Subdural Electrode Placement Research Articles

Direct (D)-Wave Monitoring Enhancement With Subdural Electrode Placement: A Case Series.

Direct-wave (D-wave) neuromonitoring is a direct measure of corticospinal tract integrity that detects potential injury during spinal cord surgery. Epidural placement of electrodes used for D-wave measurements can result in high electrical impedances resulting in substantial signal noise that can compromise signal interpretation. Subdural electrode placement may offer a solution. Medical records for consecutive patients with epidural and subdural D-wave monitoring were reviewed. Demographic and clinical information including preoperative and postoperative motor strength were recorded. Neuromonitoring charts were reviewed to characterize impedances and signal amplitudes of D-waves recorded epidurally (before durotomy) and subdurally (following durotomy). Nonparametric statistics were used to compare epidural and subdural D-waves. Ten patients (50% women, median age 50.5 years) were analyzed, of which five patients (50%) were functionally independent (modified McCormick grade ≤ II) preoperatively. D-waves were successfully acquired by subdural electrodes in eight cases and by epidural electrodes in three cases. Subdural electrode placement was associated with lower impedance values ( P = 0.011) and a higher baseline D-wave amplitude ( P = 0.007) relative to epidural placement. No association was observed between D-wave obtainability and functional status, and no adverse events relating to subdural electrode placement were encountered. Subdural electrode placement allows successful D-wave acquisition with accurate monitoring, clearer waveforms, and a more optimal signal-to-noise ratio relative to epidural placement. For spinal surgeries where access to the subdural compartment is technically safe and feasible, surgeons should consider subdural placement when monitoring D-waves to optimize clinical interpretation.

“Mail-slot” Technique for Minimally Invasive Placement of Subdural Grid Electrodes: A Single-institution Experience

BackgroundIn the management of multi-drug-resistant focal epilepsies, intracranial electrode implantation is employed for precise localization of the ictal onset zone. In select patients, subdural grid electrode implantation is utilized. Subdural grid placement traditionally requires large craniotomies to visualize the cortex prior to mapping. However, smaller craniotomies may enable shorter operations and reduced risks. We aimed to compare surgical outcomes between patients undergoing traditional large craniotomies with those undergoing tailored 'mini' craniotomies (the “Mail-Slot” technique) for subdural grid placement. MethodsThis retrospective cohort study included 23 patients who underwent subdural electrode implantation for epilepsy monitoring between 2014 and 2020. Patients were categorized into mini craniotomies (N=9) and traditional large craniotomies (N=14) groups. Demographics, operative details, and outcomes were reviewed. Craniotomy size and number of electrodes were determined via post-hoc radiographs. ResultsOf the 23 patients studied, the mini group had smaller craniotomy sizes (mean=22.71 cm2 vs. 65.17 cm2, p<0.001) and higher electrode-to-size ratios (mean=4.25 vs. 1.71, p<0.0001). The mini group had slightly fewer total electrodes (mean=88.67 vs. 107.43, p=0.047). No significant differences were found in operative duration, blood loss, invasive EEG duration, complications, or Engel scores between the groups. One patient per group required further invasive epilepsy monitoring for localization; all patients underwent therapeutic surgery. ConclusionOur findings suggest that mini craniotomies for subdural grid placement in epilepsy monitoring offer significant advantages, including smaller craniotomy sizes and shorter operation durations, without compromising safety or efficacy. These results support the trend towards minimally invasive, patient-tailored surgical approaches in epilepsy treatment.

The value of additional electrodes when stereo-electroencephalography is inconclusive.

