The role of magnetoencephalography in epilepsy surgery

Zulma S. Tovar-Spinoza Divisions of Neurosurgery and

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Ayako Ochi Neurology, The Hospital for Sick Children, University of Toronto, Ontario, Canada

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James T. Rutka Divisions of Neurosurgery and

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Cristina Go Neurology, The Hospital for Sick Children, University of Toronto, Ontario, Canada

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Hiroshi Otsubo Neurology, The Hospital for Sick Children, University of Toronto, Ontario, Canada

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Epilepsy surgery requires the precise localization of the epileptogenic zone and the anatomical localization of eloquent cortex so that these areas can be preserved during cortical resection. Magnetoencephalography (MEG) is a technique that maps interictal magnetic dipole sources onto MR imaging to produce a magnetic source image. Magneto-encephalographic spike sources can be used to localize the epileptogenic zone and be part of the workup of the patient for epilepsy surgery in conjunction with data derived from an analysis of seizure semiology, scalp video electroencephalography, PET, functional MR imaging, and neuropsychological testing. In addition, magnetoencephalographic spike sources can be linked to neuronavigation platforms for use in the neurosurgical field. Finally, paradigms have been developed so that MEG can be used to identify functional areas of the cerebral cortex including the somatosensory, motor, language, and visual evoked fields.

The authors review the basic principles of MEG and the utility of MEG for presurgical planning as well as intra-operative mapping and discuss future applications of MEG technology.

Abbreviations used in this paper:

CSF = cerebrospinal fluid; EEG = electroencephalography; fMR = functional magnetic resonance; MEG = magnetoencephalography; MEGSS = MEG spike source; SAM = synthetic aperture magnetometry; SEF = somatosensory evoked magnetic field; VEEG = video EEG.

Epilepsy surgery requires the precise localization of the epileptogenic zone and the anatomical localization of eloquent cortex so that these areas can be preserved during cortical resection. Magnetoencephalography (MEG) is a technique that maps interictal magnetic dipole sources onto MR imaging to produce a magnetic source image. Magneto-encephalographic spike sources can be used to localize the epileptogenic zone and be part of the workup of the patient for epilepsy surgery in conjunction with data derived from an analysis of seizure semiology, scalp video electroencephalography, PET, functional MR imaging, and neuropsychological testing. In addition, magnetoencephalographic spike sources can be linked to neuronavigation platforms for use in the neurosurgical field. Finally, paradigms have been developed so that MEG can be used to identify functional areas of the cerebral cortex including the somatosensory, motor, language, and visual evoked fields.

The authors review the basic principles of MEG and the utility of MEG for presurgical planning as well as intra-operative mapping and discuss future applications of MEG technology.

Pediatric epilepsy surgery is a constantly evolving field that offers patients with drug-resistant epilepsy a better chance for seizure control without causing additional morbidity. Over the years, advances in the knowledge of neuromagnetism have allowed for the integration of MEG data with MR imaging to produce magnetic source images. Magnetoencephalography has proven to be a valuable presurgical tool in identifying the epileptogenic zone and eloquent brain cortex, and in predicting surgical outcomes in a subset of children with intractable epilepsy.27,28,48,55

An Overview of MEG

Introduced in 1968,9 MEG is a technique that allows for the measurement of extracranial magnetic fields generated by massive synchronized intraneuronal electric currents. Magnetoencephalography uses a “superconducting quantum interference device” (SQUID)34,39 to amplify small magnetic fields generated by intracranial neuronal activity. The flow of electrical current in this activity must be parallel to the surface of the skull so that a perpendicular magnetic field can be generated and detected by MEG sensors. Current MEG systems use multiple detector coils arranged over the convexity of the skull to record magnetic fields over almost the entire brain.20

Comparison of MEG and EEG

The question of whether MEG has advantages over EEG has been widely discussed.4,29,35,56,65 Although both EEG and MEG are based on analysis of synchronized electrical discharges originating from cortical pyramidal cells, MEG has several advantages over conventional scalp EEG. The techniques of EEG and MEG can be compared as follows.10,35,49

Neuronal Currents

Magnetoencephalography primarily detects the magnetic fields induced by intracellular currents, whereas scalp EEG is sensitive to electrical fields generated by extracellular currents.

Orientation of Currents

Although MEG is more sensitive in detecting currents that are tangential to the surface of the scalp, EEG is sensitive to tangential and radial neuronal activities.

Sensitivity

Epileptiform spikes detected by MEG are 1/1,000,000 times smaller than environmentally generated magnetic noise. Hence, to be able to capture the weak magnetic signal, the biomagnetometer must be housed in a shielded room with high-permeability metals to reduce competing ambient magnetic noise.70

Detected Field

Magnetoencephalography requires 3–4 cm2 of synchronized cortical epileptic activity to detect an epileptic spike,38,46 whereas at least 6–20 cm2 of synchronized cortical area is needed for scalp EEG spike detection.11,69

Conductivity

Magnetic fields are theoretically not distorted by the tissue conductivity of the scalp, skull, CSF, and brain; in contrast, electrical fields may be distorted by the skull and CSF.

Accuracy of Source Localization

Magnetoencephalography provides better spatial resolution of source localization (2–3 mm) than EEG (7–10 mm).31,49

Electrodes and Sensor Coils

For EEG, electrodes are placed on the scalp. Magnetoencephalography is performed using a dewar that contains multiple sensor coils, which do not touch the patient's head.

Ictal Recording With Head Movement

Because epileptic seizures may be associated with head movements, MEG may lose the precise localization of epileptic sources. Although the ictal wave form can still be recorded, the sensors are inaccurate and superimposition on MR images may not be worthwhile.65

Signal-To-Noise Ratio

A recent study comparing the signal-to-noise ratios of hypothetical sources in different areas of the brain indicated an advantage for MEG over EEG in the study of neocortical epilepsies, although the estimated signal-to-noise ratios were comparable in the temporal lobe.12

Analysis

Magnetoencephalographic data can be analyzed by source modeling techniques, which allow for localization in 3 dimensions.2,14 Although source modeling techniques are available for scalp EEG, MEG source modeling is generally simpler and more accurate for technical reasons.5

Cost

The MEG technology and appropriate source analysis software is several times more expensive than the most sophisticated EEG device.32

The Utility of MEG for Presurgical Evaluation

Localization of the Epileptogenic Zone

Different strategies are used to determined the epileptogenic zone.24 The Subcommission for Pediatric Epilepsy Surgery of the Commission on Neurosurgery of the International League Against Epilepsy (ILAE) has recently published guidelines for the presurgical evaluation of children with epilepsy based on a survey collecting data from 543 patients in 20 pediatric epilepsy programs in the US, Europe, and Australia.24,57 The guidelines suggest that in addition to initial evaluation by an experienced clinician, EEG (including sleep recording) and MR imaging are mandatory. While VEEG recording is strongly recommended in all children, 80% of the centers used ictal-SPECT, 85% used FDG-PET, 70% used fMR imaging for language localization, 35% used MEG/magnetic source imaging, and 50% performed an intracarotid amobarbital procedure (Wada test). Only 3 centers used all presurgical tests. Neuropsychological and neuropsychiatric evaluations are also recommended.24

