Chronic subdural cortical stimulation for phantom limb pain: report of a series of two cases.

Phantom limb pain is a complex, incompletely understood pain syndrome that is characterized by chronic painful paresthesias in a previous amputated body part. Limited treatment modalities exist that provide meaningful relief, including pharmacological treatments and spinal cord stimulation that are rarely successful for refractory cases. Here, we describe our two-patient cohort with recalcitrant upper extremity phantom limb pain treated with chronic subdural cortical stimulation. The patient with evidence of cortical reorganization and almost 60 years of debilitating phantom limb pain experienced sustained analgesic relief at a follow-up period of 6 months. The second patient became tolerant to the stimulation and his pain returned to baseline at a 1-month follow-up. Our unique case series report adds to the growing body of literature suggesting critical appraisal before widespread implementation of cortical stimulation for phantom limb pain can be considered.

Ictal onset patterns of subdural intracranial electroencephalogram in children: How helpful for predicting epilepsy surgery outcome?

AIMS: We aimed to classify ictal onset patterns (IOPs) in pediatric patients undergoing intracranial electroencephalography (IEEG) to guide surgery for refractory epilepsy. We aimed to determine if morphology of IOPs can predict surgical outcome. MATERIALS AND METHODS: We performed a retrospective review of pediatric patients who underwent epilepsy surgery guided by subdural IEEG from 2007 to 2016. IEEG seizures were reviewed by a blinded epileptologist. Data was collected on outcomes. RESULTS: Twenty-three patients with 784 seizures were included. Age at seizure onset was 0.2-11 (mean 4.3, standard deviation 3.2) years. Age at time of IEEG was 4-20 (mean 13.5, standard deviation 4.4) years. Five distinct IOPs were seen at seizure onset: A) Low voltage fast activity (LVFA) with spread to adjacent electrodes (n = 7 patients, 30%), B) Burst of LVFA followed by electrodecrement (n = 12 patients, 52%), C) Burst of rhythmic spike waves (RSW) followed by electrodecrement (n = 9 patients, 39%), D) RSW followed by LVFA (n = 7 patients, 30%), E) Rhythmic spikes alone (n = 10 patients, 43%). Twelve patients (52%) had the same IOP type with all seizures. When the area of the IOP was resected, 14 patients (61%) had Engel I outcomes. Patients who had LVFA seen within their predominant IOP type were more likely to have good surgical outcomes (odds ratio 7.50, 95% confidence interval 1.02-55.0, p = 0.05). Patients who had only one IOP type were more likely to have good outcomes than patients who had multiple IOP types (odds ratio 12.6, 95% confidence interval 1.19-134, p = 0.04). Patients who had LVFA in their predominant IOP type were older than patients who did not have LVFA (mean age 15.0 vs. 9.9 years, p = 0.02). CONCLUSIONS: LVFA at ictal onset and all seizures having the same IOP morphology are associated with increased likelihood of surgical success in children, but LVFA is less common in children who are younger at the time of IEEG.

Subdural Tension on the Brain in Patients with Chronic Subdural Hematoma Is Related to Hemiparesis but Not to Headache or Recurrence.

BACKGROUND: Hemiparesis is a major symptom of chronic subdural hematoma (CSDH). Its severity does not always correlate with hematoma size. The authors analyzed hematoma thickness, pressure, and tension to clarify the mechanism of hemiparesis in CSDH patients. METHODS: A burr-hole surgery was performed on 124 CSDHs in 102 patients. Hematoma thickness and midline shift were measured by computed tomography, and hematoma pressure was measured in surgery. According to Laplace law, tension was calculated as follows: (half the hematoma thickness × hematoma pressure)/2. Student t test and Pearson correlation coefficient (r) were applied in statistical analysis of findings. RESULTS: Motor weakness was identified in 76.5% of our cases. Tension was strongly related to hemiparesis (r = -0.747, P < 0.01), whereas hematoma thickness (r = -0.458, P < 0.01) and pressure (r = -0.596, P < 0.01) were moderately correlated. Mean age of 14 patients (13.7%) with headache was much younger than those without headache (P < 0.01). Stronger midline shift (P < 0.01) and greater ratio of midline shift to hematoma thickness (P < 0.01) were statistically correlated with headache. Recurrence was recognized in 8 patients (7.8%), and stronger midline shift (P < 0.05) and greater ratio of midline shift to hematoma thickness (P < 0.05) were statistically associated with recurrence. CONCLUSIONS: Tension is the most influencing factor to hemiparesis in CSDH patients. This study also elucidates the mechanism for quick recovery from hemiparesis after surgery in that tension on the motor cortex is decreased immediately by drainage.

