Magnetoencephalography (MEG) predicts focal epileptogenicity in cavernomas

Perifocal edema is a risk factor for preoperative seizures in patients with meningioma WHO grade 2 and 3

BACKGROUND

Patients with intracranial meningiomas frequently suffer from tumor-related seizures prior to resection, impacting patients' quality of life. We aimed to elaborate on incidence and predictors for seizures in a patient cohort with meningiomas WHO grade 2 and 3.

METHODS

We retrospectively searched for patients with meningioma WHO grade 2 and 3 according to the 2021 WHO classification undergoing tumor resection. Clinical, histopathological and imaging findings were collected and correlated with preoperative seizure development. Tumor and edema volumes were quantified.

RESULTS

Ninety-five patients with a mean age of 59.5 ± 16.0 years were included. Most tumors (86/95, 90.5%) were classified as atypical meningioma WHO grade 2. Nine of 95 tumors (9.5%) corresponded to anaplastic meningiomas WHO grade 3, including six patients harboring TERT promoter mutations. Meningiomas were most frequently located at the convexity in 38/95 patients (40.0%). Twenty-eight of 95 patients (29.5%) experienced preoperative seizures. Peritumoral edema was detected in 62/95 patients (65.3%) with a median volume of 9 cm3 (IR: 0-54 cm3). Presence of peritumoral edema but not age, tumor localization, TERT promoter mutation, brain invasion or WHO grading was associated with incidence of preoperative seizures, as confirmed in multivariate analysis (OR: 6.61, 95% CI: 1.18, 58.12, p = *0.049). Postoperative freedom of seizures was achieved in 91/95 patients (95.8%).

CONCLUSIONS

Preoperative seizures were frequently encountered in about every third patient with meningioma WHO grade 2 or 3. Patients presenting with peritumoral edema on preoperative imaging are at particular risk for developing tumor-related seizures. Tumor resection was highly effective in achieving seizure freedom.

Practical Fundamentals of Clinical MEG Interpretation in Epilepsy

Magnetoencephalography (MEG) is a neurophysiologic test that offers a functional localization of epileptic sources in patients considered for epilepsy surgery. The understanding of clinical MEG concepts, and the interpretation of these clinical studies, are very involving processes that demand both clinical and procedural expertise. One of the major obstacles in acquiring necessary proficiency is the scarcity of fundamental clinical literature. To fill this knowledge gap, this review aims to explain the basic practical concepts of clinical MEG relevant to epilepsy with an emphasis on single equivalent dipole (sECD), which is one the most clinically validated and ubiquitously used source localization method, and illustrate and explain the regional topology and source dynamics relevant for clinical interpretation of MEG-EEG.

The 10 Common Evidence-Supported Indications for MEG in Epilepsy Surgery: An Illustrated Compendium

Unfamiliarity with the indications for and benefits of magnetoencephalography (MEG) persists, even in the epilepsy community, and hinders its acceptance to clinical practice, despite the evidence. The wide treatment gap for patients with drug-resistant epilepsy and immense underutilization of epilepsy surgery had similar effects. Thus, educating referring physicians (epileptologists, neurologists, and neurosurgeons) both about the value of epilepsy surgery and about the potential benefits of MEG can achieve synergy and greatly improve the process of selecting surgical candidates. As a practical step toward a comprehensive educational process to benefit potential MEG users, current MEG referrers, and newcomers to MEG, the authors have elected to provide an illustrated guide to 10 everyday situations where MEG can help in the evaluation of people with drug-resistant epilepsy. They are as follows: (1) lacking or imprecise hypothesis regarding a seizure onset; (2) negative MRI with a mesial temporal onset suspected; (3) multiple lesions on MRI; (4) large lesion on MRI; (5) diagnostic or therapeutic reoperation; (6) ambiguous EEG findings suggestive of "bilateral" or "generalized" pattern; (7) intrasylvian onset suspected; (8) interhemispheric onset suspected; (9) insular onset suspected; and (10) negative (i.e., spikeless) EEG. Only their practical implementation and furtherance of personal and collective education will lead to the potentially impactful synergy of the two-MEG and epilepsy surgery. Thus, while fulfilling our mission as physicians, we must not forget that ignoring the wealth of evidence about the vast underutilization of epilepsy surgery - and about the usefulness and value of MEG in selecting surgical candidates - is far from benign neglect.

Evidence for the Role of Magnetic Source Imaging in the Presurgical Evaluation of Refractory Epilepsy Patients

Magnetoencephalography (MEG) in the field of epilepsy has multiple advantages; just like electroencephalography (EEG), MEG is able to measure the epilepsy specific information (i.e., the brain activity reflecting seizures and/or interictal epileptiform discharges) directly, non-invasively and with a very high temporal resolution (millisecond-range). In addition MEG has a unique sensitivity for tangential sources, resulting in a full picture of the brain activity when combined with EEG. It accurately allows to perform source imaging of focal epileptic activity and functional cortex and shows a specific high sensitivity for a source in the neocortex. In this paper the current evidence and practice for using magnetic source imaging of focal interictal and ictal epileptic activity during the presurgical evaluation of drug resistant patients is being reviewed.

