. View largeDownload slide The bar graph displays the percent of cases that were bilateral, and the final placement matched on both sides. This graph is based on the target nucleus of the placement. The placements of the final lead in relation to the target on the X/Y axis are displayed numerically in Table 3 and graphically in Figure 2. Out of the 237 total placements, 106 were at target, 54 were posterior, 41 were anterior, 24 were medial, 3 were lateral, and 8 qualified as other. Other would include a final track that is not fixed in the 5-track FHC drive, such as a diagonal track compared to central. These values equate to 44.7% at target, 22.8% posterior, 17.3% anterior, 10.1% medial, 1.3% lateral, and 3.4% other. In 84.8% of cases, the final lead placement was either at target, anterior, or posterior, and therefore within the initial 3 MER passes. An additional 11.3% was covered medially or laterally without the need for an additional pass based on the data gathered. Table 4 shows the final placements in relation to target on the Z-axis. The data show that 113 were at target, while 32 were above and 92 were below. These values equate to 47.7% at target, 13.5% above, and 38.8 below. The average depth away from target was 0.27 mm below. FIGURE 2. View largeDownload slide The pie chart displays the location of final lead placements in relation to the targeted nucleus. FIGURE 2. View largeDownload slide The pie chart displays the location of final lead placements in relation to the targeted nucleus. TABLE 3. The Table Displays the Direction of Final Lead Placement Based on the Initial Microelectrode Recording for Each Target Nucleus on the X/Y-axis   Anterior  Posterior  Medial  Lateral  At target  Other  Total  STN  31  14  18  1  54  2  120  ViM  6  37  4  3  48  5  103  GPi  4  3  2  0  4  1  14  Total  41  54  24  4  106  8  237    Anterior  Posterior  Medial  Lateral  At target  Other  Total  STN  31  14  18  1  54  2  120  ViM  6  37  4  3  48  5  103  GPi  4  3  2  0  4  1  14  Total  41  54  24  4  106  8  237  View Large TABLE 4. The Table Displays the Direction of Final Lead Placement Based on the Initial Microelectrode Recording for Each Target Nucleus on the Z-axis   Above  Below  At target  Total  STN  6  74  40  120  ViM  24  17  62  103  GPi  2  1  11  14  Total  32  92  113  237    Above  Below  At target  Total  STN  6  74  40  120  ViM  24  17  62  103  GPi  2  1  11  14  Total  32  92  113  237  View Large This same analysis for final lead location was further based on the target nuclei. This is shown in Figure 3. Fifty-two out of 115 subthalamic nucleus cases were at target. Forty-nine out of 99 ventral intermediate nucleus cases were at target. Four out of 13 internal globus pallidus cases were at target. These findings show that the final lead placement is not consistently at target and is irrespective of the target nuclei. FIGURE 3. View largeDownload slide The bar graph displays the final lead placement based on the target nucleus. FIGURE 3. View largeDownload slide The bar graph displays the final lead placement based on the target nucleus. An analysis was also performed looking at the length of the surgery from first incision until dressing and is shown in Figure 4. The results show a small peak in low numbers due to the unilateral cases and a small peak in higher numbers due to early cases with this technique. Over the study period, there was a decrease in surgery time, demonstrating improvement in the described technique with procedure refinement and increasing experience of the implanting surgeon. This decrease in procedure time became more consistent, although there would be some variation in operating room (OR) time based on additional passes, patient cooperation, and degree of intraoperative testing necessary. Bilateral procedures, as expected, were longer than unilateral procedures. The mean and median times for bilateral procedures were 157 and 147 min, while the mean and median times for unilateral procedures were 88 and 75 min. FIGURE 4. View largeDownload slide The histogram displays the operative times of the surgeries included in this study. FIGURE 4. View largeDownload slide The histogram displays the operative times of the surgeries included in this study. In the follow-up period for all patients, ranging from 6 mo to 4 yr, there was a total of 2 lead revisions. Both of these revisions were required due to loss of efficacy over time. Both were ViM lead placements for essential tremor and required being moved 2 mm lateral from their placed position. There were no hemorrhage or stroke complications in our series. DISCUSSION DBS is a commonly utilized neurosurgical intervention that is an elective procedure. Surgical technique is imperative to its success. Multiple factors are involved in maintaining good patient outcomes, which can include low complication rates, an efficient and safe surgery, as well and precise targeting of the desired nucleus. MER is utilized to identify the optimal location for final DBS lead placement, with studies verifying its safety and effectiveness.2,5-10,23 Multichannel MER can also be useful for target refinement.19,20 Our series evaluated the use of multichannel MER in refining surgical technique to better define the target nucleus and make the procedure more efficient while maintaining its safety profile. Its utility is in accurate lead placement with a low lead revision rate. The technique utilized incorporated 3 MER leads passed simultaneously in order to define the target nucleus. The 3 tracks include the targeted central track and additional anterior and posterior tracks. Out of the 237 leads placed in this study, only 10 required additional planning or work beyond the data recorded on the initial pass. This additional