Subdural grid and depth electrode monitoring in pediatric patients.

Invasive electroencephalographic monitoring with implantable subdural electrodes and intraparenchymal depth electrodes has become a basic tenet of epilepsy surgery. Improved localization of epileptic foci justifies the secondary procedure and monitoring period in many patients. Informed use of invasive monitoring in conjunction with imaging and functional studies makes epilepsy surgery a smaller, safer, and more effective endeavor. Herein we review the history, indications, implementation, and foreseeable future of grid, strip, and depth electrode use.

Visual and semiautomated evaluation of epileptogenicity in focal cortical dysplasias - An intracranial EEG study.

INTRODUCTION: The aim of the study was the evaluation of the added value of depth to subdural electrodes in delineating epileptogenicity of focal cortical dysplasias (FCDs) and to test the Epileptogenicity Index (EI) in this setting. MATERIAL AND METHODS: Fifteen patients with FCD underwent iEEG with subdural and depth electrodes. Visual/EI analysis was performed in up to three habitual seizures per patient. RESULTS: Visual analysis: Grid onset seizures (n=10) started in electrodes overlying the lesion in 7 and remote from it in 3 cases. Depth onset seizures (n=7) affected only intralesional contacts in 4, intra- and extralesional in 2, and exclusively extralesional in 1 patient. Seizures started in depth and grid contacts simultaneously in 2 cases. EI analysis: The EI completely confirmed visual localization of seizure onset in 8 cases and depicted ictal onset-time accurately in 13. Beta/gamma ictal patterns were most reliably captured. Impact on surgical decision: Resection outline differed from MRI lesion in 7 patients based on grid and in three based on depth electrode information. DISCUSSION: In FCD, seizures can be generated within gyral/deep tissue appearing normal on imaging. CONCLUSION: Investigating FCD with subdural and depth electrodes is efficient to outline the seizure onset zone. The EI is a helpful additional tool to quantify epileptogenicity. Specific ictal patterns are prerequisite for reliable results.

Placement of subdural grids in pediatric patients: technique and results.

PURPOSE: The purpose of this study is to describe common indications and technique for the application of chronic invasive electrodes in the pediatric patient suffering from medically intractable epilepsy. METHODS: This chapter was prepared based on a retrospective review of the literature and personal experience based from a large tertiary epilepsy center. CONCLUSIONS: Invasive subdural recordings are a safe and efficacious tool to identify the epileptogenic zone and its relationship to functional cortex in highly selected patients with medically refractory epilepsy. The ability to localize the EZ approaches 90 to 100 %, but seizure-free outcome is more complex depending greatly on the experience of the surgical team and the extent of resection.

Intracranial electroencephalography with subdural and/or depth electrodes in children with epilepsy: techniques, complications, and outcomes.

Intracranial electroencephalographic monitoring with subdural and/or depth electrodes is widely used for the surgical localization of epileptic foci in patients with intractable partial epilepsy; however, data on safety and surgical outcome with this technique are still inadequate. The aims of this study were to assess the morbidity of intracranial recordings and the surgical outcomes in epileptic children. We retrospectively reviewed the clinical data for 137 children with epilepsy (mean age at implantation: 12.6 ± 3.8 years) who underwent intracranial monitoring with the implantation of strip or grid subdural electrodes and/or intracerebral depth electrodes from September 2004 to September 2011 at a tertiary epilepsy center in China. Complications were classified using five grades of severity (including mortality) and were further classified as either minor or severe. Outcome was classified according to Engel's classification. Regression analysis was performed to identify risk factors for complications. The mean duration of implantation was 5.3 ± 1.3 days. Among the 133 patients who underwent resection, 65 (48.9%) were seizure free (Engel Class I) at last known follow-up, which was >2 years after surgery for all patients. Also, 31 (23.3%) patients had a significant reduction in seizures (Engel Class II). Complications of any type were documented in 29 (21.7%) patients; 15 of these patients had intracranial hematoma. The results of multivariate analysis showed that the only independent risk factor for intracranial hematoma was number of electrode contacts. The most common pathologic diagnosis was focal cortical dysplasia (n=58). Our results showed that intracranial electroencephalographic monitoring in children provides good surgical outcomes and the level of risk is acceptable. When using this technique strategies such as using as few electrode contacts as possible should be adopted to minimize the risk of intracranial hematoma.

Localization of sleep spindles, k-complexes, and vertex waves with subdural electrodes in children.