Challenges in the pharmacological management of epilepsy and its causes in the elderly

Epilepsy represents the third most common neurological disorders in the elderly after cerebrovascular disorders and dementias. The incidence of new-onset epilepsy peaks in this age group. The most peculiar aetiologies of late-onset epilepsy are stroke, dementia, and brain tumours. However, aetiology remains unknown in about half of the patients. Diagnosis of epilepsy may be challenging due to the frequent absence of ocular witnesses and the high prevalence of seizure-mimics (i.e. transient ischemic attacks, syncope, transient global amnesia or vertigo) in the elderly. The diagnostic difficulties are even greater when patients have cognitive impairment or cardiac diseases. The management of late-onset epilepsy deserves special considerations. The elderly can reach seizure control with low antiepileptic drugs (AEDs) doses, and seizure-freedom is possible in the vast majority of patients. Pharmacological management should take into account pharmacokinetics and pharmacodynamics of AEDs and the frequent occurrence of comorbidities and polytherapy in this age group. Evidences from double-blind and open-label studies indicate lamotrigine, levetiracetam and controlled-release carbamazepine as first line treatment in late-onset epilepsy.

Normotopic cortex is the major contributor to epilepsy in experimental double cortex

OBJECTIVE

Subcortical band heterotopia (SBH) is a cortical malformation formed when neocortical neurons prematurely stop their migration in the white matter, forming a heterotopic band below the normotopic cortex, and is generally associated with intractable epilepsy. Although it is clear that the band heterotopia and the overlying cortex both contribute to creating an abnormal circuit prone to generate epileptic discharges, it is less understood which part of this circuitry is the most critical. Here, we sought to identify the origin of epileptiform activity in a targeted genetic model of SBH in rats.

METHODS

Rats with SBH (Dcx-KD rats) were generated by knocking down the Dcx gene using shRNA vectors transfected into neocortical progenitors of rat embryos. Origin, spatial extent, and laminar profile of bicuculline-induced interictal-like activity on neocortical slices were analyzed by using extracellular recordings from 60-channel microelectrode arrays. Susceptibility to pentylenetetrazole-induced seizures was assessed by electrocorticography in head-restrained nonanesthetized rats.

RESULTS

We show that the band heterotopia does not constitute a primary origin for interictal-like epileptiform activity in vitro and is dispensable for generating induced seizures in vivo. Furthermore, we report that most interictal-like discharges originating in the overlying cortex secondarily propagate to the band heterotopia. Importantly, we found that in vivo suppression of neuronal excitability in SBH does not alter the higher propensity of Dcx-KD rats to display seizures.

INTERPRETATION

These results suggest a major role of the normotopic cortex over the band heterotopia in generating interictal epileptiform activity and seizures in brains with SBH.

The outlook for adults with epileptic seizure(s) associated with cerebral cavernous malformations or arteriovenous malformations

Cerebral cavernous malformations (CCMs) and arteriovenous malformations (AVMs) are common: their asymptomatic prevalence on brain magnetic resonance imaging (MRI) is 1 in 625 and 1 in 2,000, respectively. The risk of epileptic seizure(s) for people with AVMs and CCMs affects their domestic, social, and professional lives, and may influence their decisions about treatment. This article summarizes the seizure risks for people with AVMs and CCMs, gleaned from published original articles indexed in OVID Medline and Embase before 1 January 2012. In the absence of prior intracranial hemorrhage and nonhemorrhagic focal neurologic deficit, a population-based study in Scotland, United Kingdom, found that the 5-year risks of first seizure were 8% for AVM and 4% for CCM; presentation with intracranial hemorrhage or focal neurologic deficit raised this risk for AVM (23%) but not for CCM (6%). Features associated with the occurrence of epileptic seizures for CCM are lesion multiplicity and cortical CCM location, whereas for AVM the most consistently reported associations are younger age, temporal location, cortical involvement, and nidus diameter >3 cm. In the absence of prior intracranial hemorrhage and nonhemorrhagic focal neurologic deficit, the 5-year risk of developing epilepsy following a first seizure is 58% for AVM and 94% for CCM, though there is no difference in the chance of achieving 2-year seizure freedom in this time frame (45% AVM vs. 47% CCM). Observational case series describe encouraging differences in seizure frequency before and after AVM and CCM treatment, but the shortage of studies demonstrating dramatic effects in comparison to concurrent control groups justifies the need for more controlled studies, ideally with randomized treatment allocation when the benefits of AVM or CCM treatment are uncertain.

Predictive value of electrocorticography for postoperative epilepsy in patients with supratentorial meningioma