At the Hospital for Sick Children in Toronto, children with intractable epilepsy are considered candidates for surgery following analyses of seizure semiology, prolonged scalp VEEG recordings, MR imaging, and the distribution of MEGSSs.43,67 Neuropsychological evaluations are performed in cooperative school-aged children to determine preoperative verbal and memory function. Language dominance is determined by neuropsychological testing, fMR imaging, and MEG. In atypical cases with bilateral or ambiguous language findings, we perform a Wada test.30,64

The relationship between ictal and interictal findings and clinical presentation on scalp VEEG and MEG results should be correlated to initiate the map of the epileptogenic network.43 Concordant lateralization of the scalp VEEG findings and the MEGSSs can point to the primary epileptogenic hemisphere and identify those children who are candidates for surgical treatment. Discordant data from the scalp VEEG results and MEGSSs typically indicate that the epileptogenic zone cannot be lateralized, and in such cases surgical candidacy for local resection becomes less likely.44

The distribution of MEGSSs is defined by their number and density. In our center, we have defined “clusters” as comprising 20 or more spike sources within an area 1-cm in diameter, “small clusters” consist of 6–19 spike sources within 1 cm, and scatters consist of < 6 spike sources, irrespective of the distance between sources (Fig. 1).28 It has been our experience that, defined in this fashion, a single cluster frequently correlates with the seizure onset zone, part of the symptomatogenic zone, and the active irritative zone on intracranial VEEG recording.45

Fig. 1.
Fig. 1.

Coronal, sagittal, and axial MR images showing examples of MEGSS distribution patterns consisting of MEGSS clusters (closed circles), small clusters (open triangles), and scatters (open squares). The MEGSSs were overlaid on single-plane MR images. Reprinted with permission from Iida K, et al: J Neurosurg 102 (2 Suppl):187–196, 2005.

The utility of interictal MEG for localizing the epileptogenic zone has been demonstrated on the basis of postsurgical seizure freedom.48,56,68 Magnetoencephalography has been used both in children with lesional epilepsy48 and children with nonlesional epilepsy.58 In cases of malformations of cortical development, the removal of both the MEG spike cluster and the MR imaging lesion are essential for favorable outcomes. In cases of tumors with extramarginal MEGSSs, lesionectomy alone yields a favorable outcome.48 In nonlesional cases, the seizure outcome after resection of MEGSSs has been reported to be successful when the ictal onset zone was restricted on the intracranial VEEG. Postoperative seizure freedom was less likely to occur in children with bilateral clusters of MEGSSs or only scattered MEGSSs, multiple seizure types, or incomplete resection of the proposed epileptogenic zone.39,58

Functional Mapping

In cases in which the epileptogenic zone is near eloquent regions of the brain, precise delineation of these functional areas is required to avoid neurological deficits.67

Localization of the Primary Sensorimotor Cortex

The primary motor cortex, somatosensory cortex, and central sulcus cannot be reliably identified by visual inspection alone. This may be due to displacement of the Rolandic region structures by tissue compression, brain edema,71 or epilepsy that can cause functional reorganization of neuronal pathways, especially in the developing brains of children.1,19 Direct cortical stimulation and assessment of somatosensory evoked potentials are considered to be the most accurate methods for the localization of the central sulcus.33,37 Localization of the central sulcus by MEG can be obtained by the determination of the SEF. The SEF has been validated as being accurate in approximately 90% of cases through the use of direct cortical stimulation and somatosensory evoked potential phase reversals through electrocorticography in adults.17,18,61 Interestingly, the SEF can be reliably studied in infants and young children with epilepsy even while they are receiving total intravenous anesthesia.6

Language Lateralization

Language lateralization can be determined by means of MEG using various language paradigms such as word recognition tasks,54 silent reading,26 picture naming, and verb generation.7 An 89–95% concordance rate has been found between MEG language mapping and results from Wada testing.53 Magnetoencephalographic language studies in patients with chronic seizure disorders of left hemispheric onset have demonstrated atypical language organization. In these children, right hemispheric language competence on nonverbal functions is frequently found.8,36 It should be noted that normative MEG language data obtained in healthy children are still somewhat scarce,41,59 although the localization of auditory evoked potentials51 and the effect of age on language perception have been studied.52

Visual Evoked Field Determination

Magnetoencephalography has been used for preoperative visual field detection in children and adults with occipital seizures.2 This paradigm is helpful in determining the relationship between the visual cortex and brain lesions. The localization of the visual evoked field on MEG should always prompt consideration of a surgical approach that would retain the visual pathways.21

Applications of MEG in Intracranial VEEG

Creating the Neurosurgical Map

The co-registered MEG data are overlaid onto axial 3D fast spoiled gradient and T1-weighted volume MR images, generating a high-resolution magnetic source image.18 We design subdural electrode grids for individual patients to cover the interictal MEGSSs, areas from which ictal and interictal scalp VEEG data have been obtained, and regions of functional cortex.67 The size of the individual intracranial subdural electrode array is prepared from data derived from 3D MR imaging, MEG SEF, and MEGSSs.27

Neuronavigation

Magnetoencephalographic data are incorporated into the neuronavigation system to obtain a 3D localization of the MEGSSs and somatosensory, auditory, and visual evoked magnetic fields. This information is then co-registered to the cerebral cortex at the time of surgery.50 The neuronavigation system guides neurosurgeons in the placement of the subdural grid to cover the locations of the SEF and margins of the MEGSSs, which are marked with letters during the procedure. Intraoperative digital photographs are then taken of the surgical field for future use in the development of the surgical plan once enough seizures have been captured.62

Determining the Extent of Resection

After the intracranial electrodes are implanted for extra-operative recording of seizures, the patient routinely undergoes a brain CT scan within 24 hours. Data from the postoperative CT in terms of grid localization are fused with the preoperative magnetoencephalographic data to map the subdural grid to the region of interest on the cerebral cortex.