Stereo-electroencephalography (SEEG) is the preferred method for intracranial localization of the seizure-onset zone (SOZ) in drug-resistant focal epilepsy. Occasionally SEEG evaluation fails to confirm the pre-implantation hypothesis. This leads to a decision tree regarding whether the addition of SEEG electrodes (two-step SEEG - 2sSEEG) or placement of subdural electrodes (SDEs) after SEEG (SEEG2SDE) would help. There is a dearth of literature encompassing this scenario, and here we aimed to characterize outcomes following unplanned two-step intracranial EEG (iEEG). All 225 adult SEEG cases over 8 years at our institution were reviewed to extract patient data and outcomes following a two-step evaluation. Three raters independently quantified benefits of additional intracranial electrodes. The relationship between two-step iEEG benefit and clinical outcome was then analyzed. Fourteen patients underwent 2sSEEG and nine underwent SEEG2SDE. In the former cohort, the second SEEG procedure was performed for these reasons-precise localization of the SOZ (36%); defining margins of eloquent cortex (21%); and broadening coverage in the setting of non-localizable seizure onsets (43% of cases). Sixty-four percent of 2sSEEG cases were consistently deemed beneficial (Light's κ = 0.80). 2sSEEG performed for the first two indications was much more beneficial than when onsets were not localizable (100% vs 17%, p = .02). In the SEEG2SDE cohort, SDEs identified the SOZ and enabled delineation of margins relative to eloquent cortex in all cases. The two-step iEEG is useful if the initial evaluation is broadly concordant with the original electroclinical hypothesis, where it can clarify onset zones or delineate safe surgical margins; however, it provides minimal benefit when the implantation hypothesis is erroneous, and we recommend that 2sSEEG not be generally utilized in such cases. SDE implantation after SEEG minimizes the need for SDEs and is helpful in delineating surgical boundaries relative to ictal-onset zones and eloquent cortex.

Infections in Functional Neurosurgery:Focusing on Device-based Surgery

Functional neurosurgery for epilepsy, movement disorders, and spasticity includes some device-based surgeries such as deep brain stimulation, subdural electrode placement, vagus nerve stimulation, and baclofen pump implantation. These surgeries have a higher risk of surgical site infection(SSI)than other general neurological surgeries. Furthermore, because device removal after infection can significantly impair patients'activities of daily living and quality of life, SSI in functional neurosurgery is a worrisome surgical complication. In this study, we conducted a mini-review of the risk of infection in each device-based surgery and described associated surgical procedures and preparations performed at our institution, with a focus on infection prevention.

816 Traveling Waves Reveal a Dynamic Source of Human Focal Seizures and Interictal Spikes

INTRODUCTION: Treatment of patients with drug resistant focal epilepsy relies upon accurate seizure localization. Ictal activity captured in intracranial EEG (iEEG) has traditionally been interpreted to suggest that the underlying cortex is actively seizing. On the other hand, an emerging hypothesis suggests that seizures may in fact emerge from focal regions, which emit discharges that travel over the surface of the cortex as traveling waves. METHODS: 20 patients underwent placement of subdural electrodes for invasive monitoring at the National Instutes of Health, underwent surgical resection for epilepsy, and had at least 1 year of follow-up. Outcomes were measured by the Engel scale. In these patients, we measured the time delay in discharge receipt at adjacent electrodes to compute the location of the seizure source. This algorithm, known as multilateration, has been used for signal source localization with sparsely-spaced sensors for over a century in geophysics, radar, and acoustics, but has not been used in epilepsy until the present. RESULTS: In patients with good outcome, but not in patients with poor outcome, the seizure source tends to localize to the resection territory. The source is a focal, dynamic entity that moves and evolves over the time course of a seizure. Our approach also successfully localizes interictal spikes. We find that interictal spikes emerge from multiple distinct foci in each patient. Seizures either arise from or travel to interictal spike generators. CONCLUSIONS: The seizure source appears to be more focal than has traditionally been conceptualized. This focal source may be localized by measuring the time difference of discharge receipt in intracranial electrodes. Algorithmic source localization, as performed here, may guide pre-surgical planning for drug-resistant epilepsy and may improve outcomes.

Nutritional Intervention Facilitates Food Intake after Epilepsy Surgery.