This study examines electrocorticography (ECoG) signals in patients with supratentorial meningioma before and after tumor resection, and discusses its predictive value with regard to postoperative epilepsy. Ninety-one patients with supratentorial meningioma, who presented with seizures, were studied. Patients were followed-up for 2 to 5 years, and the occurrence rate of postoperative epilepsy in each group was compared. Depending on the frequency and amplitude variation in multiple spike waves on ECoG, patients were divided into those with an increase in epileptic discharge (Group A), those with no change (Group B), and those with a reduction in epileptic discharge (Group C). Postoperative seizures was classified as early postoperative seizures (within 1 week of surgery) or late postoperative seizures (> 1 week after surgery). After lesion resection and measurement of ECoG, the 91 patients were divided into Group A (12 patients, 13.19%), Group B (36 patients, 39.56%) and Group C (43 patients, 47.25%). Of these 91 patients, 29 (31.87%) had early postoperative seizures of which seven patients (58.33%) were from Group A, 13 (36.11%) were from Group B and nine (20.93%) were from Group C (χ(2)=6.53, p<0.05). Seventeen patients (18.68%) had late postoperative seizures, of which two patients (16.67%) were from Group A, seven were from Group B (19.44%) and eight were from Group C (18.60%) (χ(2)=0.05, p>0.05). Of the 29 patients with early postoperative seizures, seven (24.14%) also had late postoperative epilepsy. Of the 62 patients who did not experience early postoperative seizures, 10 (16.13%) also had late postoperative epilepsy (χ(2)=0.83, p>0.05). Thus, the change in ECoG before and after resection in patients with supratentorial meningioma has a predictive value for early postoperative seizures.

Cliniconeuropathologic correlations show astroglial albumin storage as a common factor in epileptogenic vascular lesions

PURPOSE

Intracerebral vascular malformations including cavernous angiomas (CAs) and arteriovenous malformations (AVMs) are an important cause of chronic pharmacoresistant epilepsies. Little is known about the pathogenetic basis of epilepsy in patients with vascular malformations. Intracerebral deposits of iron-containing blood products have been generally regarded as responsible for the strong epileptogenic potential of CAs. Here, we have analyzed whether blood-brain barrier (BBB) dysfunction and subsequent astrocytic albumin uptake, recently described as critical trigger of focal epilepsy, represent pathogenetic factors in vascular lesion-associated epileptogenesis.

METHODS

We examined the correlation between hemosiderin deposits, albumin accumulation, and several clinical characteristics in a series of 80 drug-refractory epilepsy patients with CAs or AVMs who underwent surgical resection. Analysis of clinical parameters included gender, age of seizure onset, epilepsy frequency, duration of epilepsy before surgery, and postoperative seizure outcome classification according to Engel class scale. Hemosiderin deposits in the adjacent brain tissue of the vascular lesion were semiquantitatively analyzed. Fluorescent double-immunohistochemistry using GFAP/albumin costaining was performed to study albumin extravasation.

KEY FINDINGS

Our results suggest that a shorter duration of preoperative epilepsy is correlated with significantly better postsurgical outcome (p < 0.05), whereas no additional clinical or neuropathologic parameter correlated significantly with the postsurgical seizure situation. Intriguingly, we observed strong albumin immunoreactivity within the vascular lesion and in perilesional astrocytes (57.65 ± 4.05%), but not in different control groups.

SIGNIFICANCE

Our present data on albumin uptake in brain tissue adjacent to AVMs and CAs suggests BBB dysfunction and accumulation of albumin within astrocytes as a new pathologic feature potentially associated with the epileptogenic mechanism for vascular lesions and provides novel therapy perspectives for antiepileptogenesis in affected patients.

Surgical management of cavernous malformations presenting with drug-resistant epilepsy

Cerebral cavernous malformations (CMs) are dynamic lesions characterized by continuous size changes and repeated bleeding. When involving cortical tissue, CMs pose a significant risk for the development of drug-resistant epilepsy, which is thought to be result of an altered neuronal network caused by the lesion itself and its blood degradation products. Preoperative evaluation should comprise a complete seizure history, neurological examination, epilepsy-oriented MRI, EEG, video-EEG, completed with SPECT, PET, functional MRI, and/or invasive monitoring as needed. Radiosurgery shows variable rates of seizure freedom and a high incidence of complications, thus microsurgical resection remains the optimal treatment for CMs presenting with drug-resistant epilepsy. Two thirds of patients reach Engel I class at 3-year follow-up, regardless of lobar location. Those with secondarily generalized seizures, a higher seizure frequency, and generalized abnormalities on preoperative or postoperative EEG, show poorer outcomes, while factors such as gender, duration of epilepsy, lesion size, age, bleeding at the time of surgery, do not correlate consistently with seizure outcome. Electrocorticography and a meticulous removal of all cortical hemosiderin - beyond pure lesionectomy - reduce the risk of symptomatic recurrences.

The role of magnetoencephalography in children undergoing hemispherectomy

OBJECT

Hemispherectomy is an established neurosurgical procedure for medication-resistant epilepsy in children. Despite the effectiveness of this technique, there are patients who do not achieve an optimum outcome after surgery; possible causes of suboptimal results include the presence of bilateral independent epileptogenic foci. Magnetoencephalography (MEG) is an emerging tool that has been found to be useful in the management of lesional and nonlesional epilepsy. The authors analyzed the relative contribution of MEG in patient selection for hemispherectomy.

METHODS

The medical records of children undergoing hemispherectomy at the Hospital for Sick Children were reviewed. Those patients who underwent MEG as part of the presurgical evaluation were selected.

