Histopathological correlates of epileptogenicity as expressed by electrocorticographic spiking and seizure frequency

Post-Surgical Outcome and Its Determining Factors in Patients Operated on With Focal Cortical Dysplasia Type II-A Retrospective Monocenter Study

Purpose: Focal cortical dysplasias (FCDs) are a frequent cause of drug-resistant focal epilepsies. These lesions are in many cases amenable to epilepsy surgery. We examined 12-month and long-term post-surgical outcomes and its predictors including positive family history of epilepsy.

Methods: Twelve-month and long-term outcomes regarding seizure control after epilepsy surgery in patients operated on with FCD type II between 2002 and 2019 in the Epilepsy Center of Bonn were evaluated based on patient records and telephone interviews.

Results: Overall, 102 patients fulfilled the inclusion criteria. Seventy-one percent of patients at 12 months of follow-up (FU) and 54% of patients at the last available FU (63 ± 5.00 months, median 46.5 months) achieved complete seizure freedom (Engel class IA), and 84 and 69% of patients, respectively, displayed Engel class I outcome. From the examined variables [histopathology: FCD IIA vs. IIB, lobar lesion location: frontal vs. non-frontal, family history for epilepsy, focal to bilateral tonic–clonic seizures (FTBTCS) in case history, completeness of resection, age at epilepsy onset, age at surgery, duration of epilepsy], outcomes at 12 months were determined by interactions of age at onset, duration of epilepsy, age at surgery, extent of resection, and lesion location. Long-term post-surgical outcome was primarily influenced by the extent of resection and history of FTBTCS. Positive family history for epilepsy had a marginal influence on long-term outcomes only.

Conclusion: Resective epilepsy surgery in patients with FCD II yields very good outcomes both at 12-month and long-term follow-ups. Complete lesion resection and the absence of FTBTCS prior to surgery are associated with a better outcome.

Epileptogenic zone localization using intraoperative gamma oscillation regularity analysis in epilepsy surgery for cavernomas: patient series

BACKGROUND

In epilepsy surgery for cavernoma with intractable focal epilepsy, removal of the cavernoma with its surrounding hemosiderin deposition and other extended epileptogenic zone has been shown to improve postsurgical seizures. However, there has been no significant association between such an epileptogenic zone and intraoperative electrocorticography (ECoG) findings. The authors recently demonstrated that high regular gamma oscillation (30–70 Hz) regularity (GOR) significantly correlates with epileptogenicity.

OBSERVATIONS

The authors evaluated the utility of intraoperative GOR analysis in epilepsy surgery for cavernomas. The authors also analyzed intraoperative ECoG data from 6 patients with cavernomas. The GOR was calculated using a sample entropy algorithm. In 4 patients, the GOR was significantly high in the area with the pathological hemosiderin deposition. In 2 patients with temporal cavernoma, the GOR was significantly high in both the hippocampus and the area with the pathological hemosiderin deposition. ECoG showed no obvious epileptic waveforms in 3 patients, whereas extensive spikes were observed in 3 patients. All patients underwent cavernoma removal plus resection of the area with significantly high GOR. The 2 patients with temporal cavernomas underwent additional hippocampal transection. All patients were seizure free after surgery.

LESSONS

The high GOR may be a novel intraoperative marker of the epileptogenic zone in epilepsy surgery for cavernomas.

Repetitive miniature spikes - An underreported EEG pattern

OBJECTIVES

Low-voltage repetitive spikes are mainly described with invasive recordings and considered highly suggestive for focal cortical dysplasia (FCD). This EEG pattern has received less attention in routine scalp EEG.

METHODS

Prospective collection of EEGs with low-voltage (<50 µV) repetitive spikes (repetitive miniature spikes - RMS) between July 1982 and July 2017 at the EEG laboratory of the Medical University of Innsbruck. We analyzed patterns of RMS on routine scalp EEG recordings and examined the relationship to clinical and brain imaging data.

RESULTS

Overall, RMS were seen in 38 patients representing zero to four observations out of 5000 records per year. RMS occurred rhythmically in 14, periodically in 17 and irregularly in seven patients. The EEG pattern appeared with a frontal and central predominance. All but five patients had epilepsies; eleven patients had non-convulsive status epilepticus. Cerebral magnetic resonance imaging (cMRI) detected malformations of cortical development in eleven patients, including six patients with focal cortical dysplasias.

CONCLUSIONS

RMS are rare EEG patterns indicating focal epilepsy. Their observation on routine scalp EEGs should prompt further clinic-radiologic investigation.

SIGNIFICANCE

RMS resemble a clearly recognizable pattern in routine EEG, which is highly associated with focal epilepsy. The term is descriptive and can be added to the red flags, which can be found on routine EEG indicating underlying structural brain pathology, often in form of focal cortical dysplasia.

Presurgical intracranial investigations in epilepsy surgery

Identification and localization of the "epileptogenic process" in the brain of patients with drug-resistant epilepsy for surgical cure is the goal of presurgical investigations. Intracranial recordings are required when conflicting data between seizure clinical semiology and EEG prevent precise localization within one hemisphere or lateralization, when a visible lesion on MRI seems unrelated to the electroclinical data, or in MRI-negative cases. Two methods are currently used. The objective of the subdural grid electrocorticography with or without depth electrodes (SDG/DE) is the best possible identification of the area of onset of spontaneous seizures and localization of the eloquent cortex. The objective of stereoelectroencephalography (SEEG) is to define the epileptogenic zone (configured as a network) and its relation to an unmasked lesion. Two-dimensional (SDG) and three-dimensional (SEEG) brain sampling dictate different strategies for noninvasive presurgical phase I goals as well as for data analysis. SEEG must resolve several potential localization hypotheses in a manner that cannot be achieved with SDG. SDG operates through brain surface coverage, unlike SEEG, which samples networks. SDG estimates the extent of cortical resection through a lobar or sublobar localization of ictal onset and constraints from functional mapping. SEEG defines a tailored resection according to the results of anatomo-electro-clinical correlations in stereotaxic space that will guide the ablation of the epileptogenic zone. SEEG is currently expanding faster than SDG. The prerequisites (especially in the preimplantation hypothetical strategy) and technical tools (especially stimulation and functional mapping) in the two methods are very different. This chapter presents a comparative review of the rationale, indications, electrode implantation strategies, interpretation, and surgical decision making of these two approaches of presurgical evaluation for epilepsy surgery.

Age at epilepsy onset in patients with focal cortical dysplasias, gangliogliomas and dysembryoplastic neuroepithelial tumours

PURPOSE

The age at epilepsy onset in patients with inborn or very early acquired brain lesions depends on the epileptogenic potential of the lesion and the patients' individual "susceptibility" to epileptic seizures. To gain insight into these determinants, we analysed the case history of patients with focal cortical dysplasias (FCDs) and neuroglial tumours.

METHODS

In a systematic, retrospective analysis comprised of 233 patients who underwent surgery (116 with FCDs and 117 with neuroglial tumours), we evaluated the age at epilepsy onset according to histopathologic subgroups, lesion location and family history.

RESULTS

Epilepsy onset was significantly earlier in patients with FCD than for those with neuroglial tumours (FCDs: 8.06 ± 0.74 years, gangliogliomas: 15.86 ± 1.24 years, dysembryoplastic neuroepithelial tumours (DNTs): 19.18 ± 2.47 years; p < 0.00001). FCDs were most frequently located in the frontal, whereas neuroglial tumours most frequently in the temporal lobe. For FCD patients, the age at epilepsy onset was not dependent on lesion location, whereas DNTs in a temporal location were associated with a later epilepsy onset than gangliogliomas and extratemporal DNTs. A positive family history for epilepsy or epileptic seizures was found more frequently among patients with FCDs (FCDs: 20.4%, neuroglial tumours: 8.1%; p = 0.013).