PURPOSE: To describe for the first time in children the localization of sleep spindles, K-complexes, and vertex waves using subdural electrodes. METHODS: We enrolled children who underwent presurgical evaluation of refractory epilepsy with subdural grid electrodes. We analyzed electroencephalogram data from subdural electrodes and simultaneous recording with Cz scalp electrode. Sleep spindles, K-complexes, and vertex waves were identified and localized based on their morphology on the subdural electrodes. RESULTS: Sixteen patients (9 boys; age range, 3-18 years) were enrolled in the study. The inter-rater reliability on identification and localization of maximal amplitude was high with an intraclass correlation coefficient of 0.85 for vertex waves, 0.94 for sleep spindles, and 0.91 for K-complexes. Sleep spindles presented maximum amplitude around the perirolandic area with a field extending to the frontal regions. K-complexes presented maximum amplitude around the perirolandic area with a field extending to the frontal regions. Vertex waves presented maximum amplitude around the perirolandic areas. CONCLUSIONS: In our series of pediatric patients, sleep spindles, K-complexes, and vertex waves were localized around the perirolandic area.

Simultaneous subdural and scalp EEG correlates of frontal lobe epileptic sources.

OBJECTIVE: To assess the visibility and detectability in scalp electroencephalography (EEG) of cortical sources in frontal lobe epilepsy (FLE) as to their localization, and the extent and amplitude of activation. METHODS: We analyzed the simultaneous subdural and scalp interictal EEG recordings of 14 patients with refractory frontal lobe epilepsy (FLE) associated with focal cortical dysplasia. Subdural spike types were identified and averaged for source localization and detection of their scalp EEG correlates. Both raw and averaged scalp EEG segments were reviewed for spikes, blinded to subdural segments. We further analyzed the correlation of spike-to-background amplitude ratios in subdural and scalp EEG. RESULTS: We identified 36 spike types in subdural EEG, corresponding to 29 distinct sources. Four of 29 sources were visible by visual evaluation of scalp EEG and six additional sources were detectable after averaging: four in the medial frontal, two in the dorsolateral gyri, two in the depth of dorsolateral sulci, and two in the basal frontal region. Cortical sources generating scalp-detectable spikes presented a median of 6 cm(2) of activated cortical convexity surface and a subdural spike-to-background-amplitude ratio >8. These sources were associated with a higher number of activated subdural grid contacts and a higher subdural spike-to-background amplitude ratio than sources generating non-scalp-detectable spikes. SIGNIFICANCE: Not only dorsolateral but also basal and medial sources can be detectable in FLE. This is the first in vivo demonstration derived from simultaneous subdural and scalp EEG recordings of the complementary significance of extensive source activation and higher subdural spike-to-background amplitude ratio in the detection of cortical sources in FLE.

Dynamic mechanisms underlying afterdischarge: a human subdural recording study.

OBJECTIVE: No synoptic understanding exists of how and why afterdischarges (ADs) occur following electrical stimulation of the cerebral cortex. Based on human observations, we formulated a general mechanism for the emergence of ADs. METHODS: We retrospectively analysed spectra of AD time-series and control segments of the resting electrocorticogram (ECoG) in 15 epilepsy patients who underwent cortical stimulation mapping. The observations led to the development of phenomenological models for AD emergence and morphology. RESULTS: An analytical relationship exists between the spectrum of the baseline ECoG and the ensuing AD, characterised by 'condensation' of the main baseline spectral cluster, with variable inclusion of higher harmonics of the condensate. CONCLUSIONS: ADs arise by synchronisation of pre-existing local field potentials, likely through temporary inactivation of inhibitory interneurons from repetitive stimulation-induced depolarization. The appearance of higher harmonics indicates that ADs are further modulated by recurrent feedback, likely from the entrained activity of single units. SIGNIFICANCE: For the first time, a putative mechanism is suggested for AD emergence following electrical stimulation of the cerebral cortex. Insight is also offered into several empirical observations regarding ADs, detailed in the main text. More generally, a novel conceptual synthesis emerges between the behaviour of electrically-excited cortex and the physics of nonlinearly coupled multi-oscillator systems.

Interictal estimation of intracranial seizure onset in temporal lobe epilepsy.