RESULTS

Thirteen patients were included in the study. Nine patients were boys. The mean age at the time of surgery was 66 months (range 10-149 months). Seizure etiology was Rasmussen encephalitis in 6 patients, hemimegalencephaly in 2 patients, and cortical dysplasia in 4 patients. In 8 patients, video-EEG and MEG results were consistent to localize the primary epileptogenic hemisphere. In 2 patients, video-EEG lateralized the ictal onset, but MEG showed bilateral spikes. Two patients had bilateral video-EEG and MEG spikes. Engel Class I, II, and IV outcomes were seen in 10, 2, and 1 patients, respectively. In 2 of the patients who had an outcome other than Engel Class I, the MEG clusters were concentrated in the disconnected hemisphere. The third patient had bilateral clusters and potentially independent epileptogenic foci from bilateral cortical dysplasia.

CONCLUSIONS

The presence of unilateral MEG spike waves correlated with good outcomes following hemispherectomy. In some cases, MEG provides information that differs from that obtained from video-EEG and conventional MR imaging studies. Further studies with a greater number of patients are needed to assess the role of MEG in the preoperative assessment of candidates for hemispherectomy.

Low proliferation and differentiation capacities of adult hippocampal stem cells correlate with memory dysfunction in humans

The hippocampal dentate gyrus maintains its capacity to generate new neurons throughout life. In animal models, hippocampal neurogenesis is increased by cognitive tasks, and experimental ablation of neurogenesis disrupts specific modalities of learning and memory. In humans, the impact of neurogenesis on cognition remains unclear. Here, we assessed the neurogenic potential in the human hippocampal dentate gyrus by isolating adult human neural stem cells from 23 surgical en bloc hippocampus resections. After proliferation of the progenitor cell pool in vitro we identified two distinct patterns. Adult human neural stem cells with a high proliferation capacity were obtained in 11 patients. Most of the cells in the high proliferation capacity cultures were capable of neuronal differentiation (53 ± 13% of in vitro cell population). A low proliferation capacity was observed in 12 specimens, and only few cells differentiated into neurons (4 ± 2%). This was reflected by reduced numbers of proliferating cells in vivo as well as granule cells immunoreactive for doublecortin, brain-derived neurotrophic factor and cyclin-dependent kinase 5 in the low proliferation capacity group. High and low proliferation capacity groups differed dramatically in declarative memory tasks. Patients with high proliferation capacity stem cells had a normal memory performance prior to epilepsy surgery, while patients with low proliferation capacity stem cells showed severe learning and memory impairment. Histopathological examination revealed a highly significant correlation between granule cell loss in the dentate gyrus and the same patient's regenerative capacity in vitro (r = 0.813; P < 0.001; linear regression: R²(adjusted) = 0.635), as well as the same patient's ability to store and recall new memories (r = 0.966; P = 0.001; linear regression: R²(adjusted) = 0.9). Our results suggest that encoding new memories is related to the regenerative capacity of the hippocampus in the human brain.

Interactions between antiepileptic and chemotherapeutic drugs in children with brain tumors: is it time to change treatment?

Epileptic seizures are a common clinical problem in children with brain tumors. The conventional antiepileptic drugs (AEDs) permit a good seizure control in most of these children. An emerging problem is the possible interactions between AEDs and chemotherapeutic drugs, because many of these drugs are metabolized by the cytochrome P450. The aim of this article is to propose a novel therapeutic approach for new-onset epilepsy in children with brain tumors. Among the new AEDs not metabolized by the P450 system, levetiracetam seems to be a promising AED owing to its pharmacokinetic features, efficacy, and safety.

LONG-TERM OUTCOME OF PATIENTS WITH MULTIPLE CEREBRAL CAVERNOUS MALFORMATIONS

OBJECTIVE

Multiple cerebral cavernous malformations (MCCMs) typically occur in patients with a family history of these lesions. Literature on MCCMs is scarce, and little is known about their natural history.

METHODS

Of 264 consecutive patients with cerebral cavernomas treated at the Department of Neurosurgery, Helsinki University Central Hospital, in the past 27 years, 33 patients had MCCMs. Lesions were categorized according to the Zabramski classification scale. Follow-up questionnaires were sent to all patients. Outcome was assessed using the Glasgow Outcome Scale, and amelioration of epilepsy was assessed using the Engel scale. All clinical data were analyzed retrospectively.

RESULTS

The mean age of patients at diagnosis was 44 years. Sex presentation was almost equal. Nine percent of all patients had a family history of the disease. Patients presented with epilepsy, acute headache, and focal neurological deficits. MCCMs were incidental findings in 2 patients. Altogether, 416 cavernomas were found: 70% supratentorial and 30% infratentorial. Fifteen patients had symptomatic hemorrhage before admission to our department. Surgery was performed on 18 patients. In most cases, the largest cavernoma was removed. Postoperatively, 1 patient experienced temporary hemiparesis, and another developed permanent motor dysphasia. No mortalities occurred. The mean follow-up time was 7.7 years. Twenty-six patients (79%) were in good condition. Among patients with epilepsy who underwent lesionectomy, 70% had an Engel class I outcome. On follow-up magnetic resonance imaging, 52 de novo cavernomas were found.

CONCLUSION

Surgical treatment of patients with MCCMs is safe. An extirpation of the clinically active cavernoma prevents further bleedings and improves outcome of epilepsy.

Neuromagnetic Localization of Spike Sources in Perilesional, Contralateral Mirror, and Ipsilateral Remote Areas in Patients with Cavernoma

PURPOSE

To assess neuromagnetic spike localization as an indication for extended lesionectomy of cavernoma.