CONCLUSION

We postulate that the age difference at epilepsy onset between patients with FCDs and neuroglial tumours can be attributed - at least partially - to unidentified genetic factors underlying the epileptogenic potential of the brain tissue. Additionally, the large variance in the age at epilepsy onset is possibly also genetically determined.

Post-resection electrocorticography has no added value in epilepsy surgery

Intra-operative electrocorticography (ECoG) has been traditionally used in the surgical management of medically refractory partial epilepsies to identify the limits of the epileptogenic zone. This retrospective study had as goal to evaluate whether tailored surgery based on the presurgical evaluation completed by intra-operative post-resection ECoG improves outcome. We reviewed 94 cases of epilepsy surgery with intra-operative ECoG and determined how many had an ECoG-guided surgical procedure in addition to the initial planned surgery. We also reviewed the presence of specific recurrent ECoG patterns of interictal epileptiform discharges (IED) in the exposed cortical surface, such as: electrographic seizures, bursts, intermittent spike waves, polyspikes or fast rhythms and continuous or quasi-continuous spiking. When performing a post-resection ECoG-tailored surgery, outcome did not improve in lesional or non-lesional epilepsy. Postoperative residual IED did not correlate with a poorer outcome. In our study, the persistence of post-resection IED on ECoG is not correlated with outcome in patients with lesional or non-lesional epilepsy.

Abnormal discharges from the temporal neocortex after selective amygdalohippocampectomy and seizure outcomes

The present study examined the relationship between residual discharges from the temporal neocortex postoperatively and seizure outcomes, in mesial temporal lobe epilepsy (MTLE) patients with hippocampal sclerosis (HS) who were treated with selective amygdalohippocampectomy (SelAH). Abnormal discharges from the temporal neocortex are often observed and remain postoperatively. However, no recommendations have been made regarding whether additional procedures to eliminate these discharges should be performed for seizure relief. We retrospectively analyzed 28 patients with unilateral MTLE and HS, who underwent transsylvian SelAH. The mean follow-up period was 29 months (range: 16-49). In the pre- and postresection states, electrocorticography (ECoG) was recorded for the temporal base and lateral temporal cortex. The extent of resection was not influenced by the results of the preresection ECoG. Even if residual abnormal discharges were identified on the temporal neocortex, no additional procedures were undertaken to eliminate these abnormalities. The postresection spike counts were examined to determine the postresective alterations in spike count, and the frequency of residual spike count. The seizure outcomes were evaluated in all patients using the Engel classification. The postoperative seizure-free rate was 92.9%. No significant correlations were seen between a decreasing spike count and seizure outcomes (p=0.9259), or between the absence of residual spikes and seizure outcomes (p=1.000). Residual spikes at the temporal neocortex do not appear to influence seizure outcomes. Only mesial temporal structures should be removed, and additional procedures to eliminate residual spikes are not required.

Surgery for focal cortical dysplasia in children using intraoperative mapping

OBJECTIVE

Children with malformation of cortical development represent a significant proportion of pediatric epilepsy surgery candidates. Here, we describe a single-center experience with pediatric patients who underwent surgery for intractable epilepsy due to focal cortical dysplasia (FCD).

METHODS

Clinical data of 78 patients under 18 years of age with diagnosis of intractable epilepsy due to FCD who underwent surgery from January 1996 to January 2012 were reviewed comparing data of patients submitted to electrocorticography (ECoG) with those without ECoG.

RESULTS

Patients' mean age at surgery was 8.52 ± 4.99 years; mean age at epilepsy onset was 2.55 ± 3.01 years. Almost 80 % of the patients underwent ECoG register that was essential for delimitation of surgical resection in 66 out of 78 patients. ECoG was performed in all patients with extratemporal lesions, and the most common FCD found was type II. Seizure outcome was similar in groups with or without ECoG.

CONCLUSIONS

Tailored resection of FCD lesions for intractable epilepsy can be safely performed in children with a good seizure outcome and low complication rate. Epilepsy surgery should be considered for all patients with FCD and refractory epilepsy.

Emerging surgical strategies of intractable frontal lobe epilepsy with cortical dysplasia in terms of extent of resection

Objective

Cortical dysplasia (CD) is one of the common causes of epilepsy surgery. However, surgical outcome still remains poor, especially with frontal lobe epilepsy (FLE), despite the advancement of neuroimaging techniques and expansion of surgical indications. The aim of this study was to focus on surgical strategies in terms of extent of resection to improve surgical outcome in the cases of FLE with CD.

Methods

A total of 11 patients of FLE were selected among 67 patients who were proven pathologically as CD, out of a total of 726 epilepsy surgery series since 1992. This study categorized surgical groups into three according to the extent of resection : 1) focal corticectomy, 2) regional corticectomy, and 3) partial functional lobectomy, based on the preoperative evaluation, in particular, ictal scalp EEG onset and/or intracranial recordings, and the lesions in high-resolution MRI. Surgical outcome was assessed following Engel's classification system.

Results

Focal corticectomy was performed in 5 patients and regional corticectomy in another set of 5 patients. Only 1 patient underwent partial functional lobectomy. Types I and II CD were detected with the same frequency (45.45% each) and postoperative outcome was fully satisfactory (91%).

Conclusion

The strategy of epilepsy surgery is to focus on the different characteristics of each individual, considering the extent of real resection, which is based on the focal ictal onset consistent with neuroimaging, especially in the practical point of view of neurosurgery.

Dysembryoplastic neuroepithelial tumors: epileptogenicity related to histologic subtypes

OBJECTIVE

To analyze the electroclinical features and the relationship between the epileptogenic zone (EZ), the tumor and focal cortical dysplasia (FCD) in the three histologic subtypes of dysembryoplastic neuroepithelial tumors (DNTs) ("simple", "complex" and "non-specific forms").

METHODS

We analyzed electroclinical data from 78 patients (50 males; 3-54 years) operated for intractable epilepsy due to a DNT. We compared EZ extent, defined by stereo-electroencephalography (n = 33), with the tumor and FCD areas, in each DNT subtype.

RESULTS

Non-specific forms (68%) and temporal location were predominant (73%). The main characteristics consisted of late childhood epilepsy onset (median 12 years), drug-resistant partial seizures and EEG abnormalities concordant with tumor location. In all DNT subtypes, intrinsic epileptogenicity was demonstrated by intralesional recordings (n = 30), displaying a depressed background activity interrupted by rapid spikes or polyspikes. EZ co-localized with the tumor in all simple and complex DNTs, but in only 1/3 of non-specific DNTs. The main discordance between the EZ and tumor extent was found in temporal non-specific DNTs associated with extensive FCD.

CONCLUSION

These results are helpful when planning surgery for DNTs.

SIGNIFICANCE

Intrinsic epileptogenicity characterizes all DNTs; however, the EZ differs according to histologic subtypes and is particularly widespread in non-specific temporal forms.

White matter abnormalities in patients with focal cortical dysplasia revealed by diffusion tensor imaging analysis in a voxelwise approach

BACKGROUND

Diffusion tensor imaging (DTI) allows the analysis of changes in microstructure, through the quantification of the spread and direction of water molecules in tissues. We used fractional anisotropy (FA) maps to compare the integrity of WM between patients and controls. The objective of the present study was to investigate WM abnormalities in patients with frontal lobe epilepsy secondary to focal cortical dysplasia (FCD).

MATERIALS AND METHODS

We included 31 controls (12 women, 33.1 ± 9.6 years, mean ± SD) and 22 patients (11 women, 30.4 ± 10.0 years), recruited from our outpatient clinic. They had clinical and EEG diagnosis of frontal lobe epilepsy, secondary to FCD detected on MRI. Patients and controls underwent 3T MRI, including the DTI sequence, obtained in 32 directions and b value of 1000 s/mm(2). To process the DTI we used the following softwares: MRIcroN and FSL/TBSS (tract-based spatial statistics). We used a threshold-free cluster enhancement with significance at p < 0.05, fully corrected for multiple comparisons across space.