The ictal onset zone, the symptomatogenic zone, and the irritative zone are identified by the intracranial VEEG recording and mapped to the appropriate regions under the subdural grid.60 After several habitual seizures are captured, the area to be resected is mapped by taking into consideration the ictal onset zone, the irritative zone, and MEGSSs. The final neurosurgical map is produced taking into account the potential for seizure control, possible functional deficits, and the patient's quality of life.43

The Role of MEG After Failed Epilepsy Surgery

Persistent seizures occur in 20–60% of patients following resection procedures for intractable epilepsy.15,41,42,63 The majority of patients have recurrent or persistent seizures emanating from the same location of the brain because of insufficient initial resection, activation of mesiotemporal structures in temporal lobe epilepsy,22,72,73 or the development of an independent zone of epileptogenesis nearby.3,13 Brain shifts following resection may cause gross distortions of topographic anatomy in these patients.3 In this situation, MEG is superior to scalp EEG, because the magnetic field is not distorted by skull defects and CSF collections, which may cause false localization on scalp EEG.55 Magnetoencephalography has been used to successfully localize the residual epileptogenic zone in patients with late-onset recurrent seizures in whom MR imaging reveals no residual abnormality and ictal scalp EEG is not lateralizing.41

The Utility of MEG in Epilepsy Surgery: Illustrative Case

A 4-year-old previously healthy boy had episodes of auditory and visual hallucinations that occurred during sleep as he aroused. The parents noted eye deviation to the right side followed by eye twitching with sparing of consciousness during wakefulness and sleep. These events increased in frequency up to multiple events per hour.

A CT scan of the brain demonstrated no abnormality. Scalp VEEG showed electroclinical seizures arising from the right occipital region and propagating to the right parietal region. An MR imaging study of the brain showed abnormal signal with cortical thickening over the right calcarine cortex and parietal lobe suggestive of focal cortical dysplasia (Fig. 2). Magnetoencephalography showed a cluster of dipole sources in the right mesial parietooccipital region (Fig. 3).

Fig. 2.
Fig. 2.

Axial FLAIR MR images showing abnormal signal in the subcortical white matter in the right mesial occipital region (white arrows).

Fig. 3.
Fig. 3.

Axial T1-weighted MR images showing 4 (left) and 2 (right) of 37 MEG spike sources over the right pari-etooccipital region around the MR imaging abnormality. (Closed triangles represent the location of MEGSSs and tails indicate the orientation of the MEG spike sources). The white arrow indicates extension of focal cortical dysplasia in the right parietal lobe just above the parietooccipital fissure.

Eleven months later, the boy's seizures became refractory to treatment with multiple antiepileptic drugs. He underwent placement of a right temporoparietooccipital grid and 2 depth electrodes to the superior and inferior margins of the clustered MEGSSs and 1 interhemispheric strip electrode covering the calcarine cortex (Fig. 4). The patient experienced 4 electroclinical seizures consisting of eye twitching during 4-day intracranial VEEG monitoring period. The ictal onset zone was localized to the right mesial occipital region and right parietooccipital junction close to the midline, spreading to the lateral parietal and occipital regions. He underwent a right occipital lobectomy and a corticectomy over the right parietal region posterior to the sensory cortex. A postoperative right homonymous hemianopsia was expected and found. The final neuropathological diagnosis was focal cortical dysplasia with balloon cells. As of this writing (6 months after surgery), the child continues to be treated with antiepileptic medication and remains seizure free.

Fig. 4.
Fig. 4.

Left: Intraoperative photograph showing a subdural grid containing 100 electrodes on the right temporoparietooccipital region, 2 depth electrodes to the superior (D31–34) and inferior (D41–44) margins of the clustered MEG spike sources, and 1 strip electrode (S1–4) in the interhemispheric fissure covering the calcarine cortex. Extraoperative electrical stimulation on only 1 electrode (Electrode 11, yellow open circle) demonstrated the hand motor cortex. Somatosensory evoked potential testing using the grid electrodes showed that Electrodes 10–12 and 21 (yellow open squares) represent motor cortex and Electrodes 22 and 34 (green open squares) represent sensory cortex. The ictal onset zone (red squares) was confirmed in the right mesial occipital region (D33, 34) and right parietooccipital junction close to the midline (S1–4). Seizures spread to the lateral parietal and occipital region. The patient underwent a right occipital lobectomy and cortical excision over the right parietooccipital region including the cluster of MEG spike sources and MR imaging lesion (yellow line). Right: A 3D MR image reconstructed from thin-sliced T1-weighted MR images showing a total of 37 MEG spike sources (purple dots). Twenty-six MEG spike sources were clustered in the right occipital region (white arrow). The other 11 scattered MEG spike sources were located in the right temporoparietooccipital region.

Future Applications of MEG Technology

Several methods are being developed to advance the analysis of the 3D magnetic-field data collected by multiple sensor coils for improvement of the localization of epileptic foci and eloquent cerebral functions. In the future, when interictal epileptiform discharges on scalp EEG show a diffuse hemispheric distribution or bilateral synchronous spike waves, dynamic statistical parametric maps and gradient magnetic-field topography23,25,66 may be used to demonstrate dynamic changes of epileptic spikes moving within the epileptic zone. Today, spatial filtering can be applied to MEG data by means of SAM. The SAM virtual sensor analysis reveals morphological characteristics, location, and distribution of epileptiform discharges similar to those shown by subdural EEG recordings.47 Noninvasive localization of the primary motor cortex16 and language function40 can be reliably carried out using SAM, providing a robust and accurate measurement of cortical functions for the purpose of surgical guidance.

Ideally, what would be extremely useful would be the development of MEG technology to map ictal data onto the neurosurgical map. As MEG technology improves and as software design advances to take into account such factors as head movement during seizure onset, the precise identification of the ictal onset zone by MEG may become a reality.

Disclosure

Dr. Tovar-Spinoza was supported by a fellowship from the Wiley Fund at the Hospital for Sick Children. This work was also supported by a grant from the Wiley Fund at the Hospital for Sick Children. The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Acknowledgments

We thank the members of the epilepsy surgery team at the Hospital for Sick Children who made this work possible.

References

  • 1

    Akai T, , Otsubo H, , Pang EW, , Rutka JT, , Chitoku S, & Weiss SK, et al.: Complex central cortex in pediatric patients with malformations of cortical development. J Child Neurol 17:347352, 2002

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Alberstone CD, , Skirboll SL, , Benzel EC, , Sanders JA, , Hart BL, & Baldwin NG, et al.: Magnetic source imaging and brain surgery: presurgical and intraoperative planning in 26 patients. J Neurosurg 92:7990, 2000

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3

    Awad IA, , Nayel MH, & Luders H: Second operation after the failure of previous resection for epilepsy. Neurosurgery 28:510518, 1991

  • 4

    Barkley G, & Baumgartner C: MEG and EEG in epilepsy. J Clin Neurophysiol 20:163178, 2003

  • 5

    Baumgartner C, & Pataraia E: Revisiting the role of magnetoencephalography in epilepsy. Curr Opin Neurol 19:181186, 2006

  • 6

    Bercovici E, , Pang EW, , Sharma R, , Mohamed IS, , Imai K, & Fujimoto A, et al.: Somatosensory-evoked fields on magnetoencephalography for epilepsy infants younger than 4 years with total intravenous anesthesia. Clin Neurophysiol 119:13281334, 2008

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7

    Bowyer SM, , Moran JE, , Weiland BJ, , Mason KM, , Greenwald ML, & Smith BJ, et al.: Language laterality determined by MEG mapping with MR-FOCUSS. Epilepsy Behav 6:235241, 2005