Background: We investigated whether nutritional intervention affected food intake after epilepsy surgery and if intravenous infusions were required in patients with epilepsy. We hypothesized that postoperative food intake would be increased by nutritional intervention. The purpose of this study was to compare postoperative food intake in the periods before and after nutritional intervention. Methods: Between September 2015 and October 2020, 124 epilepsy surgeries were performed. Of these, 65 patients who underwent subdural electrode placement followed by open cranial epilepsy surgery were studied. Postoperative total food intake, rate of maintenance of food intake, and total intravenous infusion were compared in the periods before and after nutritional intervention. Results: A total of 26 females and 39 males (age range 3–60, mean 27.1, standard deviation (SD) 14.3, median 26 years) were enrolled. Of these, 18 females and 23 males (3–60, mean 28.2, SD 15.1, median 26 years) were in the pre-nutritional intervention period group, and eight females and 16 males (5–51, mean 25.2, SD 12.9, median 26.5 years) were in the post-nutritional intervention period group. The post-nutritional intervention period group showed significantly higher food intake (p = 0.015) and lower total infusion (p = 0.006) than the pre-nutritional intervention period group. Conclusion: The nutritional intervention increased food intake and also reduced the total amount of intravenous infusion. To identify the cut-off day to cease the intervention and to evaluate whether the intervention can reduce the complication rate, a multicenter study with a large number of patients is warranted.

Cost-effectiveness analysis of invasive EEG monitoring in drug-resistant epilepsy

PurposeOur aim was to determine the cost-effectiveness of two intracranial electroencephalography (iEEG) interventions: 1) stereoelectroencephalography (SEEG) and 2) placement of subdural grid electrodes (SDGs) both followed by resective surgery in patients with drug-resistant, partial-onset epilepsy, compared with medical management (MM) in Hungary from payer's perspective. MethodsThe incremental health gains and costs of iEEG interventions have been determined with a combination of a decision tree and prevalence Markov process model over a 30-year time horizon in a cost–utility analysis (CUA). To address the effect of parameter uncertainty on the incremental cost-effectiveness ratio (ICER), deterministic and probabilistic sensitivity analyses were performed. ResultsOur results showed that both SEEG and SDG interventions represent a more expensive but more effective strategy than MM representing the current standard of care. The total discounted cost of SEEG and SDG were € 32,760 and € 25,028 representing € 18,108 and € 10,375 additional cost compared with MM, respectively. However, they provide an additional 3.931 (in SEEG group) and 3.444 quality-adjusted life years (QALYs; in SDG group), correspondingly. Thus, the ICER of SEEG is € 4607 per QALY gain, while the ICER for SDG is € 3013 per QALY gain, compared with MM. At a cost-effectiveness threshold of € 41,058 per QALY in Hungary, both subtypes of iEEG interventions are cost-effective and provide good value for money. SignificanceBecause of the high cost of implanting electrodes and monitoring, the invasive EEG for patients with refractory epilepsy is currently not available in the Hungarian national healthcare system. Our study demonstrated that these procedures in Hungary are cost-effective compared with the MM. As a result, the introduction of iEEG interventions to the reimbursement list of the National Health Insurance Fund Administration was initiated.

Postoperative outcomes following pediatric intracranial electrode monitoring: A case for stereoelectroencephalography (SEEG)

BackgroundFor patients with medically refractory epilepsy, intracranial electrode monitoring can help identify epileptogenic foci. Despite the increasing utilization of stereoelectroencephalography (SEEG), the relative risks or benefits associated with the technique when compared with the traditional subdural electrode monitoring (SDE) remain unclear, especially in the pediatric population. Our aim was to compare the outcomes of pediatric patients who received intracranial monitoring with SEEG or SDE (grids and strips). MethodsWe retrospectively studied 38 consecutive pediatric intracranial electrode monitoring cases performed at our institution from 2014 to 2017. Medical/surgical history and operative/postoperative records were reviewed. We also compared direct inpatient hospital costs associated with the two procedures. ResultsStereoelectroencephalography and SDE cohorts both showed high likelihood of identifying epileptogenic zones (SEEG: 90.9%, SDE: 87.5%). Compared with SDE, SEEG patients had a significantly shorter operative time (118.7 versus 233.4 min, P < .001) and length of stay (6.2 versus 12.3 days, P < .001), including days spent in the intensive care unit (ICU; 1.4 versus 5.4 days, P < .001). Stereoelectroencephalography patients tended to report lower pain scores and used significantly less narcotic pain medications (54.2 versus 197.3 mg morphine equivalents, P = .005). No complications were observed. Stereoelectroencephalography and SDE cohorts had comparable inpatient hospital costs (P = .47). ConclusionIn comparison with subdural electrode placement, SEEG results in a similarly favorable clinical outcome, but with reduced operative time, decreased narcotic usage, and superior pain control without requiring significantly higher costs. The potential for an improved postoperative intracranial electrode monitoring experience makes SEEG especially suitable for pediatric patients.