METHODS

Electroencephalography (EEG) and magnetoencephalography (MEG) was simultaneously recorded in 17 patients (8 men, mean age 29.7 years) with single cavernoma. The location of the equivalent current dipole (ECD) of the interictal spikes was correlated with the lesion shown by magnetic resonance imaging.

RESULTS

Preoperative ECD localization was classified into four types: perilesional, adjacent to the cavernoma only (n = 6); mirror, adjacent to the lesion and at the contralateral homologous site (n = 5); remote, mainly at a remote site in the ipsilateral hemisphere (n = 3); and no spikes (n = 3). The spikes were detected by only MEG in two of five "mirror" and all three "remote" patients. In the mirror group, contralateral spikes were synchronized with the ipsilateral spikes, or also occurred independently. Two "perilesional" and two "mirror" patients became seizure-free and spike-free after extended lesionectomy. In contrast, the other two "mirror" patients had residual seizures and spikes after pure lesionectomy.

CONCLUSION

The detectability of mirror and remote spikes was higher by MEG than by EEG, whereas the detectability of perilesional spikes was similar by MEG and EEG. Therefore, the use of both EEG and MEG will provide the maximum information about spike distribution and propagation. Residual seizures and spikes after pure lesionectomy, but not after extended lesionectomy, in the "mirror" patients suggest the importance of resection of the perilesional irritable zone. Extended resection of the irritable cortex surrounding cavernoma is recommended for better seizure control, particularly in "mirror" patients.

Utility of Magnetoencephalography in the Evaluation of Recurrent Seizures after Epilepsy Surgery

PURPOSE

To study the role of magnetoencephalography (MEG) in the surgical evaluation of children with recurrent seizures after epilepsy surgery.

METHODS

We studied 17 children with recurrent seizures after epilepsy surgery using interictal and ictal scalp EEG, intracranial video EEG (IVEEG), MRI, and MEG. We analyzed the location and distribution of MEG spike sources (MEGSSs) and the relationship of MEGSSs to the margins of previous resections and surgical outcome.

RESULTS

Clustered MEGSSs occurred at the margins of previous resections within two contiguous gyri in 10 patients (group A), extended spatially from a margin by < or =3 cm in three patients (group B), and were remote from a resection margin by >3 cm in six patients (group C). Two patients had concomitant group A and C clusters. Thirteen patients underwent second surgeries. IVEEG was used in four patients. Six of seven patients with group A MEGSS clusters did not require IVEEG for second surgeries. Follow-up periods ranged from 0.6 to 4.3 years (mean: 2.6 years). Eleven children, including eight who became seizure-free, achieved Engel class I or II.

CONCLUSION

Our data demonstrate the utility of MEG for evaluating patients with recurrent seizures after epilepsy surgery. Specific MEGSS cluster patterns delineate epileptogenic zones. Removing cluster regions adjacent to the margins of previous resections, in addition to removing recurrent lesions, achieves favorable surgical outcome. Cluster location and extent identify which patients require IVEEG, potentially eliminating IVEEG for some. Patients with remotely located clusters require IVEEG for accurate assessment and localization of the entire epileptogenic zone.

Electrocorticography discharge patterns in patients with a cavernous hemangioma and pharmacoresistent epilepsy

OBJECT

Neurodevelopmental lesions (NDLs) such as glioneuronal tumors and cortical dysplasia produce characteristic electrocorticography (ECoG) discharge patterns. Because cavernomas, another congenital abnormality, are also associated with pharmacoresistant epilepsy, the authors wondered whether they exhibit discharge patterns similar to those occurring in NDLs.

METHODS

Intraoperative ECoG recordings from 19 patients with cavernomas and 54 with NDLs were reviewed for continuous spikes, bursts, or recruiting discharges and to determine whether these patterns were spatially coincident with the lesion. Relative densities of microglia and the intensity of Fe3+ staining in surgical samples were evaluated. Seizure outcome was assessed 1 year after surgery.

RESULTS

The mean ages at seizure onset and surgery were higher in patients in the cavernoma group than in the NDL group (22.5 and 36.4 years compared with 10.0 and 25.2 years, respectively). Neocortical discharge patterns occurred equally in patients with either cavernomas (53%) or NDLs (41%). In the mesiotemporal area coincident bursts occurred more often in patients with cavernomas than patients with NDLs (55% compared with 10%, respectively). Coincident continuous spiking was associated with a longer duration of epilepsy in patients with cavernomas (23.5 years compared with 11.4 years for those without coincident continuous spiking) and with a lower age at seizure onset in those with NDLs (4.1 years compared with 11.8 years for those without coincident continuous spiking). In the cavernoma group the absence of coincident bursts was associated with high microglia density. There were no associations between the intensity of Fe3+ staining and discharge patterns, although the discharge patterns were associated with a worse outcome in patients with NDLs.

CONCLUSIONS

In patients with NDLs, continuous spiking patterns may be markers of a widespread epileptogenic zone due to an early insult to the developing brain; in patients with cavernomas, such patterns may indicate secondary epileptogenesis. Microglia may inhibit discharge patterns in patients with cavernomas.