RESULTS

Areas with FA reduction in patients were identified in both hemispheres, mainly in the frontal lobes, cingulum, and forceps minor (p = 0.014), caudate e anterior thalamic radiation (p = 0.034), superior longitudinal fasciculus (p = 0.044), uncinate fasciculus, and inferior fronto-occipital fasciculus (p = 0.042).

CONCLUSION

Our results showed a widespread pattern of WM microstructural abnormalities extending beyond the main lesion seen on MRI (frontal lobe), which may be related to frequent seizures or to the extent of MRI-invisible portion of FCD.

Noninvasive approach to focal cortical dysplasias: clinical, EEG, and neuroimaging features

Purpose. The main purpose is to define more accurately the epileptogenic zone (EZ) with noninvasive methods in those patients with MRI diagnosis of focal cortical dysplasia (FCD) and epilepsy who are candidates of epilepsy surgery. Methods. Twenty patients were evaluated prospectively between 2007 and 2010 with comprehensive clinical evaluation, video-electroencephalography, diffusion tensor imaging (DTI), and high-resolution EEG to localize the equivalent current dipole (ECD). Key Findings. In 11 cases with white matter asymmetries in DTI the ECDs were located next to lesion on MRI with mean distance of 14.63 millimeters with topographical correlation with the EZ. Significance. We could establish a hypothesis of EZ based on Video-EEG, high-resolution EEG, ECD method, MRI, and DTI. These results are consistent with the hypothesis that the EZ in the FCD is complex and is often larger than visible lesion in MRI.

The relationship of interictal epileptiform discharges to clinical epilepsy severity: a study of routine electroencephalograms and review of the literature

Electroencephalograms are widely used to detect interictal epileptiform discharges (IEDs) in patients with a known history of seizures. However, previous studies have not found a consistent association between the presence or frequency of IEDs and clinical epilepsy severity, possibly because of differences in subject characteristics and recording techniques. We sought to investigate this relationship in a population and setting reflective of the most common clinical usage. We analyzed electroencephalograms and clinical records of all consenting patients with a history of at least two presumed focal-onset seizures who presented for routine electroencephalograms recording over 1-year time in an academic neurophysiology laboratory (n = 129). Despite adequate statistical power, we did not find an association between the presence or absence of IEDs or IED frequency and the most recently determined seizure frequency (median, 4 per year). A higher IED incidence was seen in subjects with longer epilepsy duration (P = 0.04). Neither IED incidence nor frequency (median, 10.0 per hour) correlated with age or antiepileptic drug use. Our results differ from those of some previous studies, most of which focused on more narrow subject populations, suggesting that the patient's clinical circumstances must be taken into account before assuming the utility of IEDs on routine electroencephalography in predicting epilepsy severity.

Local and remote epileptogenicity in focal cortical dysplasias and neurodevelopmental tumours

During the pre-surgical evaluation of drug-resistant epilepsy, the assessment of the extent of the epileptogenic zone and its organization is a crucial objective. Indeed, the epileptogenic zone may be organized as a simple focal lesional site or as a more complex network (often referred to as the 'epileptogenic network') extending beyond the lesion. This distinction is particularly relevant in developmental lesions such as focal cortical dysplasias or dysembryoplastic neuroepithelial tumours and may determine both the surgical strategy and the prognosis. In this study, we have quantified the epileptogenic characteristic of brain structures explored by depth electrodes in 36 patients investigated by stereoelectroencephalography and suffering from focal drug-resistant epilepsy associated with focal cortical dysplasias or dysembryoplastic neuroepithelial tumours. This quantification was performed using the 'Epileptogenicity Index' method that accounts for both the propensity of a brain area to generate rapid discharges and the time for this area to get involved in the seizure. Epileptogenicity Index values range from 0 (no epileptogenicity) to 1 (maximal epileptogenicity). We determined Epileptogenicity Index from signals recorded in distinct brain structures including the lesional site. We studied the type of epileptogenic zone organization (focal versus network) and looked for a correlation with clinical data and post-surgical outcome. Mean Epileptogenicity Index in lesional regions was 0.87 (+/-0.25), and 0.29 (+/-0.30) in 'non-lesional' structures. The number of highly epileptogenic structures (defined by Epileptogenicity Index value >or=0.4) was 3.14 (+/-1.87) in the whole population. We found that 31% of patients had only one epileptogenic structure (N(EI>or=0.4) = 1), therefore disclosing a strictly focal epileptogenic zone organization while 25 patients had more than one epileptogenic region, disclosing a network (61%) or bilateral (8%) epileptogenic zone organization. We observed a trend for a difference in seizure outcome according to the type of epileptogenic zone organization. Indeed, 57% of patients with network organization and 87% with focal organization were seizure-free while none of those with bilateral organization became seizure-free. The determination of Epileptogenicity Index computed from electrophysiological signals recorded according to the stereoelectroencephalography technique is a novel tool. Results suggest that it can help in the delineation of the epileptogenic zone associated with brain lesions and that it could be used in the definition of the subsequent surgical resection.

The role of EEG in epilepsy: a critical review

Electroencephalography (EEG) is the most specific method to define epileptogenic cortex. Its sensitivity and specificity depend on several factors such as age and recording procedures, for example, sleep recordings and activation procedures (hyperventilation, photic stimulation). EEG reveals characteristic findings in several epilepsy syndromes. Rarely, epileptiform discharges are recorded in healthy, particularly young individuals. Ictal video/EEG recording is considered to be critical in localizing the epileptogenic zone. A careful analysis of the first clinical signs and symptoms of a seizure and of the evolution of the seizure symptomatology can provide important localizing clues. Although surface EEG recordings are less sensitive than invasive studies, they provide the best overview and, therefore, the most efficient way to define the approximate localization of the epileptogenic zone. Invasive recordings are used in patients in whom the epileptogenic zone either cannot be located with noninvasive diagnostic methods or is adjacent to eloquent cortex. The most commonly used invasive electrodes are stereotactically implanted depth electrodes and subdural strip or grid electrodes. Foramen ovale and epidural electrodes are of intermediate invasiveness, but less sensitive. Invasive electrodes are subject to sampling errors if misplaced and should be used only after exhaustive noninvasive evaluations have (1) failed to localize the epileptogenic zone and (2) led to a testable hypothesis regarding this localization. Invasive EEG studies are associated with additional risks that are justifiable only if there is a good chance of obtaining essential localizing information and on a potentially resectable area.

Different features of histopathological subtypes of pediatric focal cortical dysplasia

OBJECTIVE

Focal cortical dysplasia (FCD) is the most frequent pathological finding in pediatric epilepsy surgery patients. Several histopathological types of FCD are distinguished. The aim of the study was to define distinctive features of FCD subtypes.

METHODS

We retrospectively reviewed clinical, electroencephalographic, magnetic resonance imaging, neuropsychological, and surgical variables, and seizure outcome data in 200 children. Cortical malformations were histopathologically confirmed in all patients, including mild malformation of cortical development type II (mMCD) in 36, FCD type Ia in 55, FCD type Ib in 39, FCD type IIa in 35, and FCD type IIb in 35 subjects.

RESULTS

Perinatal risk factors were more frequent in mMCD/FCD type I than FCD type II. Children with FCD type IIb had more localized ictal electroencephalographic patterns and magnetic resonance imaging changes. Increased cortical thickness, abnormal gyral/sulcal patterns, gray/white matter junction blurring, and gray matter signal abnormality in fluid-attenuated inversion recovery and T2-weighted sequences occurred more often in FCD type II, were infrequent in FCD type I, and rare in mMCD. Lobar hypoplasia/atrophy was common in FCD type I. Hippocampal sclerosis was most frequent in FCD type I. Neuropsychological testing demonstrated no significant differences between the groups. There was a trend toward better surgical outcomes in FCD type II compared with FCD type I patients.