Minimally Invasive, Endoscopic-Assisted Device for Subdural Electrode Implantation in Epilepsy.

Subdural grids and strip electrodes provide wide coverage of the cerebral cortex, precise delineation of the extent of the seizure onset zone, and improved spatial sampling to perform functional mapping for eloquent cortex. To describe a novel device that allows for a minimally invasive approach to implantation of subdural grid and strip electrodes. A skull mounted device was created to allow for implantation of subdural electrodes through a keyhole craniotomy with direct visualization using the aid of a flexible neurovideoscope. The initial studies in preparation for grid development performed on cadaveric skulls were analyzed to determine the size of craniotomy required for deployment, maximal distance of strip electrode deployment from center of craniotomy, and visual inspection of the cortex was performed for any underlying damage. The device allowed for the placement of subdural electrodes through a 40-mm craniotomy. Subdural electrodes were deployed in multiple directions to a distance of a 70-mm radius from the center of the craniotomy. There was no visual damage to the underlying cortex after the procedures were completed. Large craniotomies are typically desired to provide direct visualization of the implantation of subdural electrodes, but can increase the risk of subdural hemorrhages and infections. This study describes a novel minimally invasive endoscopically assisted device for the implantation of subdural strip electrodes under direct visualization. With this device, we are able to limit the size of the craniotomy, avoid incision through the temporalis muscle, and implant subdural electrodes with visualization of the cortex.

Cranioplasty with Titanium Might Be Suitable for Adult Epilepsy Surgery After Subdural Placement Surgery To Avoid Surgical Site Infection

The purpose of the present study was to compare the surgical site infection (SSI) rates between resorbable plates and titanium plates used for adult patients with intractable epilepsy who had undergone epilepsy surgery after subdural electrode placement. We performed subdural electrode surgery, followed by epilepsy surgery, for 87 adult patients with intractable epilepsy. The epilepsy surgery included 75 focus resections and 12 corpus callosotomies. We compared the SSI rates between patients who had undergone cranioplasty with titanium and resorbable plates after epilepsy surgery. Of the 87 patients, 43 had undergone cranioplasty with resorbable plates (group A) and 44 had undergone cranioplasty with titanium plates (group B). The frequency of SSI was significantly greater in group A (7patients; 16.3%) than in group B (1 patient; 2.3%; P=0.03, Fisher's exact test). Univariate regression analysis also showed a significantly greater infection rate with the resorbable plates (P= 0.024). For epilepsy surgery of adult patients after subdural electrode placement surgery, the SSI rate for cranioplasty was greater with resorbable plates than with titanium plates.

Craniotomy Size for Subdural Grid Electrode Placement in Invasive Epilepsy Diagnostics