  • 8

    Breier JI, , Castillo EM, , Simos PG, , Billingsley-Marshall RL, , Pataraia E, & Sarkari S, et al.: Atypical language representation in patients with chronic seizure disorder and achievement deficits with magnetoencephalography. Epilepsia 46:540548, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9

    Cohen D: Magnetoencephalography: evidence of magnetic fields produced by alpha-rhythm currents. Science 161:784786, 1968

  • 10

    Cohen D, & Cuffin BN: Demonstration of useful differences between the magnetoencephalogram and electroencephalogram. Electroencephalogr Clin Neurophysiol 56:3851, 1983

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 11

    Cooper R, , Winter AL, , Crow HJ, & Walter WG: Comparison of subcortical, cortical and scalp activity using chronically indwelling electrodes in man. Electroencephalogr Clin Neurophysiol 18:217228, 1965

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    de Jongh A, , de Munck JC, , Goncalvez SI, & Ossenblok P: Differences in MEG/EEG epileptic spike yields explained by regional differences in signal-to-noise ratios. J Clin Neurophysiol 22:153158, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13

    Drake J, , Hoffman HJ, , Kobayashi J, , Hwang P, & Becker LE: Surgical management of children with temporal lobe epilepsy and mass lesions. Neurosurgery 21:792797, 1987

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Ebersole JS, , Squires KC, , Eliashiv SD, & Smith JR: Applications of magnetic source imaging in evaluation of candidates for epilepsy surgery. Neuroimaging Clin N Am 5:267288, 1995

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 15

    Engel J, , Van Ness P, & Rasmussen T, et al.: Outcome with respect to epileptic seizures. Engel J: Surgical Treatment of the Epilepsies ed 2 New York, Raven Press, 1993. 609621

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Gaetz W, , Cheyne D, , Rutka J, , Drake J, , Benifla M, & Strantzas S, et al.: Pre-surgical localization of primary cortex in paediatric patients with brain lesions using spatially filtered MEG. Neurosurgery In press 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Gallen CC, , Schwartz BJ, , Bucholz RD, , Malik G, , Barkley GL, & Smith J, et al.: Presurgical localization of functional cortex using magnetic source imaging. J Neurosurg 82:988994, 1995

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18

    Gallen CC, , Sobel DF, , Waltz T, , Aung M, , Copeland B, & Schwartz BJ, et al.: Noninvasive presurgical neuromagnetic mapping of somatosensory cortex. Neurosurgery 33:260268, 1993

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19

    Gregorie EM, & Goldring S: Localization of function in the excision of lesions from the sensorimotor region. J Neurosurg 61:10471054, 1984

  • 20

    Grondin R, , Chuang S, , Otsubo H, , Holowka S, , Snead OC III, & Raybaud C, et al.: The role of magnetoencephalography in pediatric epilepsy surgery. Childs Nerv Syst 22:779785, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Grover KM, , Bowyer SM, , Rock J, , Rosenblum ML, , Mason KM, & Moran JE, et al.: Retrospective review of MEG visual evoked hemifield responses prior to resection of temporo-parieto-occipital lesions. J Neurooncol 77:161166, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 22

    Hader WJ, , Mackay M, , Otsubo H, , Chitoku S, , Weiss S, & Becker L, et al.: Cortical dysplastic lesions in children with intractable epilepsy: role of complete resection. J Neurosurg 100:2 Suppl 110117, 2004

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23

    Hara K, , Lin FH, , Camposano S, , Foxe DM, , Grant PE, & Bourgeois BF, et al.: Magnetoencephalographic mapping of interictal spike propagation: a technical and clinical report. AJNR Am J Neuroradiol 28:14861488, 2007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 24

    Harvey AS, , Cross JH, , Shinnar S, & Mathern BW: ILAE Pediatric Epilepsy Surgery Survey Taskforce: Defining the spectrum of international practice in pediatric epilepsy surgery patients. Epilepsia 49:146155, 2008

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25

    Hashizume A, , Iida K, , Shirozu H, , Hanaya R, , Kiura Y, & Kurisu K, et al.: Gradient magnetic-field topography for dynamic changes of epileptic discharges. Brain Res 1144:175179, 2007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 26

    Hirata M, , Kato A, , Taniguchi M, , Saitoh Y, , Ninomiya H, & Ihara A, et al.: Determination of language dominance with synthetic aperture magnetometry: comparison with the Wada test. Neuroimage 23:4653, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27

    Holowka SA, , Otsubo H, , Iida K, , Pang E, , Sharma R, & Hunjan A, et al.: Three-dimensionally reconstructed magnetic source imaging and neuronavigation in pediatric epilepsy: technical note. Neurosurgery 55:1226, 2004

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28

    Iida K, , Otsubo H, , Matsumoto Y, , Ochi A, , Oishi M, & Holowka S, et al.: Characterizing magnetic spike sources by using magnetoen-cephalography-guided neuronavigation in epilepsy surgery in pediatric patients. J Neurosurg 102:2 Suppl 187196, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29

    Iwasaki M, , Pestana E, , Burgess RC, , Luders H, , Shamoto H, & Nakasato N: Detection of epileptiform activity by human interpreters: Blinded comparison between electroencephalography and magnetoencephalography. Epilepsia 46:5968, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 30

    Keene DL, , Olds J, & Logan WJ: Functional MRI study of verbal fluency in a patient with subcortical laminar heterotopia. Can J Neurol Sci 31:261264, 2004

  • 31

    Leahy RM, , Mosher JC, , Spencer ME, , Huang MX, & Lewine JD: A study of dipole localization accuracy for MEG and EEG using a human skull phantom. Electroencephalogr Clin Neurophysiol 107:159173, 1998

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 32

    Lesser RP: MEG: good enough. Clin Neurophysiol 115:995997, 2004

  • 33

    Lesser RP, , Luders H, , Morris HH, , Dinner DS, , Klem G, & Hahn J, et al.: Electrical stimulation of Wernicke's area interferes with comprehension. Neurology 36:658663, 1986

  • 34

    Lewine JD, & Orrison WW, Magnetoencephalography and magnetic source imaging. Orrison WW, , Lewine JA, & Hartshorne MF: Functional Brain Imaging St Louis, Mosby Yearbook Inc, 1995. 369417

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 35

    Lopes da Silva FH: What is magnetoencephalography and why it is relevant to neurosurgery?. Adv Tech Stand Neurosurg 30:5167, 2005

  • 36

    Loring DW, , Strauss E, , Hermann BP, , Perrine K, , Trenerry MR, & Barr WB, et al.: Effects of anomalous language representation on neuropsychological performance in temporal lobe epilepsy. Neurology 53:260264, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 37

    Luders H, , Dinner DS, , Lesser RP, & Morris HH: Evoked potentials in cortical localization. J Clin Neurophysiol 3:7584, 1986