INTERPRETATION

Different histopathological types of mMCD/FCD have distinct clinical and imaging characteristics. The ability to predict the subtype before surgery could influence surgical planning. Invasive electroencephalographic study should be considered when mMCD/FCD type I is expected based on noninvasive tests.

Different structures involved during ictal and interictal epileptic activity in malformations of cortical development: an EEG-fMRI study

Malformations of cortical development (MCDs) are commonly complicated by intractable focal epilepsy. Epileptogenesis in these disorders is not well understood and may depend on the type of MCD. The cellular mechanisms involved in interictal and ictal events are notably different, and could be influenced independently by the type of pathology. We evaluated the relationship between interictal and ictal zones in eight patients with different types of MCD in order to better understand the generation of these activities: four had nodular heterotopia, two focal cortical dysplasia and two subcortical band heterotopia (double-cortex). We used the non-invasive EEG-fMRI technique to record simultaneously all cerebral structures with a high spatio-temporal resolution. We recorded interictal and ictal events during the same session. Ictal events were either electrical only or clinical with minimal motion. BOLD changes were found in the focal cortical dysplasia during interictal and ictal epileptiform events in the two patients with this disorder. Heterotopic and normal cortices were involved in BOLD changes during interictal and ictal events in the two patients with double cortex, but the maximum BOLD response was in the heterotopic band in both patients. Only two of the four patients with nodular heterotopia showed involvement of a nodule during interictal activity. During seizures, although BOLD changes affected the lesion in two patients, the maximum was always in the overlying cortex and never in the heterotopia. For two patients intracranial recordings were available and confirm our findings. The dysplastic cortex and the heterotopic cortex of band heterotopia were involved in interictal and seizure processes. Even if the nodular gray matter heterotopia may have the cellular substrate to produce interictal events, the often abnormal overlying cortex is more likely to be involved during the seizures. The non-invasive BOLD study of interictal and ictal events in MCD patients may help to understand the role of the lesion in epileptogenesis and also determine the potential surgical target.

Interictal regional polyspikes in noninvasive EEG suggest cortical dysplasia as etiology of focal epilepsies

PURPOSE

To evaluate the clinical significance of interictal regional polyspikes in focal epilepsies secondary to cortical dysplasia.

METHODS

We performed a data search for the term "regional polyspikes" in the database of our epilepsy-monitoring unit. Patients with generalized epilepsies including Lennox-Gastaut syndrome were excluded. Regional interictal epileptiform discharges were recorded in 513 patients with noninvasive EEG.

RESULTS

We identified 29 patients with interictal regional polyspikes and focal epilepsies. Another 484 patients showed regional epileptiform discharges other than polyspikes. The etiology of the epilepsy was significantly more frequently cortical dysplasia in the group of patients with regional polyspikes (35%, 10 of 29 patients) than in the patients with other regional epileptiform discharges (5%, 24 of 484 patients) (p < 0.01). The polyspikes were significantly more frequently localized to the extratemporal (72%; n = 21) than temporal (28%; n = 8) regions (p < 0.01). In contrast, regional epileptiform discharges other than polyspikes were significantly more frequently localized to the temporal lobe (75%; n = 362) than extratemporal regions (25%; n = 122) (p < 0.01). Eight of the 10 patients with focal cortical dysplasia had extratemporal polyspikes.

DISCUSSION

Noninvasively recorded regional polyspikes suggest cortical dysplasias as etiology of predominantly extratemporal epilepsies.

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.

Pathophysiological mechanisms of focal cortical dysplasia: a critical review of human tissue studies and animal models

Cortical dysplasia (CD, also known as malformations of cortical development) are the pathological substrates in a large percentage of patients with pharmacoresistant epilepsy who may be amenable to surgical treatment. Therefore, research on the mechanisms of dysplastic lesion formation and epileptogenicity is of paramount importance for the prevention, detection, and treatment of CD-induced epilepsy. The purpose of this review is to discuss and critically evaluate the current state and results of human tissue experimentation (focusing on reported results of studies done on neocortical dysplastic tissue resected from patients with pharmacoresistant epilepsy), and to discuss some of the concerns related to research that uses surgically resected epileptic human tissue. The use of better animal models of CD as a tool toward the better understanding of the mechanisms of pathogenesis, epileptogenesis, and epileptogenicity of dysplastic lesions will be reviewed from the perspective of their usefulness in a model of translational research that should ultimately result in better diagnostic and therapeutic techniques of CD.

Differential expression patterns of chloride transporters, Na+-K+-2Cl--cotransporter and K+-Cl--cotransporter, in epilepsy-associated malformations of cortical development

Malformations of cortical development are recognized causes of chronic medically intractable epilepsy. An increasing number of observations suggests an important role for cation-chloride co-transporters (CCTs) in controlling neuronal function. Deregulation of their expression may contribute to the mechanisms of hyperexcitability that lead to seizures. In the present study the expression and cell-specific distribution of Na+-K+-2Cl--cotransporter (NKCC1) and K+-Cl--cotransporter (KCC2) were studied immunocytochemically in different developmental lesions, including focal cortical dysplasia (FCD) type IIB (n=9), hemimegalencephaly (HMEG, n=6) and ganglioglioma (GG, n=9) from patients with medically intractable epilepsy and in age-matched controls. In normal control adult cortex, NKCC1 displayed low neuronal and glial expression levels. In contrast KCC2 showed strong and diffuse neuropil staining. Notable glial immunoreactivity (IR) was not found for KCC2. NKCC1 was highly expressed in the majority of FCD, HMEG and GG specimens. NKCC1 IR was observed in neurons of different size, including large dysplastic neurons, in balloon cells (in FCD and HMEG cases) and in glial cells with astrocytic morphology. The immunoreactivity pattern of KCC2 in FCD, HMEG and GG specimens was characterized by less neuropil staining and more intrasomatic IR compared with control. KCC2 IR was observed in neurons of different size, including large dysplastic neurons, but not in balloon cells or in glial cells with astrocytic morphology. Double-labeling experiments confirmed the differential cellular distribution of the two CCTs and their expression in GABA(A) receptor (alpha1 subunit)-positive dysplastic neurons. The cellular distribution of CCTs, with high expression of NKCC1 in dysplastic neurons and altered subcellular distribution of KCC2 resembles that of immature cortex and suggests a possible contribution of CCTs to the high epileptogenicity of malformations of cortical development.

Electrocorticographic discharge patterns in glioneuronal tumors and focal cortical dysplasia

PURPOSE

To determine whether highly epileptiform electrocorticographical discharge patterns occur in patients with glioneuronal tumors (GNTs) and focal cortical dysplasia (FCD) and whether specific histopathological features are related to such patterns.

METHODS

The series consists of operated patients with pharmacoresistant epilepsy because of FCD or GNT between 1992 and 2003. Electrocorticography was reviewed for presence of continuous spiking, bursts, recruiting discharges, or sporadic spikes. Surgical specimens were reviewed for the presence of balloon cells, (coexisting) cortical dysplasia, and relative frequencies of neurons, glia, and microglia.

RESULTS

Continuous spiking was seen in 55% versus 12% of patients with FCD and GNT, respectively (p = 0.005). Bursts and recruiting discharges were seen in a similar proportion of patients with FCD or GNT. Ninety-one percent of patients with continuous spiking showed (coexisting) cortical dysplasia in contrast to 42% of patients without this pattern (p = 0.004). The presence of balloon cells and glia or microglia content were not associated with discharge patterns.

CONCLUSION

Continuous spiking, bursts, and recruiting discharges occur in patients with FCD and GNT. Continuous spiking was seen significantly more often in patients with FCD. When continuous spiking is found with GNT, it is likely to be associated with dysplastic regions with a high neuronal density.