Multiple intracranial cavernous malformations: clinical features and treatment

BACKGROUND

Although patients with MCMs have increasingly been found in clinics, little has been focused on them. Thus, we intended to investigate these patients' clinical presentations, family history, radiological characters, and treatment strategy.

METHODS

A retrospective review of the files and family investigations were conducted for 30 patients with MCMs. All patients underwent MRI examination. Symptomatic patients underwent the surgical treatment with image-guided technique.

RESULTS

There were 19 male and 11 female patients with a total 79 lesions. The common presentations were seizures, hemorrhages, or focal neurological deficits. Nine patients had positive or doubtful family history. The FLAIR sequence of MRI showed the highest sensitivity in the detection of CM lesions. In 27 symptomatic patients with 69 lesions, total removal was achieved in 19 patients with 48 lesions. In the other 8 patients with 21 lesions, 13 lesions were removed. Preoperative symptoms were improved in 21 patients and unchanged in 5. Preoperative neurological deficits temporarily worsened in one, and a new onset of seizure occurred in other one; but both gradually improved during the follow-up period. Among 3 patients with asymptomatic MCMs, one patient had hemorrhage during the follow-up period and underwent surgical operation.

CONCLUSIONS

Because a high frequency of family CM occurs in MCMs, a detailed family investigation is mandatory for each patient with MCM. Selection of higher sensitive MRI sequence would contribute to detection of more CM lesions. Microsurgery assisted with the neuroimaging techniques is the treatment of choice for symptomatic MCMs.

Use of magnetoencephalography in the presurgical evaluation of epilepsy patients

Magnetoencephalography (MEG) is used twofold for presurgical evaluation of patients with medically intractable partial epilepsy; to identify epileptogenic focus and to investigate functions of cortical areas at or near the epileptogenic focus or structural lesion. For the precise localization of the current source of epileptic discharge, the question as to whether MEG is superior to electroencephalography (EEG) is often addressed. To answer this question, so many factors, both biologically and technically related, have to be taken into consideration. The biological factors include the magnitude of epileptic discharge, its distribution over the cortex, depth of its source from the head surface, and the proportion of large pyramidal neurons tangentially oriented with respect to the head surface within the cortical area. The technical factors include the quality of the recording instrument such as the number of sensors and the use of gradiometer vs. magnetometer, the employed method of source analysis, and availability of experts in each institute. As far as the importance of ictal recording is emphasized, long-term video/EEG monitoring is of utmost importance. Thus, it is concluded that, once the epileptogenic focus is identified by the video/EEG monitoring, then MEG is superior to EEG in order to precisely localize the current source of the interictal epileptic discharge. Another question often addressed is whether MEG can replace the invasive intracranial EEG recording or not. In addition to the above-described factors, different coverage of the cortical areas by MEG vs. invasive intracranial EEG recording has to be taken into account to explain some of the recent reports related to this question. MEG can be effectively applied to the investigation of cortical functions near the epileptogenic focus. It is especially so when combined with other non-invasive studies like functional magnetic resonance imaging (fMRI). In addition to the source analysis of magnetic fields related to various events or tasks, analysis of the task-related change of rhythmic cortical oscillations is a useful tool for studying higher cortical functions such as language in the presurgical evaluation.

[Epileptogenicity and evaluation of epileptic risk]

Epilepsy is the more frequent clinical manifestation of hemispheric cavernomas in 50 to 75% of symptomatic cases; the annual risk of a first seizure is evaluated from 1.5 to 2.5%. As for all epileptogenic lesions, many questions arise: Is the pathologic tissue or the perilesional cortex responsible for the epileptic symptoms? Is the risk related with the topography of the lesion? Is the prognosis of the epilepsy related with the number of seizures? Can the epilepsy become drug-resistant? Can surgical treatment cure the epilepsy? When surgery is indicated, should lesionectomy alone or lesionectomy plus perilesional tissue resection be performed? The iron and the hemosiderin deposits induce metabolic perturbations and tissue reorganization (gliosis and sclerosis) around the cavernoma. These cortical modifications seem to be responsible for the epileptic discharges but this is difficult to demonstrate. Epileptic discharges have been recorded in the perilesional tissue in only one study of the literature. Drug therapy can usually control the seizures, but it appears that surgery is more effective when the epilepsy is recent and the seizures are not too frequent. For these reasons it would appear licit to propose the resection of the lesion when the surgical risk is not too great. In case of drug-resistant epilepsy, the same function-targeted surgical strategy may be used as for the management of any severe epilepsy.

Epilepsy in patients with brain tumours: epidemiology, mechanisms, and management

Epilepsy is common in patients with brain tumours and can substantially affect daily life, even if the tumour is under control. Several factors affect the mechanism of seizures in brain tumours, including tumour type, tumour location, and peritumoral and genetic changes. Prophylactic use of antiepileptic drugs is not recommended, and potential interactions between antiepileptic and chemotherapeutic agents persuades against the use of enzyme-inducing antiepileptic drugs. Multidrug-resistance proteins prevent the access of antiepileptic drugs into brain parenchyma, which partly explains why seizures are frequently refractory to treatment. Lamotrigine, valproic acid, and topiramate are first-line treatments of choice; if insufficient, add-on treatment with levetiracetam or gabapentin can be recommended. On the basis of clinical studies, we prefer to start treatment with valproic acid, adding levetiracetam if necessary. Risks of cognitive side-effects with antiepileptic drugs can add to previous damage by surgery or radiotherapy, and therefore appropriate choice and dose of antiepileptic drug is crucial.