  • 38

    Mikuni N, , Nagamine T, , Ikeda A, , Terada K, , Taki W, & Kimura J, et al.: Simultaneous recording of epileptiform discharges by MEG and subdural electrodes in temporal lobe epilepsy. Neuroimage 5:298306, 1997

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 39

    Minassian BA, , Otsubo H, , Weiss S, , Elliott I, , Rutka JT, & Snead OC III: Magnetoencephalographic localization in pediatric epilepsy surgery: comparison with invasive intracranial electroencephalography. Ann Neurol 46:627633, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 40

    Mohamed IS, , Cheyne D, , Gaetz WC, , Otsubo H, , Logan WJ, & Carter Snead O III, et al.: Spatiotemporal patterns of oscillatory brain activity during auditory word recognition in children: A synthetis aperture magnetometry study. Int J Psychophysiol 68:141148, 2008

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 41

    Mohamed IS, , Otsubo H, , Ochi A, , Elliott I, , Donner EJ, & Chuang S, et al.: Utility of magnetoencephalography in the evaluation of recurrent seizures after epilepsy surgery. Epilepsia 48:21502159, 2007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 42

    Munari C, , Broggi G, & Scerrati M: Epilepsy surgery: guidelines for minimum standard equipment and organization. J Neurosurg Sci 44:173176, 2000

  • 43

    Ochi A, & Otsubo H: Magnetoencephalography-guided epilepsy surgery for children with intractable focal epilepsy: SickKids experience. Int J Psychophysiol 68:10110, 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 44

    Ochi A, , Otsubo H, , Iida K, , Oishi M, , Elliott I, & Weiss SK, et al.: Identifying the primary epileptogenic hemisphere from electroencephalographic (EEG) and magnetoencephalographic dipole lateralizations in children with intractable epilepsy. J Child Neurol 20:885892, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 45

    Oishi M, , Kameyama S, , Masuda H, , Tohyama J, , Kanazawa O, & Sasagawa M, et al.: Single and multiple clusters of magnetoencephalographic dipoles in neocortical epilepsy: significance in characterizing the epileptogenic zone. Epilepsia 47:355364, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 46

    Oishi M, , Otsubo H, , Kameyama S, , Wachi M, , Tanaka K, & Masuda H, et al.: Ictal magnetoencephalographic discharges from elementary visual hallucinations of status epilepticus. J Neurol Neurosurg Psychiatry 74:525527, 2003

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 47

    Oishi M, , Otsubo H, , Suyama Y, , Ochi A, , Iida K, & Weiss SK, et al.: Preoperative simulation of intracerebral epileptiform discharges: synthetic aperture magnetometry virtual sensor analysis of inter-ictal magnetoencephalography data. J Neurosurg 105:1 Suppl 4149, 2006

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 48

    Otsubo H, , Ochi A, , Elliott I, , Chuang SH, , Rutka JT, & Jay V, et al.: MEG predicts epileptic zone in lesional extrahippocampal epilepsy: 12 pediatric surgery cases. Epilepsia 42:15231530, 2001

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 49

    Otsubo H, , Oishi M, & Snead OCI, Magnetoencephalography. Miller JW, & Silbergeld DL: Epilepsy Surgery: Principles and Controversies New York, Taylor and Francis Group, 2006. 752767

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 50

    Otsubo H, , Sharma R, , Elliott I, , Holowka S, , Rutka JT, & Snead OC III: Confirmation of two magnetoencephalographic epileptic foci by invasive monitoring from subdural electrodes in an adolescent with right frontocentral epilepsy. Epilepsia 40:608613, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 51

    Pang EW, , Gaetz W, , Otsubo H, , Chuang S, & Cheyne D: Localization of auditory N1 in children using MEG: source modeling issues. Int J Psychophysiol 51:2735, 2003

  • 52

    Papanicolaou AC, , Pazo-Alvarez P, , Castillo EM, , Billingsley-Marshall RL, , Breier JI, & Swank PR, et al.: Functional neuroimaging with MEG: normative language profiles. Neuroimage 33:326342, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 53

    Papanicolaou AC, , Simos PG, , Breier JI, , Zouridakis G, , Willmore LJ, & Wheless JW, et al.: Magnetoencephalographic mapping of the language-specific cortex. J Neurosurg 90:8593, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 54

    Papanicolaou AC, , Simos PG, , Castillo EM, , Breier JI, , Sarkari S, & Pataraia E, et al.: Magnetocephalography: a noninvasive alternative to the Wada procedure. J Neurosurg 100:867876, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 55

    Pataraia E, , Baumgartner C, , Lindinger G, & Deecke L: Magnetoencephalography in presurgical epilepsy evaluation. Neurosurg Rev 25:141161, 2002

  • 56

    Pataraia E, , Simos PG, , Castillo EM, , Billingsley RL, , Sarkari S, & Wheless JW, et al.: Does magnetoencephalography add to scalp video-EEG as a diagnostic tool in epilepsy surgery?. Neurology 62:943948, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 57

    Patil SG, , Cross JH, , Kling Chong W, , Boyd SG, , Harkness WJ, & Neville BG, et al.: Is streamlined evaluation of children for epilepsy surgery possible?. Epilepsia [epub ahead of print] 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 58

    RamachandranNair R, , Otsubo H, , Shroff MM, , Ochi A, , Weiss SK, & Rutka JT, et al.: MEG predicts outcome following surgery for intractable epilepsy in children with normal or non-focal MRI findings. Epilepsia 48:149157, 2007

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 59

    Ressel V, , Wilke M, , Lidzba K, , Lutzenberger W, & Krageloh-Mann I: Increases in language lateralization in normal children as observed using magnetoencephalography. Brain Lang [epub ahead of print] 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 60

    Rosenow F, & Lüders H: Presurgical evaluation of epilepsy. Brain 124:16831700, 2001

  • 61

    Rowley HA, & Roberts TP: Functional localization in magnetoencephalography. Neuroimaging Clin N Am 5:695710, 1995

  • 62

    Rutka JT, , Otsubo H, , Kitano S, , Sakamoto H, , Shirasawa A, & Ochi A, et al.: Utility of digital camera-derived intraoperative images in the planning of epilepsy surgery for children. Neurosurgery 45:11861191, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 63

    Salanova V, , Markand O, & Worth R: Longitudinal follow-up in 145 patients with medically refractory temporal lobe epilepsy treated surgically between 1984 and 1995. Epilepsia 40:14171423, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 64

    Saltzman-Benaiah J, , Scott K, & Smith ML: Factors associated with atypical speech representation in children with intractable epilepsy. Neuropsychologia 41:19671974, 2003

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 65

    Shibasaki H, , Ikeda A, & Nagamine T: Use of magnetoencephalography in the presurgical evaluation of epilepsy patients. Clin Neurophysiol 118:14381448, 2007