Seizure outcome after surgery for epilepsy due to focal cortical dysplastic lesions

Neocortical development is a highly complex process encompassing cellular proliferation, neuronal migration and cortical organization. At any time this process can be interrupted or modified by genetic or acquired factors causing malformations of cortical development (MCD). Epileptic seizures are the most common type of clinical manifestation, besides developmental delay and focal neurological deficits. Seizures due to MCD are frequently pharmacoresistant, especially those associated to focal cortical dysplasia (FCD). Surgical therapy results have been reported since 1971, however, currently available data from surgical series are still limited, mainly due to small number of patients, distinct selection of candidates and surgical strategies, variable pathological diagnosis and inadequate follow-up. This study addresses the possibilities of seizure relief following resection of focal cortical dysplasia, and the impact of presurgical evaluation, extent of resection and pathological findings on surgical outcome. We included 41 patients, 22 adults and 19 children and adolescents, with medically intractable seizures operated on from 1996 to 2002. All were submitted to standardized presurgical evaluation including high-resolution MRI, Video-EEG monitoring and ictal SPECT. Post-surgical seizure outcome was classified according to Engel's schema. Univariate and multivariate analysis were performed. Fifteen patients had temporal and 26 extratemporal epilepsies. Of the total 26 patients (63.4%) reached seizure-free status post-operatively. There was no correlation between outcome and age at surgery, duration of epilepsy, frequency of seizures, and pathological findings. There was, however, a clear correlation with topography of FCD (temporal versus extratemporal) and regional ictal EEG onset, on univariate as well as multivariate analysis.

Mcm2 labelling of balloon cells in focal cortical dysplasia

Balloon cells (BC) are the prominent and defining cellular component of type IIB Focal Cortical Dysplasia (FCD), a common cause of focal epilepsy in patients undergoing surgical treatment. BC are considered immature cells of uncommitted cellular differentiation having immunophenotypical characteristics of both neurones and glia. They are often located in the lower cortical layers and white matter underlying the dysplastic cortex, suggesting migratory arrest during development. We investigated the proliferative potential of BC in 15 cases of FCD from patients with a wide range of ages using immunohistochemistry for Mcm2 (mini chromosome maintenance protein) and Ki67. In the majority of cases, BC showed Mcm2 nuclear positivity. In addition, cells with intermediate neuronal-glial characteristics were labelled whilst the dysmorphic or hypertrophic pyramidal neuronal components of FCD were not. Ki67 labelled only occasional BC. These findings support the view that BC cells represent a pool of less differentiated glial cells with proliferative capacity which may have potential for delayed neuronal differentiation. Furthermore, as Mcm2 specifically identifies BC populations, this marker may be of diagnostic value in the subtyping of FCD lesions in patients with epilepsy.

Predictive value of electrocorticography in epilepsy patients with unilateral hippocampal sclerosis undergoing selective amygdalohippocampectomy

The purpose of this study was to evaluate the predictive value of intraoperative electro-corticography (ECoG) in patients with unilateral hippocampal sclerosis (HS) undergoing transsylvian selective amygdalohippocampectomy (sAHE). ECoG was recorded before and after resection in 22 patients with medication-resistant mesial temporal lobe epilepsy. The sAHE was performed, regardless of ECoG findings. ECoG findings recorded from the mesiobasal temporal lobe (MTL) and lateral temporal lobe (LTL) before and after the sAHE were correlated with seizure outcome 12 months later. Ten patients had right-sided and 12 left-sided HS. Average age was 37.1 years. Pre-resection spikes were restricted to the MTL in 11 patients and to the LTL in one. In three patients spikes were recorded from MTL and LTL and in seven no spikes were recorded before the resection. Fifteen patients (68%) remained completely seizure-free and 19 (86%) were in Engel's class I post-operatively. Patients with pre-resection spikes restricted to the MTL (n = 11) remained seizure-free more frequently (9/11, 82%) compared with other patients (6/11, 55%; P = 0.36). Pre-resection ECoG may be helpful in the prediction of seizure outcome in patients undergoing sAHE for mesial temporal lobe epilepsy. A larger study including more than 100 patients is needed to determine the predictive value of ECoG in patients with mesial temporal lobe epilepsy.

Electro-clinical and imaging characteristics of focal cortical dysplasia: Correlation with pathological subtypes

INTRODUCTION

Focal cortical dysplasia (CD) is a common cause of pharmaco-resistant epilepsy. CD is due to abnormalities in neuronal migration, proliferation, and/or differentiation that result in four distinct pathological subtypes: 1A, 1B, 2A, and 2B. In order to provide clinical correlation to these pathological subtypes, we reviewed the electro-clinical and imaging characteristics and surgical outcomes of the four pathological subtypes of CD.

METHODS

We retrospectively reviewed patient data from epilepsy surgeries at the Cleveland Clinic Foundation between 1990 and 2002. Only those patients with the definite pathological diagnosis of isolated cortical dysplasia were included in the study (n = 145).

RESULTS

Pathological subtypes 2A and 2B were predominantly frontal in location, and had a more severe epilepsy syndrome with lower intelligence quotient scores than subtypes 1A and 1B. Patients with subtype 1A FCD had less severe, later onset epilepsy that was predominantly located in the temporal lobe. Risk factors for epilepsy included febrile seizures for type 1A, head trauma for types 1A and 1B, and perinatal adverse events for type 2B. Type 2B demonstrated significantly more FLAIR signal abnormalities than the other groups. Sixty-three percent of patients overall had an Engel I outcome at 6 months follow-up. The best outcomes were in the 2B subtype, and in those who did not require an invasive EEG evaluation.

CONCLUSIONS

Clinically important differences exist between the pathological subtypes of CD, which may assist in their management, and provide further insight into their underlying pathophysiology.

Reflex Seizures in Patients with Malformations of Cortical Development and Refractory Epilepsy

PURPOSE

Malformations of cortical development (MCDs) are usually highly epileptogenic, and their hyperexcitability could facilitate the occurrence of reflex seizures. We sought to characterize reflex seizures in patients with MCDs and refractory epilepsy.

METHODS

Clinical, electrographic, and neuroimaging data were reviewed in eight patients with MCDs who had reflex seizures reproduced during presurgical evaluation.

RESULTS

All eight patients had both reflex and spontaneous seizures. In six, however, drop attacks or axial myoclonic seizures occurred only upon specific sensory stimulation. Reflex seizures were induced by more than one type of stimulus in most patients, but anatomofunctional correlations could usually be invoked. Six patients had significant intellectual impairment. Surgical resection controlled seizures in two patients.

CONCLUSIONS

Reflex seizures in patients with MCDs may be medically refractory and may often manifest as drop attacks or axial myoclonus. Surgical resection of focal lesions can bring reflex seizures under control. Putative mechanisms related to the relatively low frequency of reflex seizures in MCDs are discussed.

Distribution, characterization and clinical significance of microglia in glioneuronal tumours from patients with chronic intractable epilepsy

Cells of the microglia/macrophage lineage represent an important component of different brain tumours. However, there is little information about the microglia/macrophage cell system in glioneuronal tumours and its possible contribution to the high epileptogenecity of these lesions. In the present study, the distribution of cells of the microglia/macrophage lineage was studied by immunocytochemistry for CD68 and human leucocyte antigen (HLA)-DR in a group of glioneuronal tumours, including gangliogliomas (GG, n = 30), and dysembryoplastic neuroepithelial tumours (DNT, n = 17), from patients with chronic intractable epilepsy. A significant number of microglia/macrophage cells were observed in the large majority of glioneuronal tumours, both within the tumour and in the peritumoral region. Activated microglial cells positive for HLA-DR were localized around blood vessels and clustered around tumour neuronal cells. The density of activated microglial cells correlated with the duration of epilepsy, as well as with the frequency of seizures prior to surgical resection. These observations indicate that the presence of cells of the microglial/macrophage cell system is a feature of glioneuronal tumours and is functionally related to epilepsy, either directly in epileptogenesis or through activation following seizure activity.