work included either utilizing an additional MER pass with macrostimulation or using a separate pass with the MER electrode for test stimulation only. Of those 10 procedures, only 6 required additional MER, which equates to 2.5%. This is in comparison with the published literature stating an average number of MER passes of 2.6,7 demonstrating the efficiency in this method as well as decreased passes of electrodes in the brain. Final Lead Placements There were 113 bilateral cases, with 51.3% having lead placements that matched on each side. This was also consistent across the different targets of STN, ViM, and GPi. These findings highlight the importance of utilizing MER on both sides to define the target nucleus, as the final track chosen only correlates in half of the procedures. This result demonstrates the need for performing MER on both sides, as leads may be most adequately placed in asymmetric positions. This may be a result of CSF loss or pneumocephalus during the opening of the dura. Analysis of final lead placement in relation to target demonstrated that 44.7% were at target, 22.8% posterior, 17.3% anterior, 10.1% medial, 1.3% lateral, and 3.4% in a track not defined in the standard 5-track pattern of the FHC drive. The technique utilized 3 simultaneous tracks from anterior to posterior. The final lead placement was in one of these 3 tracks in 84.8% of cases. An additional 11.3% were covered medially or laterally without the need for an additional pass. This demonstrates that the majority of final lead placements will fall within the 3 tracks from anterior to posterior, and that the information gathered from these tracks will allow for the placement of the final lead without additional work in another track. In this analysis, anterior and posterior were close to equal and more common than medial or lateral, demonstrating that 3 tracks anterior to posterior is the best option for multichannel MER. The 2-mm spacing of the tracks defined in the 5-track pattern of the FHC drive is also adequate for the majority of lead placements given that average target adjustments with single-channel MER has been reported as 1 to 4 mm.10 The final lead placement was only at the target track in 44.7% of cases. This was consistent across the different targets of STN, ViM, and GPi. This demonstrates that the target nuclei do not affect the accuracy of the initial lead placement, there is utility in MER regardless of target nuclei, and that the method of three simultaneous MER tracks is a desirable technique for optimal lead location and efficiency. This is consistent with the literature demonstrating no difference in the average amount of MER passes performed to define the target based on location,22 as well as the need for multiple passes to define the target. This has been reported around an average number of MER passes of 2.6,7 as well as a modification of electrode position in 17% to 87% of cases based on the information of one single-channel MER pass.10 Utilization of this method of multichannel MER will reduce the additional passes that are commonly needed in single-channel MER cases. Operative Safety and Efficiency The median time for a bilateral procedure was just under 2.5 h, with the majority of cases between 1.5 and 3 h. With increased experience of the surgeon and refined technique, the procedure time improved from the initial cases. There is the expected variation in OR time based on additional passes, patient cooperation, and degree of intraoperative testing of the patient. These times demonstrate an efficient procedure for those utilizing MER. This is especially true when considering that our final lead placement was frequent in a different track than the one targeted. This fact held true for the contralateral side as well. There is, however, the limitation of applying our observed OR times due to factors such as other surgeons’ skill, experience, and OR setup. Lead revision was only seen in 2 patients (0.8%) over the observed follow-up period. Both were for loss of efficacy over time and both had ViM targets that were revised to a more lateral position. This lead revision rate is quite low when compared to the literature, which has reported rates varying from 2.0% to 5.7% in several reviews,14,15,22,24 but may be as high as 15.2% for lead revision, with a suspected 48.5% of these from improper targeting as seen in a more recent manuscript looking at North American databases.25 These previous findings demonstrate the accurate placement of the leads utilizing this technique with multichannel MER. There is, however, a limitation of this review, as the results of the patients for efficacy of their system was not quantified and followed. In addition, comparison of placements with or without MER would also need to be evaluated against this technique. The most serious complication of DBS is intracerebral hemorrhage. The literature shows that the incidence of intracerebral hemorrhages from stereotactic surgery, which includes ablation, is between 1% and 5%.1,26,27 The incidence of this complication in DBS procedures is low, at 0.7% to 3.9% per lead passage, and the permanent morbidity of the patient is 0% to 0.8%.2,9,12,13,28-30 Some previous studies have suggested that using MER in DBS can lead to an increased occurrence of hemorrhage, especially with multiple passes,10,11 but this finding is inconsistent with other reviews.12,13 There were no hemorrhage or stroke complications in our series, suggesting no increased risk to the patient with simultaneously passing 3 leads. The procedure includes strict blood pressure monitoring intraoperatively to maintain the mean arterial pressure at or below 80 mm Hg. It also includes vigilant preoperative planning of the proposed trajectory to avoid all potential