Prediction of postoperative outcome with special respect to removal of hemosiderin fringe: A study in patients with cavernous haemangiomas associated with symptomatic epilepsy

PURPOSE

In this study 30 patients with symptomatic epilepsy caused by cavernomas were investigated in a postoperative follow up study to assess predictors for postoperative outcome with respect to indications, time and approach of surgery.

METHODS

Thirty patients with cavernomas refractory to medical treatment were scheduled for surgery based on the findings of high-resolution MR imaging and intensive EEG-video monitoring. Postoperative outcome of epilepsy was assessed by follow-up examinations based on the basis of classification by Engel and the International League against epilepsy (ILAE).

RESULTS

The following variables were associated with good postoperative outcome: (1) complete resection of hemosiderin fringe surrounding the cavernoma was correlated to less postoperative seizure frequency versus incomplete resection of the hemosiderin fringe according to the outcome protocol of ILAE. (2) Lower duration of epilepsy at the time of operation was correlated to a better postoperative outcome with a benefit for recovery. (3) Absence of hemorrhage before surgery and unifocal seizure onset was a predictor for a favorable outcome, whereas bilateral or multifocal seizure onset zones showed poorer postoperative outcomes. (4) In patients with dual pathology (hippocampal sclerosis in addition to a cavernoma), lesionectomy plus hippocampectomy as opposed to lesionectomy only, had a better outcome than single lesionectomy.

CONCLUSION

Postoperative outcome in patients with cavernomas should be the topic of further prospective multicenter studies involving a large number of patients. In addition to the ideal operation time and handling of dual pathology the role of extended resection including perilesional hemorrhages should be taken into account.

Spatial intralobar correlation of spike and slow wave activity localisations in focal epilepsies: A MEG analysis

12 patients with focal epilepsy were examined by magnetoencephalography (MEG). Source localisations of interictal epileptiform activity (spikes) yielded clear results. Slow wave dipole density in the frequency range from 2 to 6 Hz, using time selections from an automatic principal component analysis (PCA), was calculated. Results of spike and slow wave dipole density localisations were superimposed on MR-images of each patient. Slow wave dipole densities were increased close to spike localisations. Distances between spike center of mass and slow wave maxima were calculated, average mean distance was 2.0 cm. Independant of the localisation in either TLE or ETLE a concordance of slow wave and spike localisations were found. Slow wave localisations were found in patients with lesions in MRI and patients with no abnormalities on the MRI. In comparison to healthy subjects, slow wave dipole density in patients with epilepsy was clearly increased. The localisation of slow wave dipole density yielded additional important information and may contribute to defining the irritative zone.

Noninvasive source localization of interictal EEG spikes: effects of signal-to-noise ratio and averaging

Source localization using single current dipoles estimates equivalent centers of the spiking gray matter. The extent of the active cortex, however, is difficult to assess from scalp EEG because of the unknown individual volume conduction. The spatial scatter of dipole localizations of single spikes has been proposed as a measure of extent. Single spike localization, however, is strongly dependent on the signal-to-noise ratio (SNR), that is, the ratio of spike and background EEG amplitudes. On the other hand, averaging of all spikes yields only the localization of equivalent centers of activity. We investigated the influence of SNR and multiple subaverages on the estimation of spatial extent by comparing the localization scatter of 100 single spikes in 27 spike types of 25 epilepsy patients with 1000 different subaverages computed by random sampling and bootstrapping. Averaging increased SNR and therefore allowed for localization not only at the spike peak but also during spike onset when less cortex is active. In several subjects with known cortical lesions, the single spike scatter considerably exceeded the lesion. Single dipole scatter was highly correlated with SNR (r = -0.83, P < 0.0001) and was greatly reduced when analyzing multiple subaverages of 10, 25, 50, and 100 spikes. Thus, we found a dominant role of the SNR on the estimated extent and improvement by scatterplots based on the dipole localization of randomly sampled subaverages.

Metabolic correlates of epileptic spikes in cerebral cavernous angiomas

BACKGROUND

Cerebral cavernous angiomas (CCA) are frequently associated with focal intractable epilepsy. Epileptogenicity is usually attributed to hemosiderin deposits. Combined recording of electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) is a new method to investigate epileptic discharges.

METHODS

We used EEG-fMRI to identify BOLD responses to interictal spikes in patients with CCA. Responses were analyzed in the lesional and perilesional area, and at distance.

RESULTS

Eight patients were scanned, all with temporal lobe epilepsy and spikes. One patient had bilateral spikes, analyzed separately, and three studies with less than two spikes were excluded. All six studies analyzed showed BOLD responses. No response was found in the lesion itself or immediate periphery, and the raw fMRI signal showed signal loss in lesional and perilesional areas in all patients. Responses were close to the perilesional area in 2/6 studies. All patients showed responses at a distance from the lesions.