Localization of breast cancer resistance protein (BCRP) in microvessel endothelium of human control and epileptic brain

PURPOSE

Breast cancer resistance protein (BCRP) is a half adenosine triphosphate (ATP)-binding cassette (ABC) transporter expressed on cellular membranes and included in the group of multidrug resistant (MDR)-related proteins. Recently, upregulation of different MDR proteins has been shown in human epilepsy-associated conditions. This study investigated the expression and cellular distribution of BCRP in human control and epileptic brain, including a large number of both neoplastic and nonneoplastic specimens from patients with chronic pharmacoresistant epilepsy.

METHODS

Several epileptogenic pathologies, such as hippocampal sclerosis (HS), focal cortical dysplasia (FCD), dysembryoplastic neuroepithelial tumor, oligodendroglioma astrocytoma, and glioblastoma multiforme were studied by using Western blot and immunocytochemistry.

RESULTS

With Western blot, we could demonstrate the presence of BCRP in both normal and epileptic human brain tissue. In contrast to P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) 2, BCRP expression levels did not change in tissue from patients with HS, compared with control hippocampus. No BCRP immunoreactivity was observed in glial or neuronal cells, including reactive astrocytes and dysplastic neurons in FCD. BCRP expression was, however, increased in tumor brain tissue. Immunocytochemistry demonstrated that BCRP was exclusively located in blood vessels and was highly expressed at the luminal cell surface and in newly formed tumor capillaries. This localization closely resembles that of P-gp. The higher expression observed in astrocytomas by Western blot analysis was related to the higher vascular density within the tumor tissue.

CONCLUSIONS

These results indicate a constitutive expression of BCRP in human endothelial cells, representing an important barrier against drug access to the brain. In particular, the strong BCRP expression in the microvasculature of epileptogenic brain tumors could critically influence the bioavailability of drugs within the tumor and contribute to pharmacoresistance.

Pediatric Cortical Dysplasia: Correlations between Neuroimaging, Electrophysiology and Location of Cytomegalic Neurons and Balloon Cells and Glutamate/GABA Synaptic Circuits

Seizures in cortical dysplasia (CD) could be from cytomegalic neurons and balloon cells acting as epileptic 'pacemakers', or abnormal neurotransmission. This study examined these hypotheses using in vitro electrophysiological techniques to determine intrinsic membrane properties and spontaneous glutamatergic and GABAergic synaptic activity for normal-pyramidal neurons, cytomegalic neurons and balloon cells from 67 neocortical sites originating from 43 CD patients (ages 0.2-14 years). Magnetic resonance imaging (MRI), (18)fluoro-2-deoxyglucose positron emission tomography (FDG-PET) and electrocorticography graded cortical sample sites from least to worst CD abnormality. Results found that cytomegalic neurons and balloon cells were observed more frequently in areas of severe CD compared with mild or normal CD regions as assessed by FDG-PET/MRI. Cytomegalic neurons (but not balloon cells) correlated with the worst electrocorticography scores. Electrophysiological recordings demonstrated that cytomegalic and normal-pyramidal neurons displayed similar firing properties without intrinsic bursting. By contrast, balloon cells were electrically silent. Normal-pyramidal and cytomegalic neurons displayed decreased spontaneous glutamatergic synaptic activity in areas of severe FDG-PET/MRI abnormalities compared with normal regions, while GABAergic activity was unaltered. In CD, these findings indicate that cytomegalic neurons (but not balloon cells) might contribute to epileptogenesis, but are not likely to be 'pacemaker' cells capable of spontaneous paroxysmal depolarizations. Furthermore, there was more GABA relative to glutamate synaptic neurotransmission in areas of severe CD. Thus, in CD tissue alternate mechanisms of epileptogenesis should be considered, and we suggest that GABAergic synaptic circuits interacting with cytomegalic and normal-pyramidal neurons with immature receptor properties might contribute to seizure generation.

Neurophysiologic findings of neuronal migration disorders: intrinsic epileptogenicity of focal cortical dysplasia on electroencephalography, electrocorticography, and magnetoencephalography

We define specific neurophysiologic characteristics for focal cortical dysplasia, a neuronal migration disorder. We reviewed data from published reports and our patients with focal cortical dysplasia. Our patients underwent preoperative scalp video-electroencephalography (EEG), magnetic resonance imaging (MRI), magnetoencephalography, and intraoperative or extraoperative electrocorticography monitoring. Scalp EEG showed trains of rhythmic epileptiform spike or sharp waves. Positive spikes correlated with early seizure onset, MRI lesion around the rolandic fissure, hemiparesis, and a less favorable outcome. Interictal electrocorticography showed continuous epileptogenic discharges: repetitive electrographic seizures and bursting discharges or continuous or quasicontinuous rhythmic spiking. Ictal electrocorticography showed paroxysmal fast and/or repetitive spiking. Magnetoencephalography showed clustered spike sources within and extending from the lesion. Cortical stimulation gave more frequent, lower-threshold afterdischarges and higher-threshold primary motor function. Focal cortical dysplasias are highly and intrinsically epileptogenic. For surgical seizure control, EEG, electrocorticography, and magnetoencephalography must delineate the intrinsic epileptogenic zone within and extending from the focal cortical dysplasia identified by MRI.

Recurrent intractable seizures in children with cortical dysplasia adjacent to dysembryoplastic neuroepithelial tumor

The purpose of this study was to identify the pathologic features that predict postoperative outcome in children with cortical dysplasia adjacent to dysembryoplastic neuroepithelial tumors. We reviewed the records of children with dysembryoplastic neuroepithelial tumor who underwent epilepsy surgery and who had at least 1 year of surgical follow-up. We divided the dysembryoplastic neuroepithelial tumors into three pathology classes (simple, complex, and nonspecific), categorized adjunctive cortical dysplasia into four types, and compared histopathology with seizure outcomes. We identified 26 children with dysembryoplastic neuroepithelial tumors. Dysembryoplastic neuroepithelial tumors were complex in 19 patients (73%), simple in 6 (23%), and nonspecific in 1 (4%). Cortical dysplasia was adjacent to dysembryoplastic neuroepithelial tumors in 18 patients. Six patients had type IA cortical dysplasia, 5 had type IB, 3 had type IIA, and 1 had type IIB. The 3 remaining patients had repeated surgeries; of these, 2 patients had cortical dysplasias of type IA/IB and 1 was type IIA/IIB. Eight (39%) of 18 patients with dysembryoplastic neuroepithelial tumors and cortical dysplasia required further surgery for recurrent intractable seizures (P < .05), whereas none of 8 patients without cortical dysplasia required additional surgery. Of 13 patients with type I cortical dysplasia, only 4 had a poor seizure outcome, whereas all 5 patients with type II had a poor seizure outcome postoperatively (P < .05). Children with dysembryoplastic neuroepithelial tumor and cortical dysplasia often had recurrent intractable seizures postoperatively and required further epilepsy surgery. Cortical dysplasia adjacent to dysembryoplastic neuroepithelial tumor can play a role in the epileptogenicity of dysembryoplastic neuroepithelial tumor. Complete resection of a dysembryoplastic neuroepithelial tumor and its adjacent cortical dysplasia should be considered.

