Two magneto-encephalographic epileptic foci did not coincide with the electrocorticographic ictal onset zone in a patient with temporal lobe epilepsy.

To evaluate the usefulness and limitations of magneto-encephalography (MEG) for epilepsy surgery, we compared 'interictal' epileptic spike fields on MEG with ictal electrocorticography (ECoG) using invasive chronic subdural electrodes in a patient with intractable medial temporal lobe epilepsy (MTLE) associated with vitamin K deficiency intracerebral hemorrhage. A 19-year-old male with an 8-year history of refractory complex partial seizures, secondarily generalized, and right hemispheric atrophy and porencephaly in the right frontal lobe on MRI, was studied with MEG to define the interictal paroxysmal sources based on the single-dipole model. This was followed by invasive ECoG monitoring to delineate the epileptogenic zone. MEG demonstrated two paroxysmal foci, one each on the right lateral temporal and frontal lobes. Ictal ECoG recordings revealed an ictal onset zone on the right medial temporal lobe, which was different from that defined by MEG. Anterior temporal lobectomy with hippocampectomy was performed and the patient has been seizure free for two years. Our results indicate that interictal MEG does not always define the epileptogenic zone in patients with MTLE.     

Two magneto-encephalographic epileptic foci did not coincide with the electrocorticographic ictal onset zone in a patient with temporal lobe epilepsy

Abstract

To evaluate the usefulness and limitations of magneto-encephalography (MEG) for epilepsy surgery, we compared 'interictal' epileptic spike fields on MEG with ictal electrocorticography (ECoG) using invasive chronic subdural electrodes in a patient with intractable medial temporal lobe epilepsy (MTLE) associated with vitamin K deficiency intracerebral hemorrhage. A 19-year-old male with an 8-year history of refractory complex partial seizures, secondarily generalized, and right hemispheric atrophy and porencephaly in the right frontal lobe on MRI, was studied with MEG to define the interictal paroxysmal sources based on the single-dipole model. This was followed by invasive ECoG monitoring to delineate the epileptogenic zone. MEG demonstrated two paroxysmal foci, one each on the right lateral temporal and frontal lobes. Ictal ECoG recordings revealed an ictal onset zone on the right medial temporal lobe, which was different from that defined by MEG. Anterior temporal lobectomy with hippocampectomy was performed and the patient has been seizure free for two years. Our results indicate that interictal MEG does not always define the epileptogenic zone in patients with MTLE. [Neurol Res 2001; 23: 830-834]     

Surgical treatment for intractable epilepsy: update and future]

For successful surgical treatment of intractable epilepsy, identification of the epileptogenic area and functional cortex, by using the intracranial electrodes such as subdural and depth electrodes, is important. Since 1994, via chronic subdural electrodes recording, we performed anterior temporal lobectomy with hippocampectomy for 18 patients with temporal lobe epilepsy. For 10 patients with extratemporal lobe epilepsy, cortical resection of the epileptogenic cortex was performed. For the epileptogenic cortex overlapping with functional area, we added the multiple subpial transection. Favorable postoperative seizure outcome was obtained in most of the patients. Although non-invasive presurgical evaluation modalities such as MRI, video-EEG monitoring, MEG, and FDG-PET are useful in the diagnosis of epilepsy, it is impossible to localize precisely the exact epileptogenic zone and functional cortex.     

The magnetic field of epileptic spikes agrees with intracranial localizations in complex partial epilepsy

The magnetoencephalogram (MEG) and electroencephalogram (EEG) were measured during interictal epileptic spikes in nine patients with complex partial seizures. The MEG localization estimates were compared with localizations by intraoperative cortical electrodes, subdural electrodes, stereotaxic depth electrodes, anatomic imaging, postoperative pathologic analysis, and postoperative follow-up. In all patients, MEG localization estimates were in the same lobe as the epileptic focus determined by invasive methods and EEG. In two patients, it was possible to quantify precisely the accuracy of MEG localization by mapping a spike focus that was visually indistinguishable on MEG and cortical recordings. In both patients, MEG localization was approximately 12 mm from the center of the cortical spike focus on intracranial recordings. In eight patients, MEG showed tangential dipolar field patterns on the spontaneous record, but EEG did not. In one patient, a cortical epileptic discharge was detected only on MEG for some discharges and only on EEG for other discharges. The MEG did not detect deep spikes with present levels of environmental noise.     

Magnetoencephalographic localization in pediatric epilepsy surgery: comparison with invasive intracranial electroencephalography.