  • 66

    Shiraishi H, , Ahlfors SP, , Stufflebeam SM, , Takano K, , Okajima M, & Knake S, et al.: Application of magnetoencephalography in epilepsy patients with widespread spike or slow-wave activity. Epilepsia 46:12641272, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 67

    Snead OC III: Surgical treatment of medically refractory epilepsy in childhood. Brain Dev 23:199207, 2001

  • 68

    Stefan H, , Hummel C, , Scheler G, , Genow A, , Druschky K, & Tilz C, et al.: Magnetic brain source imaging of focal epileptic activity: a synopsis of 455 cases. Brain 126:23962405, 2003

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 69

    Tao JX, , Ray A, , Hawes-Ebersole S, & Ebersole JS: Intracranial EEG substrates of scalp EEG interictal spikes. Epilepsia 46:669676, 2005

  • 70

    Williamson SJ, , Robinson SE, & Kaufman L, Methods and instrumentation for biomagnetism. Atsumi K, , Kotani M, & Ueno S, et al.: Biomagnetism '87 Tokio, Tokio Denki University, 1988. 1825

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 71

    Wood CC, , Spencer DD, , Allison T, , McCarthy G, , Williamson PD, & Goff WR: Localization of human sensorimotor cortex during surgery by cortical surface recording of somatosensory evoked potentials. J Neurosurg 68:99111, 1988

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 72

    Wyler AR, , Hermann BP, & Richey ET: Results of reoperation for failed epilepsy surgery. J Neurosurg 71:815819, 1989

  • 73

    Zentner J, , Hufnagel A, , Wolf HK, , Ostertun B, , Behrens E, & Campos MG, et al.: Surgical treatment of neoplasms associated with medically intractable epilepsy. Neurosurgery 41:378387, 1997

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
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  • Coronal, sagittal, and axial MR images showing examples of MEGSS distribution patterns consisting of MEGSS clusters (closed circles), small clusters (open triangles), and scatters (open squares). The MEGSSs were overlaid on single-plane MR images. Reprinted with permission from Iida K, et al: J Neurosurg 102 (2 Suppl):187–196, 2005.

  • Axial FLAIR MR images showing abnormal signal in the subcortical white matter in the right mesial occipital region (white arrows).

  • Axial T1-weighted MR images showing 4 (left) and 2 (right) of 37 MEG spike sources over the right pari-etooccipital region around the MR imaging abnormality. (Closed triangles represent the location of MEGSSs and tails indicate the orientation of the MEG spike sources). The white arrow indicates extension of focal cortical dysplasia in the right parietal lobe just above the parietooccipital fissure.

  • Left: Intraoperative photograph showing a subdural grid containing 100 electrodes on the right temporoparietooccipital region, 2 depth electrodes to the superior (D31–34) and inferior (D41–44) margins of the clustered MEG spike sources, and 1 strip electrode (S1–4) in the interhemispheric fissure covering the calcarine cortex. Extraoperative electrical stimulation on only 1 electrode (Electrode 11, yellow open circle) demonstrated the hand motor cortex. Somatosensory evoked potential testing using the grid electrodes showed that Electrodes 10–12 and 21 (yellow open squares) represent motor cortex and Electrodes 22 and 34 (green open squares) represent sensory cortex. The ictal onset zone (red squares) was confirmed in the right mesial occipital region (D33, 34) and right parietooccipital junction close to the midline (S1–4). Seizures spread to the lateral parietal and occipital region. The patient underwent a right occipital lobectomy and cortical excision over the right parietooccipital region including the cluster of MEG spike sources and MR imaging lesion (yellow line). Right: A 3D MR image reconstructed from thin-sliced T1-weighted MR images showing a total of 37 MEG spike sources (purple dots). Twenty-six MEG spike sources were clustered in the right occipital region (white arrow). The other 11 scattered MEG spike sources were located in the right temporoparietooccipital region.

  • 1

    Akai T, , Otsubo H, , Pang EW, , Rutka JT, , Chitoku S, & Weiss SK, et al.: Complex central cortex in pediatric patients with malformations of cortical development. J Child Neurol 17:347352, 2002

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Alberstone CD, , Skirboll SL, , Benzel EC, , Sanders JA, , Hart BL, & Baldwin NG, et al.: Magnetic source imaging and brain surgery: presurgical and intraoperative planning in 26 patients. J Neurosurg 92:7990, 2000

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3

    Awad IA, , Nayel MH, & Luders H: Second operation after the failure of previous resection for epilepsy. Neurosurgery 28:510518, 1991

  • 4

    Barkley G, & Baumgartner C: MEG and EEG in epilepsy. J Clin Neurophysiol 20:163178, 2003

  • 5

    Baumgartner C, & Pataraia E: Revisiting the role of magnetoencephalography in epilepsy. Curr Opin Neurol 19:181186, 2006

  • 6

    Bercovici E, , Pang EW, , Sharma R, , Mohamed IS, , Imai K, & Fujimoto A, et al.: Somatosensory-evoked fields on magnetoencephalography for epilepsy infants younger than 4 years with total intravenous anesthesia. Clin Neurophysiol 119:13281334, 2008

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7

    Bowyer SM, , Moran JE, , Weiland BJ, , Mason KM, , Greenwald ML, & Smith BJ, et al.: Language laterality determined by MEG mapping with MR-FOCUSS. Epilepsy Behav 6:235241, 2005

  • 8

    Breier JI, , Castillo EM, , Simos PG, , Billingsley-Marshall RL, , Pataraia E, & Sarkari S, et al.: Atypical language representation in patients with chronic seizure disorder and achievement deficits with magnetoencephalography. Epilepsia 46:540548, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9

    Cohen D: Magnetoencephalography: evidence of magnetic fields produced by alpha-rhythm currents. Science 161:784786, 1968

  • 10

    Cohen D, & Cuffin BN: Demonstration of useful differences between the magnetoencephalogram and electroencephalogram. Electroencephalogr Clin Neurophysiol 56:3851, 1983

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 11

    Cooper R, , Winter AL, , Crow HJ, & Walter WG: Comparison of subcortical, cortical and scalp activity using chronically indwelling electrodes in man. Electroencephalogr Clin Neurophysiol 18:217228, 1965

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    de Jongh A, , de Munck JC, , Goncalvez SI, & Ossenblok P: Differences in MEG/EEG epileptic spike yields explained by regional differences in signal-to-noise ratios. J Clin Neurophysiol 22:153158, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13

    Drake J, , Hoffman HJ, , Kobayashi J, , Hwang P, & Becker LE: Surgical management of children with temporal lobe epilepsy and mass lesions. Neurosurgery 21:792797, 1987

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14

    Ebersole JS, , Squires KC, , Eliashiv SD, & Smith JR: Applications of magnetic source imaging in evaluation of candidates for epilepsy surgery. Neuroimaging Clin N Am 5:267288, 1995

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 15

    Engel J, , Van Ness P, & Rasmussen T, et al.: Outcome with respect to epileptic seizures. Engel J: Surgical Treatment of the Epilepsies ed 2 New York, Raven Press, 1993. 609621