Subdural EEG Patterns in Children With Taylor-Type Cortical Dysplasia: Comparison With Nondysplastic Lesions

The authors compared interictal and ictal abnormalities from chronic intracranial recordings in children with Taylor-type cortical dysplasia (TTCD) and nondysplastic lesions. Interictal epileptiform discharges and ictal patterns were retrospectively analyzed in 13 children with TTCD and 12 children with nondysplastic lesions (tumor, 4; gliosis, 8). Features analyzed and compared between groups included the morphologic and temporal characteristics and field distribution of ictal and interictal patterns and rapidity of ictal propagation. The frequency of runs of interictal continuous epileptiform discharges (CEDs) or bursts of fast activity did not differ significantly between dysplastic and nondysplastic tissue. Fast frequencies characterized the majority of seizure onsets (49/67) in dysplastic patients and repetitive spikes were more frequent at seizure onset (31/56) in nondysplastic patients (P < 0.002). Field of ictal onset was limited to adjacent cortex and independent of histology. The interval between seizure onset and spread to adjacent or nonadjacent cortex was significantly shorter in dysplastic than nondysplastic patients. Interictal EEG patterns are not specific markers of dysplastic cortex but the morphology of ictal onset differs significantly with dysplastic cortex showing significantly more rapid propagation than nondysplastic cortex. These findings suggest that markers other than CEDs physiologically characterize dysplastic cortex and that children with TTCD exhibit more widespread excitability of neural pathways.

Expression and cellular distribution of high- and low-affinity neurotrophin receptors in malformations of cortical development

An increasing number of observations suggests an important and complex role for both high- (tyrosine kinase receptor, trk) and low- (p75) affinity neurotrophin receptors (NTRs) during development in human brain. In the present study, the cell-specific distribution of NTRs was studied in different developmental lesions, including focal cortical dysplasia (FCD, n = 15), ganglioglioma (GG, n = 15) and dysembryoplastic neuroepithelial tumors, (DNT, n = 10), from patients with medically intractable epilepsy. Lesional, perilesional, as well as normal brain regions were examined for the expression of trkA, trkB, trkC and p75(NTR) by immunocytochemistry. In normal postmortem human cortex, immunoreactivity (IR) for trk and p75(NTR) was mainly observed in pyramidal neurons, whereas no notable glial IR was found within the white matter. All three trk receptors were encountered in high levels in the neuronal component of the majority of FCD, GG and DNT specimens. Strong trkA, trkB and trkC IR was found in neurons of different size, including large dysplastic neurons and balloon cells in FCD cases. In contrast, p75(NTR) IR was observed in only a small number of neuronal cells, which also contain trk receptors. Glial cells with astrocytic morphology showed predominantly IR for trkA in FCD and GG specimens, whereas oligodendroglial-like cells in DNT showed predominently IR for trkB. P75(NTR) IR was observed in a population of cells of the microglial/macrophage lineage in both FCD and glioneuronal tumors. Taken together, our findings indicate that the neuronal and the glial components of malformations of cortical development express both high- and low-affinity NTRs. Further research is necessary to investigate how activation of these specific receptors could contribute to the development and the epileptogenicity of these developmental disorders.

Long-term outcome after epilepsy surgery for focal cortical dysplasia

OBJECT

Reports of outcomes for surgical treatment of cortical dysplasia associated with epilepsy are conflicting due to the inclusion of patients with a wide range of malformations of cortical development. The authors report their experience and the long-term outcome for a subgroup of patients with the histopathological diagnosis of focal cortical dysplasia of Taylor.

METHODS

The records of 22 patients with focal cortical dysplasia of Taylor (15 with the balloon-cell type and seven with the nonballoon-cell type) were reviewed. There were 11 female and 11 male patients whose mean age was 26 +/- 17.6 years (mean +/- standard deviation [SD]) at surgery. The details of their epilepsy evaluation and resection were analyzed. Extent of resection was preoperatively planned using information obtained from long-term intracranial monitoring (15 patients) and/or more definitively determined by histopathologically proven clear margins during resection when feasible (12 patients). The mean duration of follow up was 6.3 +/- 5.1 years (mean +/- SD, range 0.5-15.6 years). Risk factors for epilepsy were trauma (seven patients) or meningoencephalitis (one patient); 14 patients (64%) had no obvious risk factors. The mean age at seizure onset was 9.2 years and the mean duration of their epilepsy was 16.1 +/- 9 years. In two patients there were no adverse findings on magnetic resonance (MR) imaging. In 15 patients (68%), the epileptogenic zone identified on long-term intracranial monitoring extended beyond the abnormality observed on MR images. Focal resection (lesion plus margins) was performed in 14 patients (64%), whereas eight (36%) underwent partial/tailored lobectomy. Two patients underwent multiple subpial transections in addition to partial lesionectomy because their lesions involved the sensorimotor cortex. In these two, functional MR imaging confirmed a normal functional anatomy despite the presence of the cortical dysplasia. Eleven (92%) of 12 patients who underwent resection guided by histopathologically proven clear margins and three (43%) of seven patients who underwent histopathologically proven subtotal resection have remained seizure free. Evidence of clear margins was significantly associated with an improved seizure outcome (p = 0.003). Postoperatively, expected deficits included nondisabling visual field defects, which occurred in three patients (14%), and transient sensorimotor deficits, which appeared in five (23%). Two patients had meningitis, which was successfully treated with antibiotics. Overall, 16 patients (73%) are either seizure free (13 patients), have rare nondisabling partial seizures (one patient), or had one seizure after their medication was changed (two patients). Thirteen patients (59%) have discontinued anticonvulsant medications or are being maintained on monotherapy. Of five patients (23%), two have had rare disabling seizures or significant reduction in their seizure frequency (three patients). One patient's seizures have remained the same.

CONCLUSIONS

Focal cortical dysplasias are a distinct subgroup of malformations of cortical development and have a favorable outcome after resection. The epileptogenic zone often extends beyond the abnormality found on neuroimaging. Resection of the epileptogenic zone guided by histopathologically proven clear margins is associated with an improved seizure outcome.

Malformations of cortical development: burdens and insights from important causes of human epilepsy

Malformations of cortical development (MCD) are important causes of chronic epilepsy in human beings. A blanket term, MCD encompasses many varied developmental disorders with diverse clinical manifestations in patients that neurologists, paediatricians, and learning disability psychiatrists will encounter. Advances in imaging and genetics have led to a significant increase in our understanding of MCD, which has in turn enriched our knowledge of human epileptogenesis and normal brain development and function. In this review, I discuss some of the most common or enlightening MCD: focal cortical dysplasia, periventricular heterotopia, polymicrogyria, band heterotopia and lissencephaly, dysembryoplastic neuroepithelial tumours, and microdysgenesis. Clinical and imaging features, genetic aetiologies, treatments, and the insights that have resulted from MCD study are covered. The burden of epilepsy due to MCD is significant and there is still much to learn about MCD.

Expression and cellular distribution of multidrug transporter proteins in two major causes of medically intractable epilepsy: focal cortical dysplasia and glioneuronal tumors

The cell-specific distribution of multidrug resistance extrusion pumps was studied in developmental glioneuronal lesions, including focal cortical dysplasia (15 cases) and ganglioglioma (15 cases) from patients with medically intractable epilepsy. Lesional, perilesional, as well as normal brain regions were examined for the expression of the multidrug resistance gene 1 encoded P-glycoprotein (P-gp) and the multidrug resistance-associated protein 1 (MRP1) by immunocytochemistry. In normal brain MRP1 expression was below detection, whereas P-gp staining was present only in blood vessels. MRP1 and P-gp immunoreactivity was observed in dysplastic neurons of 11/15 cases of focal cortical dysplasia, as well as in the neuronal component of 14/15 ganglioglioma. Glial cells with astrocytic morphology within the lesion showed multidrug-resistant protein immunoreactivity (P-gp>MRP1). Moderate to strong MRP1 and P-gp immunoreactivity was observed in a population of large ballooned neuroglial cells. P-gp appeared to be most frequently expressed in glial fibrillary acidic protein-positive balloon cells (glial type), whereas MRP1 was more frequently expressed in microtubule-associated protein 2-positive balloon cells (neuronal type). In both types of lesions strong P-gp immunoreactivity was found in lesional vessels. Perilesional regions did not show increased staining in vessels or in neuronal cells compared with normal cortex. The predominant intralesional cell-specific distribution of multidrug transporter proteins supports the hypothesis of a constitutive overexpression as common mechanism underlying the intrinsic pharmaco-resistance to antiepileptic drugs of both malformative and neoplastic glioneuronal developmental lesions.