vessels that could be in the field. The authors postulate that using 3 simultaneous MER tracks should not increase the hemorrhage rate, as it creates an anchoring of the brain as it traverses the tissue. This method may actually decrease the hemorrhage rate that has been previously observed with MER, but one can also hypothesize that the observed rate of 0% could be secondary to the number of cases performed and that as time progresses with an increase in sample size this will not hold true. Based on these factors, this technique is at least as safe as other standards, but a larger series would be needed to determine if this method is superior to others. Some have looked at the role of intraoperative imaging for improved accuracy and time efficiency in the OR,3,4 but this may not be feasible for all centers with limited intraoperative capabilities for imaging modalities such as MRI or CT. Overall, it can be determined that our technique utilizing multichannel MER with 3 simultaneous tracks running anterior to posterior can lead to time savings and efficiency in the OR, accurate lead placement, and no increased risk of intracerebral hemorrhage or stroke. CONCLUSION Our technique utilizing multichannel MER with 3 simultaneous tracks running anterior to posterior can lead to accurate lead placement, efficiency in the OR, and no increased risk of intracerebral hemorrhage or stroke. The findings highlight the importance of utilizing MER regardless of target nuclei, as well as in bilateral procedures. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Videnovic A, Metman LV. Deep brain stimulation for Parkinson's disease: prevelance of adverse events and need for standardized reporting. Mov Disord.  2008; 23( 3): 343- 349. 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Terao T, Takahashi H, Yokochi F, Taniguchi M, Okiyama R, Hamada I. Hemorrhagic complication of stereotactic surgery in patients with movement disorders. J Neurosurg.  2003; 98( 6): 1241- 1246. Google Scholar CrossRef Search ADS PubMed  COMMENT The authors offer an analysis of their technique for microelectrode recording (MER) as an adjunct for accurate placement of deep brain stimulating (DBS) leads. They retrospectively analyzed 123 patients who had 237 lead placements in the subthalamic nucleus (STN), ventral intermediate nucleus (ViM), and globus pallidus (GPi). They used a standard procedure for implanting DBS leads while utilizing an MER technique with 3 electrodes in an anterior to posterior array: the central electrode in the originally planned tract and the other electrodes running 2 mm anterior and posterior. The authors looked at the risk of additional recording tracts–specifically of hemorrhage–versus the value of the data obtained from those additional MER tracts. They posit that this is particularly important given that often several MER tracts are required to appropriately place a lead. Their analysis showed that approximately 50% of bilateral leads (52.5% of STN, 51.1% of ViM, and 42.9% of GPi) were symmetric. The authors use this as a proxy for intraoperative brain shift, demonstrating the importance of MER in accounting for operative changes in planned anatomy. This does not account for plans that were asymmetric before surgery secondary to patient anatomy, which would be helpful in interpreting how often MER is necessary, particularly on the second pass. This report also shows that in 84.8% of cases the lead was placed at one of the original 3 MER passes, meaning that 15.2% of cases required additional pass(es). The authors compared this technique to an historical control with an average of 2.6 passes used during DBS surgery. They report their technique as using less passes; however, the authors begin with 3 passes (1 per electrode) and added at least a fourth in 15.2% of cases (Table 2) This actually increases the number of penetrations of the patient's brain, though it does reduce the number of times the microdrive is used compared to historical controls. The 2 most important findings of this study involve the efficiency and safety of using multiple MER tracts as routine during DBS surgery. The authors report an average operative time of 2.4 hours with a range of 1.5–3 hours. This demonstrates that the technique is at least as efficient as other methods in the authors’ expert hands. Their finding of 0 hemorrhages in their series of 237 lead placements using this technique shows that it is at least as safe as other techniques currently used for DBS placement. The authors correctly point out that to determine true superiority or equivalency in safety or efficiency with other techniques would require a prospective study with a very large sample size. The utility of such a study may be questionable, when the data available from this study seems adequate to guide surgical decision making. The authors do not provide outcomes data to support that their technique is efficacious. They report revising only 2/237 leads, both for inadequate effect, as their evidence that the DBS leads were working as intended. While there is no reason to suspect their technique would be less effective than other available techniques, there is also no evidence that the efficacy of the stimulator placement was superior or even as good as a control group or comparing patients to their preoperative baseline. In summary, the authors demonstrate that their technique for simultaneous anterior-posterior 3-channel MER is safe and efficient. More data would be needed to show that it is effective. Nicholas J. Brandmeir James McInerney Hershey, Pennsylvania Copyright © 2017 by the Congress of Neurological Surgeons

Journal

Operative NeurosurgeryOxford University Press

Published: Apr 1, 2018

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