Disrupting the epileptogenic network with stereoelectroencephalography-guided radiofrequency thermocoagulation.

Stereoelectroencephalography-guided radiofrequency thermocoagulation (SEEG-guided RF-TC) is a treatment option for focal drug-resistant epilepsy. In previous studies, this technique has shown seizure reduction by ≥50% in 50% of patients at 1 year. However, the relationship between the location of the ablation within the epileptogenic network and clinical outcomes remains poorly understood. Seizure outcomes were analyzed for patients who underwent SEEG-guided RF-TC and across subgroups depending on the location of the ablation within the epileptogenic network, defined as SEEG sites involved in seizure generation and spread. Eighteen patients who had SEEG-guided RF-TC were included. SEEG-guided seizure-onset zone ablation (SEEG-guided SOZA) was performed in 12 patients, and SEEG-guided partial seizure-onset zone ablation (SEEG-guided P-SOZA) in 6 patients. The early spread was ablated in three SEEG-guided SOZA patients. Five patients had ablation of a lesion. The seizure freedom rate in the cohort ranged between 22% and 50%, and the responder rate between 67% and 85%. SEEG-guided SOZA demonstrated superior results for both outcomes compared to SEEG-guided P-SOZA at 6 months (seizure freedom p = .294, responder rate p = .014). Adding the early spread ablation to SEEG-guided SOZA did not increase seizure freedom rates but exhibited comparable effectiveness regarding responder rates, indicating a potential network disruption.

Lack of spontaneous typical seizures during intracranial monitoring with stereo-electroencephalography.

OBJECTIVE: In the presurgical evaluation of patients with drug-resistant epilepsy (DRE), occasionally, patients do not experience spontaneous typical seizures (STS) during a stereo-electroencephalography (SEEG) study, which limits its effectiveness. We sought to identify risk factors for patients who did not have STS during SEEG and to analyze the clinical outcomes for this particular set of patients. METHODS: We conducted a retrospective analysis of all patients with DRE who underwent depth electrode implantation and SEEG recordings between January 2013 and December 2018. RESULTS: SEEG was performed in 155 cases during this period. 11 (7.2%) did not experience any clinical seizures (non-STS group), while 143 experienced at least one patient-typical seizure during admission (STS group). No significant differences were found between STS and non-STS groups in terms of patient demographics, lesional/non-lesional epilepsy ratio, pre-SEEG seizure frequency, number of ASMs used, electrographic seizures or postoperative seizure outcome in those who underwent resective surgery. Statistically significant differences were found in the average number of electrodes implanted (7.0 in the non-STS group vs. 10.2 in STS), days in Epilepsy Monitoring Unit (21.8 vs. 12.8 days) and the number of cases that underwent resective surgery following SEEG (27.3% vs. 60.8%), respectively. The three non-STS patients (30%) who underwent surgery, all had their typical seizures triggered during ECS studies. Three cases were found to have psychogenic non-epileptic seizures. None of the patients in the non-STS group were offered neurostimulation devices. Five of the non-STS patients experienced transient seizure improvement following SEEG. SIGNIFICANCE: We were unable to identify any factors that predicted lack of seizures during SEEG recordings. Resective surgery was only offered in cases where ECS studies replicated patient-typical seizures. Larger datasets are required to be able to identify factors that predict which patients will fail to develop seizures during SEEG.

Auditory verbal hallucinations as ictal phenomena in a patient with drug-resistant epilepsy.