The object of this study was to determine the concordance of the anatomical location of interictal magnetoencephalographic (MEG) spike foci with the location of ictal onset zones identified by invasive ictal intracranial electroencephalographic recordings in children undergoing evaluation for epilepsy surgery. MEG was performed in 11 children with intractable, nonlesional, extratemporal, localization-related epilepsy. Subsequently, chronic invasive intracranial electroencephalographic monitoring was performed by using subdural electrodes to localize the ictal onset zone and eloquent cortex. Based on the invasive monitoring data, all children had excision of, or multiple subpial transections through, ictal onset cortex and surrounding irritative zones. In 10 of 11 patients, the anatomical location of the epileptiform discharges as determined by MEG corresponded to the ictal onset zone established by ictal intracranial recordings. In all children, the anatomical location of the somatosensory hand area, determined by functional mapping through the subdural electrode array, was the same as that delineated by MEG. Nine of 11 patients became either seizure-free or had a greater than 90% reduction in seizures after surgery, with a mean follow-up of 24 months. MEG is a powerful and accurate tool in the presurgical evaluation of children with refractory nonlesional extratemporal epilepsy.     

Successful epilepsy surgery with a resection contralateral to a suspected epileptogenic lesion.

We report on a case of frontal lobe epilepsy in an eight-year-old girl. Seizure semiology and EEG indicated an epileptogenic zone localized in the mesial frontal structures, without clear-cut lateralization. MRI showed a lesion in the right cingulate gyrus, initially regarded as a hamartoma. Ictal SPECT did not have a localization value. MR spectroscopy revealed two metabolic abnormalities: one in the area of the MRI lesion and a second contra-laterally. Invasive monitoring using subdural electrodes covering the convexity and mesial part of the right frontal lobe including mesial strips with bilateral contacts was used. The invasive monitoring failed to localize ictal onset in the right hemisphere; however, electric stimulation induced seizures from electrodes facing the left supplementary sensorimotor area ("through" the falx cerebri). We re-implanted the electrodes over the left frontal lobe and the second invasive monitoring clearly localized the ictal onset zone in the left supplementary sensorimotor area, which was subsequently resected. Histopathology found MRI-negative focal cortical dysplasia. The contralateral lesion was reassessed as nonspecific enlargement of perivascular spaces. The patient has been seizure-free for more than two years.[Published with video sequences].     

Pre- and intra-operative evaluation of epileptic children with intractable seizure disorders: the hospital for sick children

The pediatric epilepsy management team in the Hospital for Sick Children, Toronto, Canada, consists of neurologists, neurophysiologists, neurosurgeons, neuropyschologists, clinical nurse specialist/nurse practitioners, social workers, EEG technologists and psychiatrists. The patients are initially referred to us for the diagnosis of seizure disorders. Epileptic foci and eloquent cortices are identified by neurophysiological studies such as EEG, MEG and SEP. Epileptogenic lesions can be visualized by MRI, the language, motor and sensory cortices by fMRI and the regions of hypoperfusion and hypometabolism in the epileptic foci, by SPECT and PET, respectively. The results of these studies are then discussed by members of the team. For patients with lesional epilepsy, an intraoperative image guided system and intraoperative electrocorticography are used, when lesionectomy, lobectomy and additional multiple subpial transection (MST) are performed. Patients without an identifiable lesion require intracranial invasive video EEG using subdural grids or depth electrodes, which are constructed based on MEG spike sources, seizure semiology and scalp video EEG. After the identification of the epileptogenic and functional zones, maximum cortical excision and MST are performed to control seizures and to minimize functional deficits. Pediatric neurologists should assess the intractability of epilepsy, identify the epileptogenic zone, determine the excisable epileptic region, and minimize postoperative side effects, thereby leading the epilepsy management team.     

EEG and MEG source analysis of single and averaged interictal spikes reveals intrinsic epileptogenicity in focal cortical dysplasia