Expression and cell distribution of group I and group II metabotropic glutamate receptor subtypes in taylor-type focal cortical dysplasia

PURPOSE

Focal cortical dysplasia (FCD) is known to be a major cause of intractable epilepsy. The cellular mechanism(s) underlying the epileptogenicity of FCD remain largely unknown. Because recent studies indicate that metabotropic glutamate receptor subtypes (mGluRs) play a role in epileptogenesis, we investigated the expression and cellular distribution pattern of mGluRs in FCD specimens.

METHODS

Immunocytochemical expression of group I and group II mGluR subtypes was investigated in 15 specimens of human FCD obtained during epilepsy surgery.

RESULTS

Strong mGluR1alpha and mGluR5 (group I mGluRs) immunoreactivity (IR) was observed in the majority of FCD specimens in dysplastic as well as in heterotopic neurons. mGluR1alpha was expressed in a subpopulation of neurons (mainly large dysplastic cells), whereas mGluR5 was represented in a higher percentage of dysplastic neuronal cells. Group II mGluRs (mGluR2/3) IR was observed less frequently than that in group I mGluRs and generally appeared in <10% of the dysplastic neurons. IR for all three mGluR subtypes was observed in balloon cells. mGluR2/3 appeared to be most frequently expressed in glial fibrillary acidic protein (GFAP)-positive balloon cells (glial type), and mGluR1alpha, in microtubule-associated protein (MAP)2-positive cells (neuronal type). mGluR5 was present in the majority of balloon cells. Occasionally glial mGluR1alpha IR was observed in bizarre glial cells with di- or multinuclei. Reactive astrocytes were intensively stained, mainly with mGluR5 and mGluR2/3.

CONCLUSIONS

The cellular distribution of mGluR subtypes, with high expression of mGluR1alpha and mGluR5 in dysplastic neurons, suggests a possible contribution of group I mGluRs to the intrinsic and high epileptogenicity of dysplastic cortical regions.

Characteristics of prolonged afterdischarges in children with malformations of cortical development

We investigated aberrant cortical excitability in malformations of cortical development From subdural electrodes, we recorded afterdischarges lasting > or = 6 seconds in 12 of 13 patients with malformations of cortical development and 6 of 10 pediatric patients with nonmalformations of cortical development and reviewed amperage thresholds, distribution of afterdischarges, and motor responses. In patients with malformation of cortical development, motor response thresholds were high; afterdischarge and motor response thresholds, which essentially overlapped, inversely correlated with age (P < .01); afterdischarge thresholds declined with age; and 8 patients showed afterdischarges in remote sites. In nonmalformation of cortical development, afterdischarge thresholds did not significantly correlate with age; motor response thresholds tended to decline with age; and 2 patients had remote afterdischarges. Adolescent patients with malformations of cortical development had lower afterdischarge thresholds than adolescents with nonmalformation of cortical development (P < .05). From their high afterdischarge (and motor response) thresholds, we concluded that preadolescent patients with malformation of cortical development have less excitable, immature cortices, whereas adolescent patients with malformation of cortical development with low afterdischarge thresholds have hyperexcitable cortices. Remote afterdischarges over focal dysplastic cortex suggest aberrant cortical excitability and neural circuits.

Epileptogenicity of focal malformations due to abnormal cortical development: direct electrocorticographic-histopathologic correlations

PURPOSE

Malformations due to abnormal cortical development (MCDs) are common pathologic substrates of medically intractable epilepsy. The in situ epileptogenicity of these lesions as well as its relation to histopathologic changes remains unknown. The purpose of this study was to correlate the cellular patterns of MCDs with the expression of focal cortical epileptogenicity as assessed by direct extraoperative electrocorticographic (ECoG) recordings by using subdural grids.

METHODS

Fifteen patients with drug-resistant focal epilepsy due to pathologically confirmed MCD who underwent subdural electrode placement for extraoperative seizure localization and cortical mapping between 1997 and 2000 were included in the study. Areas of interictal spiking and ictal-onset patterns were identified and separated during surgery for further pathologic characterization (cellular and architectural). Three pathologic groups were identified: type I; architectural disorganization with/without giant neurons, type IIA; architectural disorganization with dysmorphic neurons, and type IIB; architectural disorganization, dysmorphic neurons, and balloon cells (BCs). The focal histopathologic subtypes of MCDs in cortical tissue resected were then retrospectively correlated with in situ extraoperative ECoG patterns.

RESULTS

Cortical areas with histopathologic subtype IIA showed significantly higher numbers of slow repetitive spike pattern in comparison with histopathologic type I (p = 0.007) and normal pathology (p = 0.002). The ictal onset came mainly from cortical areas with histopathologic type IIA (nine of 15 patients). None of the seizures originated from neocortical areas that showed BC-containing MCD (type IIB).

CONCLUSIONS

This study shows that areas containing BCs are less epileptogenic than are closely located dysplastic regions. These results suggest a possible protective effect of BCs or a severe disruption in the neuronal networks in BCs containing dysplastic lesions. Further studies are needed to elucidate the nature and the potential role(s) of balloon cells in MCD-induced epileptogenicity.

Histopathology of brain tissue from patients with infantile spasms

This chapter reviews the patterns of neuropathologic abnormality encountered in cortical resections performed for the treatment of infantile spasms (ISS) in the broader context of the larger "universe" of neuropathology seen in the central nervous system of infants with this syndrome as well as older children with intractable epilepsy. Although destructive lesions (encephalomalacia), Sturge-Weber-Dimitri syndrome, and even neoplasms can cause ISS, its most common neuropathologic substrate is cortical dysplasia (CD), representing the result of aberrant neuronal migration to the neocortex from the germinal matrix. Ways to recognize CD morphologically and assess its severity are reviewed, as are special stains and immunohistochemical methods that may be useful in confirming the diagnosis. The similarity and relationship between (sporadic) CD and tubers of tuberous sclerosis are discussed. Future potentially fruitful research directions aimed at refining the clinicopathologic analysis of the role of CD in ISS and epilepsies of older children are briefly considered.

Immunohistochemical study of six cases of Taylor's type focal cortical dysplasia: correlation with electroclinical data

PURPOSE

Cortical specimens from six patients operated on for drug-resistant epilepsy diagnosed as Taylor's type focal cortical dysplasia were submitted to neuropathological and immunohistochemical studies.

METHODS

All patients were submitted to presurgical investigations including clinical and neuropsychological evaluations, EEG/video telemetry of ictal and interictal events, magnetic resonance imaging, and ictal and interictal single-photon emission computed tomography (SPECT). Recordings from electrocorticography (ECoG) were obtained in four cases and from subdural electrode implantation in two. Postsurgical follow-up was assessed according to Engel's score. Immunohistochemistry (IHC) was processed for parvalbumin (PV), calbindin D28-K (CB), nonphosphorylated neurofilaments (SMI-311), glial fibrillary acidic protein (GFAP) in all cases.

RESULTS

We found continuous/quasi-continuous spikes and sharp-wave patterns in three cases and frequent repetitive bursting of polyspikes and ECoG seizures in two cases. Every patient showed cortical dyslamination, abnormal and giant neurons, and balloon cells. GFAP immunoreactivity was found in astrocytes and some balloon cells that were less intensely stained. Nonphosphorylated neurofilaments SMI-311 immunoreactivity was found in normal and giant neurons and in some balloon cells, making visible thin neuropils. PV immunoreactivity was present in normal interneurons and in fibers in layers IV-V. PV-negative balloon cells were surrounded by abundant PV-positive fibers. CB immunoreactivity was found mostly in interneurons in layers II-III.

CONCLUSIONS

Our research is inconclusive. More cases should be investigated, and we must draw more accurate anatomic correlations between the ECoG recordings and surgical specimens studied with IHC.