PURPOSE: The presence of verbal auditory hallucinations is often associated with psychotic disorders and rarely is considered as an ictal phenomena. The aim of this paper is to describe the anatomical structures involved in the genesis of this ictal symptom during epileptic seizures and direct cortical stimulation using stereo encephalography (SEEG). METHOD: The case is of a 31-year-old right-handed female, bilateral speech representation, schizophrenia and with drug-resistant epilepsy and focal aware sensory seizures characterized by ictal verbal auditory hallucinations. She was implanted with depth electrodes, and she was monitored using SEEG recordings. RESULTS: She had focal aware sensory seizures characterized by verbal auditory hallucinations, with the following features: hearing numerous voices (both male and/or female), talking at the same time (not able to distinguish how many). The voices were inside her head, consisted of negative content, and lasted up to two minutes. Some of her focal aware sensory seizures evolved to focal motor seizures and rarely progressed to bilateral tonic clonic seizures. Her neurological examination, her brain MRI and her interictal SPECT were unremarkable. Her PET scan identified mild hypo metabolism over the right temporal and right frontal lobes. Her neuropsychological evaluation showed language laterality undetermined but her functional MRI showed bilateral language representation. On her video-EEG, three seizures were captured with a right posterior temporal onset. A subsequent SEEG showed thirteen typical seizures originating from the posterior temporal neocortical region. The cortical stimulation of the right posterior temporo-parietal neocortical region and right amygdala triggered her typical phenomena, which was multiple voices, inside her head, speaking in the second person, negative content, unable to identify gender, in English, and no side lateralization. CONCLUSION: Verbal auditory hallucinations should be analyzed carefully because they can be part of the seizure presentation. Our case supports the localization of these hallucinations in the right posterior neocortical temporal regions.

Extraoperative electrical stimulation mapping in epilepsy presurgical evaluation: a proposal and review of the literature.

BACKGROUND: Electrical stimulation mapping (ESM) is an important tool for the localization of the seizure onset zone (SOZ) in patients with medically resistant epilepsy (MRE). ESM is the gold standard for the identification of eloquent cortex in epilepsy surgery candidates. However, there is no standard protocol outlining how to perform ESM, to obtain the most useful information possible. The objective of this study, after reviewing the literature concerning ESM, is to propose a unifying technique to validate reliable data across different centers. METHODS: In this manuscript we summarize this technique from its origin to present, and review protocols used in other centers. We also describe a protocol that has been used in our institution, which utilizes depth electrodes. RESULTS: The most common type of ESM uses a "close-loop" system, bipolar and high frequency stimulation (50 Hz). We propose to use a pulse width of 300 µs, current spanning 1-6 mA in depth electrodes and 1-11 mA in subdural-grids. Stimulation time of 5 s maximum and at least 10 s break in between the stimulations. CONCLUSIONS: ESM is a useful tool for understanding eloquent cortex as well as the epilepsy network, although there is no clear consensus regarding how it should be performed.

Role of resective surgery in patients older than 60 years with therapy-resistant epilepsy.

OBJECTIVE: Epilepsy surgery for older adults is controversial owing to their longer duration of epilepsy and perceived higher surgical risk. However, because of an aging population and documented benefit of epilepsy surgery, surgery is considered more frequently for these patients. The authors' objective was to analyze the role of resective surgery in patients older than 60 years and to assess outcomes and safety. METHODS: The authors conducted a retrospective analysis of 595 patients who underwent resective epilepsy surgery at their center from 1999 to 2018. Thirty-one patients aged 60 years or older were identified. Sixty patients younger than 60 years were randomly selected as controls. Population characteristics, results of presurgical evaluations, outcomes, and complications were analyzed. RESULTS: No significant differences were found between the groups in terms of hemisphere dominance, side of surgery, presence of a lesion, and incidence of temporal lobe epilepsy. Epilepsy duration was greater in the older cohort (p = 0.019), and invasive EEG was more commonly employed in younger patients (p = 0.030). The rates of Engel class I outcome at 6 months, 1 year, and 2 years were 89.7%, 96.2%, and 94.7% for the older group and 75% (p = 0.159), 67.3% (p = 0.004), and 75.8% (p = 0.130) for the younger group, respectively. The proportion of seizure-free patients was greatest among those with temporal lobe epilepsy, particularly in the older group. Neurological complication rates did not differ significantly between groups, however medical and other minor complications occurred more frequently in the older group. CONCLUSIONS: Patients older than 60 years had equal or better outcomes at 1 year after epilepsy surgery than younger patients. A trend toward a greater proportion of patients with lesional temporal lobe epilepsy was found in the older group. These results suggest that good seizure outcomes can be obtained in older patients despite longer duration of epilepsy.

Epilepsy surgery in stroke-related epilepsy.