OBJECTIVES: To evaluate the lateralizing and localizing values of interictal focal slow activity (IFSA), single pulse electrical stimulation (SPES) and (18)FDG PET, in order to estimate their potential to complement ictal intracranial recordings and reduce prolonged monitoring in patients with temporal lobe epilepsy. METHODS: The study includes 30 consecutive patients with bilateral temporal subdural electrodes and focal seizure onset. IFSA, SPES and (18)FDG PET when available, were visually assessed and their combined lateralization was based on the majority of the individual lateralizing tests. RESULTS: In the 18 patients who had all three tests, lateralization was congruent with seizure onset areas in 15 (83%). When lateralized (15 patients), (18)FDG PET was always congruent with intracranial seizure onset. In all 12 patients without (18)FDG PET, lateralization combining IFSA and SPES was congruent with seizure onset, including two with bilateral independent seizure onset on subdural monitoring. 22 out of the 23 patients who had surgery enjoyed favorable outcome (Engel I or II). CONCLUSION: Intracranial IFSA and SPES can reliably predict the side and site (mesial versus lateral temporal) of seizure onset when they lateralize to the same side. SIGNIFICANCE: (18)FDG PET can be useful in planning electrode implantation. During intracranial recordings, IFSA and SPES have the potential to reduce telemetry time, risks and costs.

Subdural to subgaleal EEG signal transmission: the role of distance, leakage and insulating affectors.

OBJECTIVE: To estimate the area of cortex affecting the extracranial EEG signal. METHODS: The coherence between intra- and extracranial EEG channels were evaluated on at least 10 min of spontaneous, awake data from seven patients admitted for epilepsy surgery work up. RESULTS: Cortical electrodes showed significant extracranial coherent signals in an area of approximately 150 cm(2) although the field of vision was probably only 31 cm(2) based on spatial averaging of intracranial channels taking into account the influence of the craniotomy and the silastic membrane of intracranial grids. Selecting the best cortical channels, it was possible to increase the coherence values compared to the single intracranial channel with highest coherence. The coherence seemed to increase linearly with an accumulation area up to 31 cm(2), where 50% of the maximal coherence was obtained accumulating from only 2 cm(2) (corresponding to one channel), and 75% when accumulating from 16 cm(2). CONCLUSION: The skull is an all frequency spatial averager but dominantly high frequency signal attenuator. SIGNIFICANCE: An empirical assessment of the actual area of cerebral sources generating the extracranial EEG provides better opportunities for clinical electroencephalographers to determine the location of origin of particular patterns in the EEG.

Automatic 80-250Hz "ripple" high frequency oscillation detection in invasive subdural grid and strip recordings in epilepsy by a radial basis function neural network.

OBJECTIVE: Recent studies give evidence that high frequency oscillations (HFOs) in the range between 80 Hz and 500 Hz in invasive recordings of epilepsy patients have the potential to serve as reliable markers of epileptogenicity. This study presents an algorithm for automatic HFO detection. METHODS: The presented HFO detector uses a radial basis function neural network. Input features of the detector were energy, line length and instantaneous frequency. Visual marked "ripple" HFOs (80-250 Hz) of 3 patients were used to train the neural network, and a further 8 patients served for the detector evaluation. RESULTS: Detector sensitivity and specificity were 49.1% and 36.3%. The linear and rank correlation between visual and automatic marked "ripple" HFO counts over the channels were significant for all recordings. A reference detector based on the line length achieved a sensitivity of 35.4% and a specificity of 46.8%. CONCLUSIONS: Automatic detections corresponded only partly to visual markings for single events but the relative distribution of brain regions displaying "ripple" HFO activity is reflected by the automated system. SIGNIFICANCE: The detector allows the automatic evaluation of brain areas with high HFO frequency, which is of high relevance for the demarcation of the epileptogenic zone.

Chronic subdural hematoma associated with arachnoid cyst. Two case histories with pathological observations.

Arachnoid cysts are well known to induce chronic subdural hematoma (CSDH) after head injury. However, histological observations of the arachnoid cyst and hematoma membrane have only been rarely described. An 8-year-old boy and a 3-year-old boy presented with CSDH associated with arachnoid cyst. Surgical removal of the hematoma and biopsy of the hematoma membrane and cyst wall were performed. Clinical courses were good and without recurrence more than 1.5 years after surgery. Histological examination suggested that the cysts did not contribute to hematoma development. Pediatric hematoma membranes, similar to adult hematoma membranes, are key in the growth of CSDH. Therefore, simple hematoma evacuation is adequate as a first operation for CSDH associated with arachnoid cyst.

Comparison of dense array EEG with simultaneous intracranial EEG for interictal spike detection and localization.