Background: Traditionally, for subdural grid electrode placement, large craniotomies have been applied for optimal electrode placement. Nowadays, microneurosurgeons prefer patient-tailored minimally invasive approaches. Absolute figures on craniotomy size have never been reported. To elucidate the craniotomy size necessary for successful diagnostics, we reviewed our single-center experience. Methods: Within 3 years, 58 patients with focal epilepsies underwent subdural grid implantation using patient-tailored navigation-based craniotomies. Craniotomy sizes were measured retrospectively. The number of electrodes and the feasibility of the resection were evaluated. Sixteen historical patients served as controls. Results: In all 58 patients, subdural electrodes were implanted as planned through tailored craniotomies. The mean craniotomy size was 28 ± 15 cm² via which 55 ± 16 electrodes were implanted. In temporal lobe diagnostics, even smaller craniotomies were applied (21 ± 11 cm²). Craniotomies were significantly smaller than in historical controls (65 ± 23 cm², p < 0.05), while the mean number of electrodes was comparable. The mean operation time was shorter and complications were reduced in tailored craniotomies. Conclusion: Craniotomy size for subdural electrode implantation is controversial. Some surgeons favor large craniotomies, while others strive for minimally invasive approaches. For the first time, we measured the actual craniotomy size for subdural grid electrode implantation. All procedures were straightforward. We therefore advocate for patient-tailored minimally invasive approaches – standard in modern microneurosurgery – in epilepsy surgery as well.

Simultaneous Frame-assisted Stereotactic Placement of Subdural Grid Electrodes and Intracerebral Depth Electrodes.

In complex cases of drug-resistant focal epilepsy, the precise localization of the epileptogenic zone requires simultaneous implantation of depth and subdural grid electrodes. This study describes a new simple frame-assisted method that facilitates the simultaneous placement of both types of intracranial electrodes. Ten consecutive patients were evaluated and divided into two groups. Group A included patients with simultaneous frame-assisted placement of depth and subdural grid electrodes. In group B, depth electrodes were implanted stereotactically; grid electrodes were implanted in a separate surgery. The placement of the subdural grid was accurate as individually designed by the epileptologists in all five patients from group A. In group B, one patient showed a slight and another one a significant deviation of the subdural grid position postoperatively. The mean surgical time in group A was shorter (280±62 minutes) compared with the mean duration of the surgical procedures in group B (336±51 minutes). The frame-assisted placement of subdural grid electrodes facilitates the surgical procedure for invasive video-electroencephalography monitoring in complex cases of drug-resistant focal epilepsy in which a combination of depth electrodes and subdural grid electrodes is needed, by reducing the surgical time and guaranteeing highly accurate electrode localizations.

A Flexible 202-Channel Epidural ECoG Array With PEDOT: PSS Coated Electrodes for Chronic Recording of the Visual Cortex

Electrocorticography (ECoG) electrode arrays for epidural implantation allow establishing neural interfaces, which promote investigation of complex distributed brain functions and development of neuroprosthetic systems while having reduced invasiveness in comparison to intracortical or subdural electrode placement. In this paper, we present the design, fabrication, and both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vitro</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vivo</i> evaluation of a flexible ECoG array with 202 closely spaced electrodes of 560- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> diameter, each coated with the polymer poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) for chronic recording in two visual cortical areas V1 and V4 of macaque monkeys. The specific layout of the array provides a close fit to the curved surface of the brain. We confirm its chronic recording functionality <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vivo</i> by estimating visual receptive fields for the individual electrodes.

2327 Decoding/encoding somatosensation from the hand area of the human primary somatosensory (S1) cortex for a closed-loop motor/sensory brain-machine interface (BMI)

OBJECTIVES/SPECIFIC AIMS: A brain-machine interface (BMI) is a device implanted into the brain of a paralyzed or injured patient to control an external assistive device, such as a cursor on a computer screen, a motorized wheelchair, or a robotic limb. We hypothesize we can utilize electrical stimulation of subdural electrocorticography (ECoG) electrodes as a method of generating the percepts of somatosensation such as vibration, temperature, or proprioception. METHODS/STUDY POPULATION: There will be 10 subjects, who are informed, willing, and consented epilepsy patients undergoing initial surgery for placement of subdural ECoG electrodes in the brain for seizure monitoring. ECoG will be used as a platform for recording high-resolution local field potentials during real-touch behavioral tasks. In addition, ECoG will also be used to electrically stimulate the human cerebral cortex in order to map and understand how varying stimulation parameters produce percepts of sensation. RESULTS/ANTICIPATED RESULTS: To determine how tactile and proprioceptive signals are integrated in S1, we will perform spectral analysis of the broadband local field potentials to look for increased power in specific frequency bands in the ECoG recordings while touching or moving the hand. To explore generating artificial sensation, the subject will be asked to perform a variety of tasks with and without the aid of stimulation. We anticipate the subject’s performance will be enhanced with the addition of artificial sensation. DISCUSSION/SIGNIFICANCE OF IMPACT: Many patients might benefit from a BMI, such as those with stroke, amputation, spinal cord injury, or brain trauma. The current generation of BMI devices are guided by visual feedback alone. However, without somatosensory feedback, even the most basic limb movements are difficult to perform in a fluid and natural manner. The results from this project will be crucial to developing a closed loop motor/sensory BMI.