PURPOSE: To provide a descriptive analysis on the presurgical evaluation and surgical management of a cohort of patients with stroke related epilepsy (SRE). METHODS: We retrospectively examined the clinical characteristics, results of non-invasive and invasive presurgical evaluation, surgical management and outcome of consecutive patients with drug-resistant SRE in our institution from January 1, 2013 to January 1, 2020. RESULTS: Twenty-one of 420 patients (5%) who underwent intracranial EEG (iEEG), resective epilepsy surgery and/or vagus nerve stimulation (VNS) placement, had SRE. Of 13 patients who had iEEG, the ictal onset (IO) was exclusively within the stroke lesion in only one patient. In five patients the IO was extra-lesional and in the remaining seven patients it included the stroke lesion as well as extra-lesional structures. The IO included the mesial temporal region in 11 of the 13 patients (85%). The posterior margin of the stroke lesion was always involved. Five patients underwent surgery without iEEG. In total, 10 patients underwent resective surgery, four VNS placement and two had both corpus callosotomy and VNS placement. Of the patients who had resective surgery, nine were Engel I or II at last follow up. CONCLUSION: We found that seizures in patients with drug resistant SRE were more frequently originated in the mesial temporal region than in the stroke lesion itself. Despite the complex epileptic network underlying drug-resistant SRE, a thorough presurgical assessment and adequate use of surgical options can lead to excellent surgical outcomes.

All that glitters: Contribution of stereo-EEG in patients with lesional epilepsy.

OBJECTIVE: To determine the contribution of stereo-EEG for localization purpose in patients with a visible lesion on MRI. BACKGROUND: Intracranial EEG is often used to localize the epileptogenic focus in patients with non-lesional focal epilepsy. Its role in cases where a lesion is visible on MRI can be even more complex and the relationship between the lesion and the seizure onset has rarely been addressed. METHODS: All consecutive patients between February 2013 and May 2018 who underwent stereo-EEG and had a lesion visible on MRI were included. We assessed the localization of the seizure onset and its relationship with the lesion. Clinical, radiological, and electrographic analyses were performed. RESULTS: Stereo-EEG revealed a seizure onset with either partial or no overlap with the lesion seen on MRI in 42 (56 %) of the 75 lesions included. Mesial temporal sclerosis was the only lesion type associated with an exclusively lesional seizure onset (p = 0.003). CONCLUSION: Epilepsy surgery in MRI-positive cases should rely not only the results of lesions seen on MRI, which might be potentially misleading; SEEG is a gold standard method in these cases to define resective borders.

Can we accurately lateralize the epileptogenic zone in patients who have seizure clusters? A study using stereo-electroencephalography.

OBJECTIVE: To determine if the ictal onset recorded with stereoelectroencephalography (SEEG) during clusters of seizures is reliable to identify the laterality of the epileptogenic zone. BACKGROUND: In the presurgical evaluation of patients with focal drug-resistant epilepsy, the presence of bilateral ictal onset is usually associated with a poor surgical outcome. It has been reported that the laterality of seizures can be influenced during seizure clusters, although this remains controversial. Most studies have addressed this issue using scalp EEG which could erroneously determine the laterality of the ictal onset. METHODS: We examined all consecutive patients who underwent SEEG with bilateral hemispheric coverage at our institution between January 2013 and September 2018. We assessed the presence of seizure clusters (clinical or subclinical), their laterality by SEEG and the surgical outcome of the patients. A descriptive clinical and electrographic analysis was performed. RESULTS: Of 143 patients who underwent SEEG recordings, we identified only six patients who had bilateral ictal onset that went on to resective surgery. In all six patients the discordant seizures occurred during a seizure cluster. Three of these patients were seizure free at last follow up. CONCLUSION: Discordant seizures obtained during a seizure cluster may not necessarily mean that the patient has bilateral epilepsy, and therefore a poor post-surgical outcome. Seizure clusters may not reliably lateralize the epileptogenic zone.

Vagus nerve stimulation in patients with therapy-resistant generalized epilepsy.