CONCLUSIONS

Despite susceptibility artifacts caused by iron deposits, we demonstrated EEG-fMRI responses involving the perilesional areas in 33% of studies. We also demonstrated diffuse rather than focal responses, in accordance with previous studies in lesional and non-lesional temporal lobe epilepsy, confirming the frequent distant effect of epileptic spikes.

Magnetoencephalography in Neurosurgery

OBJECTIVE:

To present applications of magnetoencephalography (MEG) in studies of neurosurgical patients.

METHODS:

MEG maps magnetic fields generated by electric currents in the brain, and allows the localization of brain areas producing evoked sensory responses and spontaneous electromagnetic activity. The identified sources can be integrated with other imaging modalities, e.g., with magnetic resonance imaging scans of individual patients with brain tumors or intractable epilepsy, or with other types of brain imaging data.

RESULTS:

MEG measurements using modern whole-scalp instruments assist in tailoring individual therapies for neurosurgical patients by producing maps of functionally irretrievable cortical areas and by identifying cortical sources of interictal and ictal epileptiform activity. The excellent time resolution of MEG enables tracking of complex spaciotemporal source patterns, helping, for example, with the separation of the epileptic pacemaker from propagated activity. The combination of noninvasive mapping of subcortical pathways by magnetic resonance imaging diffusion tensor imaging with MEG source localization will, in the near future, provide even more accurate navigational tools for preoperative planning. Other possible future applications of MEG include the noninvasive estimation of language lateralization and the follow-up of brain plasticity elicited by central or peripheral neural lesions or during the treatment of chronic pain.

CONCLUSION:

MEG is a mature technique suitable for producing preoperative “road maps” of eloquent cortical areas and for localizing epileptiform activity.

Drug-resistant temporal lobe epilepsy due to cavernous malformations

Object

Supratentorial cavernous angiomas may be associated with drug-resistant focal epilepsy. Surgical removal of the malformation may result in seizure control in a number of patients, although in most studies a long history and high frequency of attacks have been recognized as indicators of unfavorable seizure outcome. In the literature, there are no clear indications regarding the optimal diagnostic presurgical workup and the surgical strategy for this particular subgroup of patients with symptomatic epilepsy. In this paper the authors focus on the preoperative workup and the surgical management of the disease in eight consecutive patients undergoing surgery for drug-resistant temporal lobe epilepsy (TLE) due to cavernous malformations (CMs), and the relevant literature on this issue is also reviewed.

Methods

Preoperatively, all patients were assessed using a noninvasive protocol aimed at localizing the epileptogenic zone on the basis of anatomical, electrical, and clinical criteria. The presurgical assessment yielded an indication for lesionectomy in two cases, lesionectomy plus anteromesial temporal lobectomy in four cases, and lesionectomy plus extended temporal lobectomy in two cases. At follow-up examinations, seizure, neuropsychological, and psychiatric outcomes were all evaluated. Seven patients were categorized in Engel Class IA (seizure free), and one was categorized in Engel Class IB (occasional auras only). No adverse effects on neuropsychological or psychosocial functioning were observed.

Conclusions

Epilepsy surgery can be performed with excellent results in patients with intractable TLE caused by CMs. Noninvasive presurgical evaluation of these patients may enable a tailored approach, providing complete seizure relief in most cases.

Spike orientation may predict epileptogenic side across cerebral sulci containing the estimated equivalent dipole

OBJECTIVE

To evaluate whether the orientation of interictal spikes, localized in major sulci by magnetoencephalography (MEG), predicts the epileptogenic side of the sulcal wall.

METHODS

Sixteen epilepsy patients were analyzed in whom equivalent current dipoles (ECDs) of MEG spikes were localized on the central (four patients), interhemispheric (4), or sylvian fissure (8); and the epileptogenic side across the sulci had been confirmed by seizure semiology, structural lesions, or intracranial electroencephalography (EEG). ECD was classified as epileptogenic side or normal side oriented and correlated to the scalp EEG map.

RESULTS

All central (n=50) and interhemispheric (n=83) spike ECDs were oriented toward the epileptogenic side at peak latency. In scalp EEG, 91% of the spikes showed radial pattern of broad negativity above the sulcus whereas 9% showed tangential pattern with positive maximum above the epileptogenic side. Sylvian spikes were only found in patients with temporal lobe epilepsy (TLE). In sylvian spikes (n=220), 73% of ECDs were oriented toward the epileptogenic side, whereas 27% were oriented toward the normal side.

CONCLUSIONS

In central and interhemispheric spikes, epileptogenic side cortex may be gross surface negative through the sulcal wall to the adjacent gyrus. Inconsistent orientation of the sylvian spikes suggests a complex pattern of spike propagation in TLE.

SIGNIFICANCE

ECD orientation of central and interhemispheric spikes in MEG may predict the epileptogenic side.

Hirntumoren und Epilepsien

Improved tumor and epilepsy treatment requires long-term care of patients with symptomatic epilepsies caused by tumors. Pathophysiology, epidemiology, prognosis, drugs, and surgical treatment are discussed with special emphasis on seizure control, side effects, and quality of life. Because of the long-term course -- often 10 to 20 years -- optimal treatment strategies have to be selected individually. These should consider possibilities of new techniques of co-registering imaging and electrophysiology, surgery, and the interaction of anticonvulsive and chemotherapeutic drugs, cognition, and mood.