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16

    Gaetz W, , Cheyne D, , Rutka J, , Drake J, , Benifla M, & Strantzas S, et al.: Pre-surgical localization of primary cortex in paediatric patients with brain lesions using spatially filtered MEG. Neurosurgery In press 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Gallen CC, , Schwartz BJ, , Bucholz RD, , Malik G, , Barkley GL, & Smith J, et al.: Presurgical localization of functional cortex using magnetic source imaging. J Neurosurg 82:988994, 1995

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18

    Gallen CC, , Sobel DF, , Waltz T, , Aung M, , Copeland B, & Schwartz BJ, et al.: Noninvasive presurgical neuromagnetic mapping of somatosensory cortex. Neurosurgery 33:260268, 1993

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19

    Gregorie EM, & Goldring S: Localization of function in the excision of lesions from the sensorimotor region. J Neurosurg 61:10471054, 1984

  • 20

    Grondin R, , Chuang S, , Otsubo H, , Holowka S, , Snead OC III, & Raybaud C, et al.: The role of magnetoencephalography in pediatric epilepsy surgery. Childs Nerv Syst 22:779785, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 21

    Grover KM, , Bowyer SM, , Rock J, , Rosenblum ML, , Mason KM, & Moran JE, et al.: Retrospective review of MEG visual evoked hemifield responses prior to resection of temporo-parieto-occipital lesions. J Neurooncol 77:161166, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 22

    Hader WJ, , Mackay M, , Otsubo H, , Chitoku S, , Weiss S, & Becker L, et al.: Cortical dysplastic lesions in children with intractable epilepsy: role of complete resection. J Neurosurg 100:2 Suppl 110117, 2004

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23

    Hara K, , Lin FH, , Camposano S, , Foxe DM, , Grant PE, & Bourgeois BF, et al.: Magnetoencephalographic mapping of interictal spike propagation: a technical and clinical report. AJNR Am J Neuroradiol 28:14861488, 2007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 24

    Harvey AS, , Cross JH, , Shinnar S, & Mathern BW: ILAE Pediatric Epilepsy Surgery Survey Taskforce: Defining the spectrum of international practice in pediatric epilepsy surgery patients. Epilepsia 49:146155, 2008

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25

    Hashizume A, , Iida K, , Shirozu H, , Hanaya R, , Kiura Y, & Kurisu K, et al.: Gradient magnetic-field topography for dynamic changes of epileptic discharges. Brain Res 1144:175179, 2007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 26

    Hirata M, , Kato A, , Taniguchi M, , Saitoh Y, , Ninomiya H, & Ihara A, et al.: Determination of language dominance with synthetic aperture magnetometry: comparison with the Wada test. Neuroimage 23:4653, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27

    Holowka SA, , Otsubo H, , Iida K, , Pang E, , Sharma R, & Hunjan A, et al.: Three-dimensionally reconstructed magnetic source imaging and neuronavigation in pediatric epilepsy: technical note. Neurosurgery 55:1226, 2004

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28

    Iida K, , Otsubo H, , Matsumoto Y, , Ochi A, , Oishi M, & Holowka S, et al.: Characterizing magnetic spike sources by using magnetoen-cephalography-guided neuronavigation in epilepsy surgery in pediatric patients. J Neurosurg 102:2 Suppl 187196, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29

    Iwasaki M, , Pestana E, , Burgess RC, , Luders H, , Shamoto H, & Nakasato N: Detection of epileptiform activity by human interpreters: Blinded comparison between electroencephalography and magnetoencephalography. Epilepsia 46:5968, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 30

    Keene DL, , Olds J, & Logan WJ: Functional MRI study of verbal fluency in a patient with subcortical laminar heterotopia. Can J Neurol Sci 31:261264, 2004

  • 31

    Leahy RM, , Mosher JC, , Spencer ME, , Huang MX, & Lewine JD: A study of dipole localization accuracy for MEG and EEG using a human skull phantom. Electroencephalogr Clin Neurophysiol 107:159173, 1998

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 32

    Lesser RP: MEG: good enough. Clin Neurophysiol 115:995997, 2004

  • 33

    Lesser RP, , Luders H, , Morris HH, , Dinner DS, , Klem G, & Hahn J, et al.: Electrical stimulation of Wernicke's area interferes with comprehension. Neurology 36:658663, 1986

  • 34

    Lewine JD, & Orrison WW, Magnetoencephalography and magnetic source imaging. Orrison WW, , Lewine JA, & Hartshorne MF: Functional Brain Imaging St Louis, Mosby Yearbook Inc, 1995. 369417

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 35

    Lopes da Silva FH: What is magnetoencephalography and why it is relevant to neurosurgery?. Adv Tech Stand Neurosurg 30:5167, 2005

  • 36

    Loring DW, , Strauss E, , Hermann BP, , Perrine K, , Trenerry MR, & Barr WB, et al.: Effects of anomalous language representation on neuropsychological performance in temporal lobe epilepsy. Neurology 53:260264, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 37

    Luders H, , Dinner DS, , Lesser RP, & Morris HH: Evoked potentials in cortical localization. J Clin Neurophysiol 3:7584, 1986

  • 38

    Mikuni N, , Nagamine T, , Ikeda A, , Terada K, , Taki W, & Kimura J, et al.: Simultaneous recording of epileptiform discharges by MEG and subdural electrodes in temporal lobe epilepsy. Neuroimage 5:298306, 1997

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 39

    Minassian BA, , Otsubo H, , Weiss S, , Elliott I, , Rutka JT, & Snead OC III: Magnetoencephalographic localization in pediatric epilepsy surgery: comparison with invasive intracranial electroencephalography. Ann Neurol 46:627633, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 40

    Mohamed IS, , Cheyne D, , Gaetz WC, , Otsubo H, , Logan WJ, & Carter Snead O III, et al.: Spatiotemporal patterns of oscillatory brain activity during auditory word recognition in children: A synthetis aperture magnetometry study. Int J Psychophysiol 68:141148, 2008

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 41

    Mohamed IS, , Otsubo H, , Ochi A, , Elliott I, , Donner EJ, & Chuang S, et al.: Utility of magnetoencephalography in the evaluation of recurrent seizures after epilepsy surgery. Epilepsia 48:21502159, 2007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 42

    Munari C, , Broggi G, & Scerrati M: Epilepsy surgery: guidelines for minimum standard equipment and organization. J Neurosurg Sci 44:173176, 2000

  • 43

    Ochi A, & Otsubo H: Magnetoencephalography-guided epilepsy surgery for children with intractable focal epilepsy: SickKids experience. Int J Psychophysiol 68:10110, 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 44

    Ochi A, , Otsubo H, , Iida K, , Oishi M, , Elliott I, & Weiss SK, et al.: Identifying the primary epileptogenic hemisphere from electroencephalographic (EEG) and magnetoencephalographic dipole lateralizations in children with intractable epilepsy. J Child Neurol 20:885892, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 45