BACKGROUND: For patients with generalized epilepsy who do not respond to antiseizure medications, the therapeutic options are limited. Vagus nerve stimulation (VNS) is a treatment mainly approved for therapy-resistant focal epilepsy. There is limited information on the use of VNS on generalized epilepsies, including Lennox-Gastaut Syndrome (LGS) and genetic generalized epilepsy (GGE). METHODS: We identified patients with a diagnosis of generalized epilepsy (including LGS and GGE), who underwent VNS implantation at the London Health Sciences Centre and Western University, London, Ontario, since this treatment became available in Canada in 1997 until July 2018. We assessed response to the treatment, including admissions to hospital and complications. RESULTS: A total of 46 patients were included in this study with a history of therapy-resistant generalized epilepsy. The mean age at implantation was 24 years (interquartile range [IQR] = 17.8-31 years), significantly younger in the LGS group (p = 0.02) and 50% (n = 23) were female. The most common etiologies were GGE in 37% (n = 17) and LGS in 63% (n = 29). Median follow-up since VNS implantation was 63 months (IQR: 31-112.8 months). Of the LGS group 41.7% (n = 12) of patients had an overall seizure reduction of 50% or more, and 64.7% (n = 11) in the GGE group without statistical significance between the groups. The best response in seizure reduction was seen in generalized tonic-clonic seizures, with a significant reduction in the GGE group (p = 0.043). There was a reduction of seizure-related hospital admissions from 91.3% (N = 42) preimplantation, to 43.5% (N = 20) postimplantation (p < 0.05). The frequency of side effects due to the stimulation was almost equal in both groups (62.1% in LGS and 64.7% in GGE). CONCLUSIONS: Vagus nerve stimulation should be considered as a treatment in patients with therapy-resistant generalized epilepsy, especially in cases with GGE.

Intracranial Electroencephalographic Monitoring: From Subdural to Depth Electrodes.

At the London Health Sciences Centre Epilepsy Program, stereotactically implanted depth electrodes have largely replaced subdural electrodes in the presurgical investigation of patients with drug-resistant epilepsy over the past 4 years. The rationale for this paradigm shift was more experience with, and improved surgical techniques for, stereoelectroencephalography, a possible lower-risk profile for depth electrodes, better patient tolerability, shorter operative time, as well as increased recognition of potential surgical targets that are not accessible to subdural electrodes.

Six adult patients with septo-optic dysplasia and drug-resistant epilepsy: Clinical findings and course.

Septo-optic dysplasia (SOD) is a rare disorder associated with optic nerve hypoplasia, pituitary abnormalities and agenesis/dysgenesis of midline brain structures including the septum pellucidum and corpus callosum. Though sometimes associated with drug-resistant epilepsy, this association has not been well studied. We report six SOD patients with associated malformation of cortical development (MCD) and drug-resistant epilepsy who underwent video-EEG telemetry at our centre between 1998 and 2016 for drug-resistant epilepsy. ‬Three then underwent surgery; right temporal neocortical resection, right functional hemispherectomy and placement of a vagus nerve stimulator. Clinical findings and the patients' ultimate courses are discussed.

Outcome of temporal lobe epilepsy surgery evaluated with bitemporal intracranial electrode recordings.

BACKGROUND: Temporal lobe epilepsy (TLE) with unclear lateralization may require intracranial implantation of electrodes (IIE). We retrospectively assessed the association between the use of IIE and long-term outcomes in patients undergoing anterior temporal lobectomy (ATL). PARTICIPANTS AND METHODS: We retrospectively reviewed the records of 1,032 patients undergoing epilepsy surgery at our center from 1977 to 2006. Patients who underwent ATL were included. Seizure outcome was assessed through final follow-up. Those who underwent scalp and IIE (mostly evaluated with temporal subdural strip electrodes) were compared. RESULTS: From 497 patients who underwent ATL, 139 did so after IIE placement in the temporal lobes. Mean age at surgery was 32.3±12.3years and median duration of follow-up 24 months (range: 6-36). Fifty-three percent of those evaluated with IIE were seizure-free at their last available visit (vs. 68% evaluated with only scalp EEG, p=0.002). Patients with lesional TLE generally had a better outcome (65.5% seizure free) than those without lesions (56.3%, p=0.093), especially for unilateral TLE diagnosed with IIE. In a multivariate Cox regression analyses adjusted for gender, neuropsychological concordance, pathological findings, and post-operative seizures, bilateral TLE predicted seizure recurrence in IIE patients (HR=2.08, 95% CI: 1.08-4.0, p=0.029). CONCLUSIONS: More than a half of those who undergo IIE in suspected TLE are seizure free after ATL. IIE allows for the identification of surgical candidates.