Increased nationwide use of stereoencephalography for intracranial epilepsy electroencephalography recordings

Intracranial electroencephalography (iEEG) can be performed using minimally invasive stereo-electroencephalography (SEEG) or by implanting subdural electrodes via a craniotomy or multiple burr holes. There is anecdotal evidence that SEEG is becoming more common in the United States, though this has yet to be quantified. To address this question, all SEEG and burr hole/craniotomy subdural iEEG procedures were extracted from the Centers for Medicare and Medicaid Services Part B data files for the years 2000–2016. National trends were compared over time. In 2016, SEEG became the most frequently performed intracranial monitoring procedure in the Medicare population, increasing from 28.8% of total cases in 2000 to 43.1% in 2016 (p = 0.02). The proportion of strip electrode cases (through burr holes) significantly declined, while the frequency of craniotomies for subdural grid placement did not significantly change. These data are consistent with a nationwide increase in the utilization of SEEG with a concomitant decline in burr hole placement of subdural strip electrodes in the United States. The factors driving these changes are unknown, but are likely due in part to the desire for minimally invasive surgical options.

P2-63. Functional connectivity from the dorso-lateral and medial parts of the parietal lobe: a cortico-cortical evoked potential study

The superior parietal lobule (SPL) and the medial parietal cortex are associated with integration of various kinds of information. Little is known about connections from the superior and medial parietal cortices in humans. Our objective is to delineate their connectivity by means of cortico-cortical evoked potential (CCEP). Subjects were eight patients who underwent chronic subdural electrode placement covering the dorso-lateral (SPL) or medial parietal cortices. Single-pulse electrical stimuli were delivered and CCEPs were obtained from the frontal and parietal areas by averaging electrocorticograms time-locked to stimuli. SPL stimulation elicited 75 CCEPs at the precuneus, precentral gyrus, the dorsal premotor area (dorsal PM). The precuneus elicited 66 CCEPs in the inferior parietal lobule (IPL), dorsal premotor area (PM) and SPL. The posterior cingulate cortex elicited 36 CCEPs at the middle cingulate cortex, SPL and the precuneus. This study demonstrated reciprocal connections between the superior and medial parietal cortices. While the precuneus tends to connect with the lateral frontal area, posterior cingulate cortex with medial frontal area. These findings would account for functional differentiation between these areas, and may help us understand seizure propagation in patients with parietal lobe epilepsy.

Trans-falcine and contralateral sub-frontal electrode placement in pediatric epilepsy surgery: technical note.