    Oishi M, , Kameyama S, , Masuda H, , Tohyama J, , Kanazawa O, & Sasagawa M, et al.: Single and multiple clusters of magnetoencephalographic dipoles in neocortical epilepsy: significance in characterizing the epileptogenic zone. Epilepsia 47:355364, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 46

    Oishi M, , Otsubo H, , Kameyama S, , Wachi M, , Tanaka K, & Masuda H, et al.: Ictal magnetoencephalographic discharges from elementary visual hallucinations of status epilepticus. J Neurol Neurosurg Psychiatry 74:525527, 2003

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 47

    Oishi M, , Otsubo H, , Suyama Y, , Ochi A, , Iida K, & Weiss SK, et al.: Preoperative simulation of intracerebral epileptiform discharges: synthetic aperture magnetometry virtual sensor analysis of inter-ictal magnetoencephalography data. J Neurosurg 105:1 Suppl 4149, 2006

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 48

    Otsubo H, , Ochi A, , Elliott I, , Chuang SH, , Rutka JT, & Jay V, et al.: MEG predicts epileptic zone in lesional extrahippocampal epilepsy: 12 pediatric surgery cases. Epilepsia 42:15231530, 2001

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 49

    Otsubo H, , Oishi M, & Snead OCI, Magnetoencephalography. Miller JW, & Silbergeld DL: Epilepsy Surgery: Principles and Controversies New York, Taylor and Francis Group, 2006. 752767

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 50

    Otsubo H, , Sharma R, , Elliott I, , Holowka S, , Rutka JT, & Snead OC III: Confirmation of two magnetoencephalographic epileptic foci by invasive monitoring from subdural electrodes in an adolescent with right frontocentral epilepsy. Epilepsia 40:608613, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 51

    Pang EW, , Gaetz W, , Otsubo H, , Chuang S, & Cheyne D: Localization of auditory N1 in children using MEG: source modeling issues. Int J Psychophysiol 51:2735, 2003

  • 52

    Papanicolaou AC, , Pazo-Alvarez P, , Castillo EM, , Billingsley-Marshall RL, , Breier JI, & Swank PR, et al.: Functional neuroimaging with MEG: normative language profiles. Neuroimage 33:326342, 2006

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 53

    Papanicolaou AC, , Simos PG, , Breier JI, , Zouridakis G, , Willmore LJ, & Wheless JW, et al.: Magnetoencephalographic mapping of the language-specific cortex. J Neurosurg 90:8593, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 54

    Papanicolaou AC, , Simos PG, , Castillo EM, , Breier JI, , Sarkari S, & Pataraia E, et al.: Magnetocephalography: a noninvasive alternative to the Wada procedure. J Neurosurg 100:867876, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 55

    Pataraia E, , Baumgartner C, , Lindinger G, & Deecke L: Magnetoencephalography in presurgical epilepsy evaluation. Neurosurg Rev 25:141161, 2002

  • 56

    Pataraia E, , Simos PG, , Castillo EM, , Billingsley RL, , Sarkari S, & Wheless JW, et al.: Does magnetoencephalography add to scalp video-EEG as a diagnostic tool in epilepsy surgery?. Neurology 62:943948, 2004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 57

    Patil SG, , Cross JH, , Kling Chong W, , Boyd SG, , Harkness WJ, & Neville BG, et al.: Is streamlined evaluation of children for epilepsy surgery possible?. Epilepsia [epub ahead of print] 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 58

    RamachandranNair R, , Otsubo H, , Shroff MM, , Ochi A, , Weiss SK, & Rutka JT, et al.: MEG predicts outcome following surgery for intractable epilepsy in children with normal or non-focal MRI findings. Epilepsia 48:149157, 2007

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 59

    Ressel V, , Wilke M, , Lidzba K, , Lutzenberger W, & Krageloh-Mann I: Increases in language lateralization in normal children as observed using magnetoencephalography. Brain Lang [epub ahead of print] 2008

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 60

    Rosenow F, & Lüders H: Presurgical evaluation of epilepsy. Brain 124:16831700, 2001

  • 61

    Rowley HA, & Roberts TP: Functional localization in magnetoencephalography. Neuroimaging Clin N Am 5:695710, 1995

  • 62

    Rutka JT, , Otsubo H, , Kitano S, , Sakamoto H, , Shirasawa A, & Ochi A, et al.: Utility of digital camera-derived intraoperative images in the planning of epilepsy surgery for children. Neurosurgery 45:11861191, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 63

    Salanova V, , Markand O, & Worth R: Longitudinal follow-up in 145 patients with medically refractory temporal lobe epilepsy treated surgically between 1984 and 1995. Epilepsia 40:14171423, 1999

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 64

    Saltzman-Benaiah J, , Scott K, & Smith ML: Factors associated with atypical speech representation in children with intractable epilepsy. Neuropsychologia 41:19671974, 2003

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 65

    Shibasaki H, , Ikeda A, & Nagamine T: Use of magnetoencephalography in the presurgical evaluation of epilepsy patients. Clin Neurophysiol 118:14381448, 2007

  • 66

    Shiraishi H, , Ahlfors SP, , Stufflebeam SM, , Takano K, , Okajima M, & Knake S, et al.: Application of magnetoencephalography in epilepsy patients with widespread spike or slow-wave activity. Epilepsia 46:12641272, 2005

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 67

    Snead OC III: Surgical treatment of medically refractory epilepsy in childhood. Brain Dev 23:199207, 2001

  • 68

    Stefan H, , Hummel C, , Scheler G, , Genow A, , Druschky K, & Tilz C, et al.: Magnetic brain source imaging of focal epileptic activity: a synopsis of 455 cases. Brain 126:23962405, 2003

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 69

    Tao JX, , Ray A, , Hawes-Ebersole S, & Ebersole JS: Intracranial EEG substrates of scalp EEG interictal spikes. Epilepsia 46:669676, 2005

  • 70

    Williamson SJ, , Robinson SE, & Kaufman L, Methods and instrumentation for biomagnetism. Atsumi K, , Kotani M, & Ueno S, et al.: Biomagnetism '87 Tokio, Tokio Denki University, 1988. 1825

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 71

    Wood CC, , Spencer DD, , Allison T, , McCarthy G, , Williamson PD, & Goff WR: Localization of human sensorimotor cortex during surgery by cortical surface recording of somatosensory evoked potentials. J Neurosurg 68:99111, 1988

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 72

    Wyler AR, , Hermann BP, & Richey ET: Results of reoperation for failed epilepsy surgery. J Neurosurg 71:815819, 1989

  • 73

    Zentner J, , Hufnagel A, , Wolf HK, , Ostertun B, , Behrens E, & Campos MG, et al.: Surgical treatment of neoplasms associated with medically intractable epilepsy. Neurosurgery 41:378387, 1997

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation

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