Coprolalia as a manifestation of epileptic seizures.

OBJECTIVE: The aim of this study was to investigate the lateralizing and localizing value of ictal coprolalia and brain areas involved in its production. METHODS: A retrospective search for patients manifesting ictal coprolalia was conducted in our EMU database. Continuous video-EEG recordings were reviewed, and EEG activity before and during coprolalia was analyzed using independent component analysis (ICA) technique and was compared to the seizures without coprolalia among the same patients. RESULTS: Nine patients were evaluated (five women), eight with intracranial video-EEG recordings (icVEEG). Four had frontal or temporal lesions, and five had normal MRIs. Six patients showed impairment in the language functions and five in the frontal executive tasks. Two hundred six seizures were reviewed (60.7% from icVEEG). Ictal coprolalia occurred in 46.6% of them, always associated with limbic auras or automatisms. They arose from the nondominant hemisphere in five patients, dominant hemisphere in three, and independently from the right and left hippocampus-parahippocampus in one. Electroencephalographic activity always involved orbitofrontal and/or mesial temporal regions of the nondominant hemisphere when coprolalia occurred. Independent component analysis of 31 seizures in seven patients showed a higher number of independent components in the nondominant hippocampus-parahippocampus before and during coprolalia and in the dominant lateral temporal region in those seizures without coprolalia (p=0.009). Five patients underwent surgery, and all five had an ILAE class 1 outcome. SIGNIFICANCE: Ictal coprolalia occurs in both males and females with temporal or orbitofrontal epilepsy and has a limited lateralizing value to the nondominant hemisphere but can be triggered by seizures from either hemisphere. It involves activation of the paralimbic temporal-orbitofrontal network.

Functional MRI of neuronal activation in epilepsy patients with malformations of cortical development.

Malformations of cortical development are disturbances in brain formation that arise from abnormalities affecting the processes of cortical development. Surgical treatment of intractable epilepsy in patients with malformations of cortical development requires localization of both epileptogenic and eloquent cortices. Functional magnetic resonance imaging has been shown to detect the reorganization of activation patterns in such patients. The purpose of this study was to determine whether functional reorganization of the primary sensory and motor cortices occurs in patients with epileptogenic malformations of cortical development. Functional MRI data were obtained for 11 patients (four male, seven female) with a mean age of 36 years (range 18-55 years). The mean age at epilepsy onset was 23 years (range 3-55 years). Twelve healthy controls (six male, six female) with mean age of 33 years (range 28-51 years) were also recruited for comparison. High resolution anatomical MRI was used to confirm the presence and the location of the malformation. All imaging experiments were performed using a 3.0T Siemens Tim Trio whole body MRI. Each subject performed four block-paradigm fMRI experiments to study motor and sensory activation for each hand. A total of 132 image sets were collected for each paradigm over 5.5min (2.5s per image). Each paradigm consisted of seven stimulus periods lasting 30s (12 images) and stimulus onset of 30, 90, 150, 210 and 270s. Functional data were obtained from all eligible patients and compared to those of controls. Reorganization and reduction in function in the motor and sensory areas were observed in patients with cortical dysplasia. Patients with polymicrogyria did not present with significant functional reorganization and patients with heterotopias and coexisting polymicrogyria and/or cortical dysplasia had variable patterns of activation. In summary, this study showed evidence of functional reorganization of sensory and motor cortices in patients with cortical dysplasia development. Such information should be carefully considered in surgical planning and treatment.

Seizures in children with dysembryoplastic neuroepithelial tumors of the brain--A review of surgical outcomes across several studies.

