Magnetoencephalography indications

Magnetoencephalography (MEG) is a noninvasive technique that is used for presurgical evaluation of children with drug-resistant epilepsy (DRE).

MEG could change the clinical management of children with DRE by directing the placement of intracranial electrodes thereby enhancing their yield. With improved identification of a circumscribed epileptogenic zone, MEG could render more patients as suitable candidates for epilepsy surgery and increase utilization of surgery 1).

Magnetoencephalography (MEG) is valuable for guiding in resective epilepsy surgery. MEG is a useful supplement for patients with MRI-negative epilepsy. MEG can be applied in minimally invasive treatment. MEG clusters can help identify better candidates and provide a valuable target for stereoelectroencephalography guided radiofrequency thermocoagulation, which leads to better outcomes. 2).

Magnetoencephalography and stereoelectroencephalography are often necessary in the course of the non-invasive and invasive presurgical evaluation of challenging patients with drug resistant epilepsy.

Magnetoencephalography (MEG) enables noninvasive detection of interictal spike activity in epilepsy, which can then be localized in three dimensions using magnetic source imaging (MSI) techniques. However, the clinical value of MEG in the presurgical epilepsy evaluation is not fully understood, as studies to date are limited by either a lack of long-term seizure outcomes or a small sample size.

MEG play an additional and valuable role in the localisation of operculo-insular epilepsy for patients with a negative MRI finding 3).

Mapping the MEG spike population is valid for demonstrating the trend of spikes clustering in patients with epilepsy. In addition, comparison of MEG and intracranial electroencephalographic (IEEG) spikes quantitatively may be informative for understanding their relationship 4).

In a study, Murakami et al., aim to examine the significance of magnetoencephalography dipole clusters and their relationship to stereo-electroencephalography findings, area of surgical resection, and seizure outcome. They also aim to define the positive and negative predictors based on magnetoencephalography dipole cluster characteristics pertaining to seizure-freedom. Included in this retrospective study were a consecutive series of 50 patients who underwent magnetoencephalography and stereo-electroencephalography at the Cleveland Clinic Epilepsy Center.

Interictal magnetoencephalography localization was performed using a single equivalent current dipole model. Magnetoencephalography dipole clusters were classified based on tightness and orientation criteria. Magnetoencephalography dipole clusters, stereo-electroencephalography findings and area of resection were reconstructed and examined in the same space using the patient's own magnetic resonance imaging scan. Seizure outcomes at 1 year post-operative were dichotomized into seizure-free or not seizure-free. We found that patients in whom the magnetoencephalography clusters were completely resected had a much higher chance of seizure-freedom compared to the partial and no resection groups (P = 0.007). Furthermore, patients had a significantly higher chance of being seizure-free when stereo-electroencephalography completely sampled the area identified by magnetoencephalography as compared to those with incomplete or no sampling of magnetoencephalography results (P = 0.012). Partial concordance between magnetoencephalography and interictal or ictal stereo-electroencephalography was associated with a much lower chance of seizure freedom as compared to the concordant group (P = 0.0075). Patients with one single tight cluster on magnetoencephalography were more likely to become seizure-free compared to patients with a tight cluster plus scatter (P = 0.0049) or patients with loose clusters (P = 0.018). Patients whose magnetoencephalography clusters had a stable orientation perpendicular to the nearest major sulcus had a better chance of seizure-freedom as compared to other orientations (P = 0.042). Our data demonstrate that stereo-electroencephalography exploration and subsequent resection are more likely to succeed, when guided by positive magnetoencephalography findings. As a corollary, magnetoencephalography clusters should not be ignored when planning the stereo-electroencephalography strategy. Magnetoencephalography tight cluster and stable orientation are positive predictors for a good seizure outcome after resective surgery, whereas the presence of scattered sources diminishes the probability of favourable outcomes. The concordance pattern between magnetoencephalography and stereo-electroencephalography is a strong argument in favour of incorporating localization with non-invasive tools into the process of presurgical evaluation before actual placement of electrodes 5).

Englot et al., performed a retrospective cohort study of patients with focal epilepsy who received MEG for interictal spike mapping followed by surgical resection at our institution.

They studied 132 surgical patients, with mean postoperative follow-up of 3.6 years (minimum 1 year). Dipole source modeling was successful in 103 patients (78%), whereas no interictal spikes were seen in others. Among patients with successful dipole modeling, MEG findings were concordant with and specific to the following: (1) the region of resection in 66% of patients, (2) invasive electrocorticography (ECoG) findings in 67% of individuals, and (3) the magnetic resonance imaging (MRI) abnormality in 74% of cases. MEG showed discordant lateralization in ~5% of cases. After surgery, 70% of all patients achieved seizure freedom (Engel class I outcome). Whereas 85% of patients with concordant and specific MEG findings became seizure-free, this outcome was achieved by only 37% of individuals with MEG findings that were nonspecific to or discordant with the region of resection (χ(2) = 26.4, p < 0.001). MEG reliability was comparable in patients with or without localized scalp electroencephalography (EEG), and overall, localizing MEG findings predicted seizure freedom with an odds ratio of 5.11 (95% confidence interval [CI] 2.23-11.8).