Phase II monitoring with intracranial electroencephalography (ICEEG) occasionally requires bilateral placement of subdural (SD) strips, grids, and/or depth electrodes. While phase I monitoring often demonstrates a preponderance of unilateral findings, individual studies (video EEG, single photon emission computed tomography [SPECT], and positron emission tomography [PET]) can suggest or fail to exclude a contralateral epileptogenic onset zone. This study describes previously unreported techniques of trans-falcine and sub-frontal insertion of contralateral SD grids and depth electrodes for phase II monitoring in pediatric epilepsy surgery patients when concern about bilateral abnormalities has been elicited during phase I monitoring. Pediatric patients with medically refractory epilepsy undergoing stage I surgery for phase II monitoring involving sub-frontal and/or trans-falcine insertion of SD grids and/or depth electrodes at the senior author's institution were retrospectively reviewed. Intra-operative technical details of sub-frontal and trans-falcine approaches were studied, while intra-operative complications or events were noted. Operative techniques included gentle subfrontal retraction and elevation of the olfactory tracts (while preserving the relationship between the olfactory bulb and cribriform plate) to insert SD grids across the midline for coverage of the contralateral orbito-frontal regions. Trans-falcine approaches involved accessing the inter-hemispheric space, bipolar cauterization of the anterior falx cerebri below the superior sagittal sinus, and sharp dissection using a blunt elevator and small blade scalpel. The falcine window allowed contralateral SD strip, grid, and depth electrodes to be inserted for coverage of the contralateral frontal regions. The study cohort included seven patients undergoing sub-frontal and/or trans-falcine insertion of contralateral SD strip, grid, and/or depth electrodes from February 2012 through June 2015. Five patients (71%) experienced no intra-operative events related to contralateral ICEEG electrode insertion. Intra-operative events of frontal territory venous engorgement (1/7, 14%) due to sacrifice of anterior bridging veins draining into the SSS and avulsion of a contralateral bridging vein (1/7, 14%), probably due to prior anterior corpus callosotomy, each occurred in one patient. There were no intra-operative or peri-operative complications in any of the patients studied. Two patients required additional surgery for supplemental SD strip and/or depth electrodes via burr hole craniectomy to enhance phase II monitoring. All patients proceeded to stage II surgery for resection of ipsilateral epileptogenic onset zones without adverse events. Trans-falcine and sub-frontal insertion of contralateral SD strip, grid, and depth electrodes are previously unreported techniques for achieving bilateral frontal coverage in phase II monitoring in pediatric epilepsy surgery. This technique obviates the need for contralateral craniotomy and parenchymal exposure with limited, remediable risks. Larger case series using the method described herein are now necessary.

Complications of subdural and depth electrodes in 269 patients undergoing 317 procedures for invasive monitoring in epilepsy.

Intracranial monitoring is fundamental to epilepsy surgery, with reported complication rates of 3-17%. We aimed to assess the differences in complication rates between subdural and depth electrodes. We conducted a retrospective review of 317 electrode implantation procedures. All documented abnormal postoperative findings were recorded in our study. Those that resulted in a significant alteration of treatment course, including neurologic deficit, long-term medication use, reoperation, or hospital readmission, were deemed clinically significant. When possible, findings were attributed to a particular electrode type based on relative location to each electrode. Postoperative abnormalities were associated with SDE placement in 152 (47.9%) procedures and 40 (25.2%) DE placements (p < 0.001). Twenty-nine (9.1%) clinically significant complications were seen in the subdural electrode (SDE) group compared to 10 associated with DEs (6.3%, p = 0.37). SDEs were associated with increased rates of any postoperative hemorrhage (p < 0.001) or extraaxial collection (p = 0.007). Subdural grid placement was associated with an increased risk of any extraaxial collection (odds ratio [OR 2.42), as well as clinically significant collections (OR 9.47). Previous craniotomy was found to be associated with any abnormal postoperative finding (OR 1.71) as well as radiographic hemorrhage (OR 1.99). Concurrent resection is also associated with abnormal findings (OR 1.83) and extraaxial collections (OR 2.37). The overall complication rate was 9.1%, with 13 procedures (4.1%) resulting in neurologic deficit. However, only two patients (0.6%) had permanent neurologic sequelae resulting from lead placement. Subdural electrodes appear to have an increased rate of abnormal postoperative findings, including hemorrhage and extraaxial collections; however, there was no difference in clinically significant findings. Subdural grids also appear to be associated with symptomatic extraaxial collections, and previous craniotomy increases the risk of hemorrhage. Overall, intracranial monitoring remains a safe and effective procedure for localization of operative seizure foci. Patient selection and risk education for various modalities is an essential aspect of preoperative evaluation.