PURPOSE: In children and adolescents, dysembryoplastic neuroepithelial tumors (DNETs) of the brain present with seizures almost 100% of the time, potentially creating significant long-term morbidity and disability despite the generally indolent course of the lesion. These tumors also tend to be quite resistant to anti-epileptic drugs which, themselves, can be associated with long-term side effects and resultant disability. Many clinicians advocate early surgical resection of these lesions, but how effective this approach is, and how aggressive tumor removal should be, continues to be debated. METHODS: We performed a systematic review of the relevant literature to identify all reports of DNET resections in pediatric patients published over the past 20 years. In all, over 3000 MEDLINE abstracts were reviewed, ultimately resulting in 13 studies with 185 pediatric DNET patients to review. RESULTS: Surgical resection of the lesion was effective at improving seizures in over 98% of patients and at achieving long-term seizure freedom in 86%. Surgical resection of DNETs also appeared to be quite safe, with no reported perioperative deaths and an overall rate of postoperative complications of 12%; the vast majority of these complications were transient. CONCLUSIONS: Total gross resection of the lesion was the only factor statistically correlated with long-term seizure freedom (r = 0.63, p = 0.03). However, data remain lacking regarding whether this translates into more extensive procedures-like brain mapping and partial lobectomies-being any more effective than simple lesionectomies alone. Further research is clearly needed to address this and other crucial questions.

Early treatment of a progressive Rasmussen's like syndrome with ganciclovir.

BACKGROUND: Escalating focal sensorimotor seizures, progressive neurologic deficit and cognitive decline with associated typical magnetic resonance imaging (MRI) findings or pathological confirmation constitute the syndrome of Rasmussen's encephalitis. METHODS: Three patients with this clinical scenario had long-term follow-up after being given the antiviral drug ganciclovir 10 mg/kg/day IV for ten days within one to three months of disease onset. RESULTS: Seizures occurred at least hourly and were localized to the Rolandic region. The MRIs were normal in one patient and in two showed changes consistent with ongoing seizures. Two patients, one whose short-term outcome was reported previously, had immediate and sustained cessation of seizures and resolution of their neurologic deficit. One patient with seizures from both hemispheres did not respond and went on to hemispherectomy that confirmed chronic encephalitis. Seizures continued in five other patients treated 6 to 72 months after disease onset. CONCLUSION: The sustained seizure control after ganciclovir in two of three patients suggests this drug may be effective when given early in the course of this subacute intractable focal epilepsy syndrome.

Prevalence of benign epileptiform variants.

OBJECTIVE: There are numerous distinctive benign electroencephalographic (EEG) patterns which are morphologically epileptiform but are non-epileptic. The aim of this study was to determine the prevalence of different benign epileptiform variants (BEVs) among subjects who underwent routine EEG recordings in a large EEG laboratory over 35 years. METHODS: We retrospectively studied the prevalence of BEVs among 35,249 individuals who underwent outpatient EEG recordings at London Health Sciences Centre in London, Ontario, Canada between January 1, 1972 and December 31, 2007. The definitions of the Committee on Terminology of the International Federation of Societies for EEG and Clinical Neurophysiology (IFSECN) were used to delineate epileptiform patterns (Chatrian et al. A glossary of terms most commonly used by clinical electroencephlographers. Electroenceph Clin Neurophysiol 1974;37:538-48) and the descriptions of Klass and Westmoreland [Klass DW, Westmoreland BF. Nonepileptogenic epileptiform electroenephalographic activity. Ann Neurol 1985;18:627-35] were used to categorize the BEVs. RESULTS: BEVs were identified in 1183 out of 35,249 subjects (3.4%). The distribution of individual BEVs were as follows: benign sporadic sleep spikes 1.85%, wicket waves 0.03%, 14 and 6 Hz positive spikes 0.52%, 6 Hz spike-and-waves 1.02%, rhythmic temporal theta bursts of drowsiness 0.12%, and subclinical rhythmic electrographic discharge of adults in 0.07%. CONCLUSION: The prevalence of six types of BEVs was relatively low among the Canadian subjects when compared to the reports from other countries. SIGNIFICANCE: BEVs are relatively uncommon incidental EEG findings. Unlike focal epileptic spikes and generalized spike-and-waves, BEVs do not predict the occurrence of epilepsy. Accurate identification of the BEVs can avoid misdiagnosis and unnecessary investigations.