PURPOSE: To evaluate the clinical utility of dense array electroencephalography (dEEG) for the detection yield and localization of interictal spikes in mesial temporal lobe epilepsy. METHODS: We simultaneously recorded 256-channel dEEG and intracranial electroencephalography (icEEG) implanted over the lateral and mesial temporal lobe in patients with intractable epilepsy. We calculated the dEEG spike detection rate for mesial temporal spikes which were confirmed by icEEG and applied source estimation to dEEG to compare noninvasive localization to the invasive recordings. RESULTS: 339 of 760 interictal spikes (45%) were detected by dEEG examining the 256-channel head surface array. The average icEEG amplitude of dEEG detectable spikes was 1083 µV, and that of dEEG undetectable spikes was 780 µV (P<0.05). All spikes detected in dEEG were localized to the temporal lobe. 295 of 339 spikes (87%) were well localized in mesial temporal lobe, close to the position confirmed by subdural electrodes. SIGNIFICANCE: 256-channel dEEG may provide more precise information for the localization of interictal epileptiform discharges than conventional EEG or MEG in patients with deep spike foci. 256-channel dEEG may be clinically useful in the presurgical work-up for epilepsy, providing accurate noninvasive guidance for the placement of intracranial electrodes.

The impact of subdural air collection on intraoperative motor and somatosensory evoked potentials: fact or myth?

BACKGROUND: Surgery in the semi-sitting position is susceptible to changes in motor (MEP) and somatosensory evoked potentials (SEPs), which are not related to neurological impairment. These changes have been suggested to be caused by the insulating effect of subdural air collection. This study sought to investigate the correlation of MEP and SEP final-to-baseline amplitude ratios to postoperative volumetry of frontoparietal subdural air collection. METHODS: Median nerve SEP and hand MEP findings of 47 patients operated on in the semi-sitting position were compared with 7 patients operated on in the supine position. Computed tomography was routinely performed on the 1st postoperative day in all patients, and subdural air volumetry was calculated. Final-to-baseline MEP and SEP amplitude ratios were calculated and correlated to subdural air volumetry. FINDINGS: SEP changed in 12 patients, and MEP changed in 7 patients. Postoperative subdural air collections were significantly different between the groups (semi-sitting group, mean 31.2 cm(3); supine group, mean 2 cm3; p = 0.000). For the SEP ratios, a moderate negative correlation with subdural volumetry was found in the semi-sitting group (p = 0.044). Conversely, there was no correlation in the subset of patients with SEP attenuation (p = 0.846). As concerns the MEP ratios, no correlation was demonstrated in any group (semi-sitting, p = 0.967; supine, p = 0.193). CONCLUSIONS: Although SEP amplitude reductions were associated with large subdural air collections, this was not observed in the subset of patients with SEP attenuation and for the MEP monitoring, suggesting other pathophysiological mechanisms, such as brain shift, for the artificial amplitude reduction.

Subdural EEG classification into seizure and nonseizure files using neural networks in the gamma frequency band.

This study describes a new method for offline seizure detection using intracranial EEG (iEEG). The proposed method integrated two interrelated steps: (1) establishing a decisional space on the basis of the interelectrode mean of the spectral power in the gamma frequencies after a thorough evaluation of temporal and frequency-based features and (2) constructing an artificial neural network that operated on this decisional space to delineate EEG files that contained seizures from those that did not. The data were obtained from 14 patients who underwent two-stage epilepsy surgery with subdural recordings. Of the total 157 files considered, 35 (21 interictal and 14 ictal) iEEG data files or 22% were selected randomly and used initially in a training phase. The remaining 122 iEEG data files or 78% were then used in the testing phase to assess the merits in selecting gamma power as means to detect a seizure. The results obtained exhibited an accuracy of 95.90%, a sensitivity of 92.59%, and a specificity of 96.84%. Although this method had to contend with the complex nature of iEEG and the inherent heavy computational load, the constructed artificial neural networks together with the chosen decisional space yielded the best possible outcome. The proposed method was based on aggregating the power in the 36 to 44-Hz frequency range and analyzing its behavior in time, looking for patterns indicative of seizure evolution. It was shown that the power measurement in the gamma range contains the information needed to discriminate seizure files from nonseizure files. The algorithm consisted in establishing a decision space most suitable for iEEG data classification by relying on the power spectra in the gamma frequencies and constructing and implementing an artificial neural network that generates the highest classification accuracy possible. It was noted that although only 29% (35/122) of the files were used randomly for training the detector, high measures in sensitivity, specificity, and accuracy were still achieved in the remaining files, which were subsequently used in the testing phase. Seizures are known to occur intermittently and unpredictably, and massive amounts of EEG or iEEG data need to be analyzed offline to detect seizures. This is a challenge that can only be met through reliable and time-efficient seizure-detection paradigms, an affirmation this study attempted to prove.

Using subdural electrodes to assess the safety of resections.

Subdural electrodes are frequently used to aid in the neurophysiological assessment of patients with intractable seizures. We review their use for localizing cortical regions supporting movement, sensation, and language.