A novel miniature robotic device for frameless implantation of depth electrodes in refractory epilepsy.

OBJECTIVE The authors' group recently published a novel technique for a navigation-guided frameless stereotactic approach for the placement of depth electrodes in epilepsy patients. To improve the accuracy of the trajectory and enhance the procedural workflow, the authors implemented the iSys1 miniature robotic device in the present study into this routine. METHODS As a first step, a preclinical phantom study was performed using a human skull model, and the accuracy and timing between 5 electrodes implanted with the manual technique and 5 with the aid of the robot were compared. After this phantom study showed an increased accuracy with robot-assisted electrode placement and confirmed the robot's ability to maintain stability despite the rotational forces and the leverage effect from drilling and screwing, patients were enrolled and analyzed for robot-assisted depth electrode placement at the authors' institution from January 2014 to December 2015. All procedures were performed with the S7 Surgical Navigation System with Synergy Cranial software and the iSys1 miniature robotic device. RESULTS Ninety-three electrodes were implanted in 16 patients (median age 33 years, range 3-55 years; 9 females, 7 males). The authors saw a significant increase in accuracy compared with their manual technique, with a median deviation from the planned entry and target points of 1.3 mm (range 0.1-3.4 mm) and 1.5 mm (range 0.3-6.7 mm), respectively. For the last 5 patients (31 electrodes) of this series the authors modified their technique in placing a guide for implantation of depth electrodes (GIDE) on the bone and saw a significant further increase in the accuracy at the entry point to 1.18 ± 0.5 mm (mean ± SD) compared with 1.54 ± 0.8 mm for the first 11 patients (p = 0.021). The median length of the trajectories was 45.4 mm (range 19-102.6 mm). The mean duration of depth electrode placement from the start of trajectory alignment to fixation of the electrode was 15.7 minutes (range 8.5-26.6 minutes), which was significantly faster than with the manual technique. In 12 patients, depth electrode placement was combined with subdural electrode placement. The procedure was well tolerated in all patients. The authors did not encounter any case of hemorrhage or neurological deficit related to the electrode placement. In 1 patient with a psoriasis vulgaris, a superficial wound infection was encountered. Adequate physiological recordings were obtained from all electrodes. No additional electrodes had to be implanted because of misplacement. CONCLUSIONS The iSys1 robotic device is a versatile and easy to use tool for frameless implantation of depth electrodes for the treatment of epilepsy. It increased the accuracy of the authors' manual technique by 60% at the entry point and over 30% at the target. It further enhanced and expedited the authors' procedural workflow.

Spreading depolarizations in patients with spontaneous intracerebral hemorrhage: Association with perihematomal edema progression

Pathophysiologic mechanisms of secondary brain injury after intracerebral hemorrhage and in particular mechanisms of perihematomal-edema progression remain incompletely understood. Recently, the role of spreading depolarizations in secondary brain injury was established in ischemic stroke, subarachnoid hemorrhage and traumatic brain injury patients. Its role in intracerebral hemorrhage patients and in particular the association with perihematomal-edema is not known. A total of 27 comatose intracerebral hemorrhage patients in whom hematoma evacuation and subdural electrocorticography was performed were studied prospectively. Hematoma evacuation and subdural strip electrode placement was performed within the first 24 h in 18 patients (67%). Electrocorticography recordings started 3 h after surgery (IQR, 3–5 h) and lasted 157 h (median) per patient and 4876 h in all 27 patients. In 18 patients (67%), a total of 650 spreading depolarizations were observed. Spreading depolarizations were more common in the initial days with a peak incidence on day 2. Median electrocorticography depression time was longer than previously reported (14.7 min, IQR, 9–22 min). Postoperative perihematomal-edema progression (85% of patients) was significantly associated with occurrence of isolated and clustered spreading depolarizations. Monitoring of spreading depolarizations may help to better understand pathophysiologic mechanisms of secondary insults after intracerebral hemorrhage. Whether they may serve as target in the treatment of intracerebral hemorrhage deserves further research.