Usefulness of intracranial EEG in the decision process for epilepsy surgery.

BACKGROUND AND PURPOSE: In patients with discordant results, non-localizing EEG, or bitemporal seizure onset, intracranial monitoring is done to confirm the seizure onset. Our aim was to assess the yield of intracranial recordings in patients with different clinical scenarios. METHODS: The records of all patients who underwent prolonged intracranial EEG monitoring (IEM) at the London Health Sciences Centre, University of Western Ontario, Canada, between 1993 and 1999, identified using our EEG patient database in continuous use since December 1972, were reviewed. Patients were analyzed in the following groups according to perceived increasing degrees of uncertainty of epileptic zone localization-group 1: lesion on MRI congruent with focal ictal and interictal scalp EEG, but findings are subtle and of low level of certainty (n=13), group 2: focal MRI, focal ictal and multifocal interictal scalp EEG (n=11), group 3: focal MRI, non-localizing or incongruent scalp EEG (n=73), group 4: normal of multifocal MRI, focal ictal scalp EEG (n=11), group 5: multifocal MRI, non-localizing scalp EEG (n=18), and group 6: normal MRI, multifocal scalp EEG (n=36). RESULTS: One hundred and seventy one patients underwent IEM at the London Health Sciences Centre between 1993 and 1999. All patients had localization-related epilepsy, plus or minus secondary generalization. IEM was helpful overall in 86% of patients, in 69% of group 1, 36% of group 2, 90% of group 3, 81% of group 4, 100 of group 5 and 92% of group 6. CONCLUSIONS: Our study shows that the yield of the IEM was higher in the groups of patients with lack of congruence between the MRI and the scalp EEG. The yield was lower in patients with congruent but subtle or uncertain scalp EEG and MRI findings.

Epilepsy surgery involving the sensory-motor cortex.

Our aim was to assess the outcome with regard to seizures and neurological function in unselected patients undergoing resective surgery involving the perirolandic area, with or without multiple subpial transections (MSTs). All patients who underwent perirolandic cortical resection or MSTs from 1979 to 2003 at the London Health Sciences Centre were identified. Patients were included if they had seizures originating in the perirolandic area, recorded with subdural electrodes, or if they had scalp recorded seizures and a congruent discrete epileptogenic lesion on MRI in the perirolandic area. Most patients had electrocorticography (ECoG) at the time of surgery. Data collected include pre-operative and post-operative neurological deficits, MRI findings, interictal and ictal scalp EEG, interictal and ictal subdural data, ECoG findings, type and extent of surgery, neuropathologic diagnoses, and seizure outcomes. We studied 52 patients (22 females). The average age at the time of surgery was 33 years, and the average post-operative follow-up was 4.2 years. The most frequent aetiologies were neoplastic in 26 patients (50%), vascular in eight (15%), malformations of cortical development in six (12%), Rasmussen's encephalitis in three (6%) and other aetiologies in nine (17%). Surgery involved the pre-central gyrus in 17 patients, pre- and post-central gyrus in 13, the inferior central region in 11, the post-central gyrus in 7, and the pre-central gyrus and mesial frontal area in 2. At last follow-up 16 patients were in Engel class I (31%), 8 (15%) in class II, 14 (27%) in class III and 14 (27%) in class IV. Residual neurological deficits were present in 26 patients (50%), occurred more frequently in patients > or =25 years old (P < 0.05) and were mild in 14 (54%) patients. In univariate analyses, better seizure outcomes (P < 0.05) occurred in patients whose ECoG showed infrequent post-resectional spikes and no spikes distant to the resection margin, and in resections involving the pre-central and inferior rolandic cortex. In unselected patients with intractable perirolandic epilepsy, many of whom have large, complex epileptogenic lesions, various levels of seizure improvement can be achieved in almost 75% through well-planned surgical resections. New, severe post-operative neurological deficits can occur in 23% of these patients and appear to be more frequent in older patients. Whereas scalp EEG provided limited information to guide surgery, findings on interictal ECoG predicted seizure outcome.