MEG is a valuable tool for noninvasive interictal spike mapping in epilepsy surgery, including patients with nonlocalized findings receiving long-term EEG monitoring, and localization of the epileptogenic zone using MEG is associated with improved seizure outcomes 6).

In a study, Schönherr et al., use a novel automated method for localization and quantitative comparison of magnetoencephalographic (MEG) delta activity in patients with and without recurrent seizures after epilepsy surgery as well as healthy controls.

They identified the generators of delta activity by source location in frequency domain between 1 and 4 Hz in spontaneous MEG data. Comparison with healthy control subjects by z-transform emphasized relative changes of activation in patients. The individual results were compared to spike localizations and statistical group analysis was performed. Additionally, MEG results were compared to 1-4 Hz activity in invasive EEG (iEEG) in two patients, in whom this data was available.

Patients with recurrent seizures exhibited significantly increased focal MEG delta activity both in comparison to healthy controls and seizure free patients. This slow activity showed a correlation to interictal epileptic activity and was not explained by consequences of the resection alone. In two patients with iEEG, iEEG analysis was concordant with the MEG findings.

The quantity of delta activity could be used as a diagnostic marker for recurrent seizures. The close relation to epileptic spike localizations and the resection volume of patients with successful second surgery imply involvement in seizure recurrence. This initial evidence suggests a potential application in the planning of second epilepsy surgery 7).

Otsubo H, Ogawa H, Pang E, Wong SM, Ibrahim GM, Widjaja E. A review of magnetoencephalography use in pediatric epilepsy: an update on best practice. Expert Rev Neurother. 2021 Apr 4:1-16. doi: 10.1080/14737175.2021.1910024. Epub ahead of print. PMID: 33780318.
Gao R, Yu T, Xu C, Zhang X, Yan X, Ni D, Zhang X, Ma K, Qiao L, Zhu J, Wang X, Ren Z, Zhang X, Zhang G, Li Y. The value of magnetoencephalography for stereo-EEG-guided radiofrequency thermocoagulation in MRI-negative epilepsy. Epilepsy Res. 2020 Mar 20;163:106322. doi: 10.1016/j.eplepsyres.2020.106322. [Epub ahead of print] PubMed PMID: 32278277.
Yu T, Ni D, Zhang X, Wang X, Qiao L, Zhou X, Wang Y, Li Y, Zhang G. The role of magnetoencephalography in the presurgical evaluation of patients with MRI-negative operculo-insular epilepsy. Seizure. 2018 Aug 13;61:104-110. doi: 10.1016/j.seizure.2018.07.005. [Epub ahead of print] PubMed PMID: 30125861.
Tanaka N, Papadelis C, Tamilia E, Madsen JR, Pearl PL, Stufflebeam SM. Magnetoencephalographic Mapping of Epileptic Spike Population Using Distributed Source Analysis: Comparison With Intracranial Electroencephalographic Spikes. J Clin Neurophysiol. 2018 Apr 27. doi: 10.1097/WNP.0000000000000476. [Epub ahead of print] PubMed PMID: 29746391.
Murakami H, Wang ZI, Marashly A, Krishnan B, Prayson RA, Kakisaka Y, Mosher JC, Bulacio J, Gonzalez-Martinez JA, Bingaman WE, Najm IM, Burgess RC, Alexopoulos AV. Correlating magnetoencephalography to stereo-electroencephalography in patients undergoing epilepsy surgery. Brain. 2016 Aug 26. pii: aww215. [Epub ahead of print] PubMed PMID: 27567464.
Englot DJ, Nagarajan SS, Imber BS, Raygor KP, Honma SM, Mizuiri D, Mantle M, Knowlton RC, Kirsch HE, Chang EF. Epileptogenic zone localization using magnetoencephalography predicts seizure freedom in epilepsy surgery. Epilepsia. 2015 Jun;56(6):949-58. doi: 10.1111/epi.13002. PubMed PMID: 25921215; PubMed Central PMCID: PMC4457690.
Schönherr M, Stefan H, Hamer HM, Rössler K, Buchfelder M, Rampp S. The delta between postoperative seizure freedom and persistence: Automatically detected focal slow waves after epilepsy surgery. Neuroimage Clin. 2016 Dec 5;13:256-263. doi: 10.1016/j.nicl.2016.12.001. PubMed PMID: 28018852.
  • magnetoencephalography_indications.txt
  • Last modified: 2021/04/07 20:43
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