PURPOSE: Simultaneous interictal EEG and magnetoencephalography (MEG) recordings were used for noninvasive analysis of epileptogenicity in focal cortical dysplasia (FCD). The results of two different approach methods (multiple source analysis of averaged spikes and single dipole peak localization of single spikes) were compared with pre- and postoperative anatomic magnetic resonance imaging (MRI). PATIENTS: We studied nine children and adolescents (age, 3.5-15.9 years) with localization-related epilepsy and FCD diagnosis based on MRI. Five patients underwent epilepsy surgery, two of them after long-term recording with subdural grid electrodes, and one after intraoperative electrocorticography. METHODS: The 122-channel whole-head MEGs and 33-channel EEGs were recorded simultaneously for 25 to 40 min. Interictal spikes were identified visually and used as templates to search for similar spatiotemporal spike patterns throughout the recording. With the BESA program, similar spikes (r > 0.85) were detected, averaged, high-pass filtered (5 Hz) to enhance spike onset, and subjected to multiple spatiotemporal source analysis with a multishell spherical head model. Peak activity from single spikes was modeled by single dipoles for the same subset of spikes. Source localization was visualized by superposition on T1-weighted MRI and compared with the lesion identified in T1- and T2-weighted MRI. In the five cases undergoing epilepsy surgery, the results were correlated with invasive recordings, postoperative MRI, and outcome. RESULTS: In all cases, the analysis of averaged spikes showed a localization of onset- and peak-related sources within the visible lesion for both EEG and MEG. Of the single spikes, 128 (45%; total 284) were localizable at the peak in MEG, and 170 (60%) in EEG. Of these, 91% localized within the lesion with MEG, and 93.5% with EEG. In three of five patients operated on, the resected area included the onset zones of averaged EEG and MEG spike activity. These patients had excellent postoperative outcome, whereas the others did not become seizure free. CONCLUSIONS: Consistent MEG and EEG spike localization in the lesional zone confirmed the hypothesis of intrinsic epileptogenicity in FCD.     

Surgical treatment of medically refractory epilepsy in childhood

Twenty five percent of children with epilepsy continue to seize despite best medical management and may be defined as medically refractory. Many children with medically refractory localization-related epilepsy, i.e. seizures which originate in a particular area of brain and secondarily spread to involve other brain regions, may benefit from a variety of surgical treatments including hemispherectomy, corpus callosotomy, focal cortical resection of the temporal lobe, focal cortical resection of extratemporal regions of brain, and multiple subpial resections. A successful outcome from epilepsy surgery is generally defined as a seizure-free state with no imposition of neurologic deficit. In order to achieve these twin goals two criteria must be fulfilled. First, precise localization of the epileptogenic zone in the brain is necessary. The epileptogenic zone may be defined as the region of epileptogenic cerebral cortex whose removal will result in a seizure-free state. Second, one must determine the anatomic localization of eloquent cortex in brain in order to spare these areas during any planned cortical excision of epileptogenic cortex. Several diagnostic measures may be used to achieve a successful surgical outcome. A clinical history to ascertain the earliest symptom in the clinical progression of the seizure (semiology) is imperative as is ictal and interictal scalp EEG, neuropsychological testing, magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission computerized tomography (SPECT), interictal magnetoencephalography (MEG). In the typical child undergoing evaluation for epilepsy surgery, if the clinical, neuropsychological, EEG, and radiological data are all concordant and point to the same area of epileptogenicity in brain, cortical excision of the suspected epileptogenic zone is undertaken. However, if the data are discordant, and/or the epileptogenic zone resides wholly or in part within eloquent cortex, invasive intracranial monitoring from depth and/or subdural electrodes during a seizure is required to map out the areas of epileptogenicity in brain. The assessment of potential risks and benefits for this type of epilepsy surgery in children involve complex age-related issues, including the possible impact of uncontrolled seizures, medication, or surgery, on learning and development.     

Magnetoencephalography in partial epilepsy: Clinical yield and localization accuracy

The goals of this study were to determine (1) the yield of magnetoencephalography (MEG) according to epilepsy type, (2) if MEG spike sources colocalize with focal epileptogenic pathology, and (3) if MEG can identify the epileptogenic zone when scalp ictal electroencephalogram (EEG) or magnetic resonance imaging (MRI) fail to localize it. Twenty-two patients with mesial temporal (10 patients), neocortical temporal (3 patients), and extratemporal lobe epilepsy (9 patients) were studied. A 37-channel biomagnetometer was used for simultaneously recording MEG with EEG. During the typical 2–3–hour MEG recording session, interictal epileptiform activity was observed in 16 of 22 patients. MEG localization yield was greater in patients with neocortical epilepsy (92%) than in those with mesial temporal lobe epilepsy (50%). In 5 of 6 patients with focal epileptogenic pathology, MEG spike sources were colocalized with the lesions. In 11 of 12 patients with nonlocalizing (ambiguous abnormalities or normal) MRI, MEG spike sources were localized in the region of the epileptogenic zone as ultimately defined by all clinical and EEG information (including intracranial EEG). In conclusion, MEG can reliably localize sources of spike discharges in patients with temporal and extratemporal lobe epilepsy. MEG sometimes provides noninvasive localization data that are not otherwise available with MRI or conventional scalp ictal EEG.