Source localization in magnetoencephalography to identify epileptogenic foci

Reinterpretation of magnetic resonance imaging findings with magnetoencephalography can improve the accuracy of detecting epileptogenic cortical lesions

OBJECTIVE

This study examined whether the application of magnetoencephalography (MEG) to interpret magnetic resonance imaging (MRI) findings can aid the diagnosis of intractable epilepsy caused by organic brain lesions.

METHODS

This study included 51 patients with epilepsy who had MEG clusters but whose initial MRI findings were interpreted as being negative for organic lesions. Three board-certified radiologists reinterpreted the MRI findings, utilizing the MEG findings as a guide. The degree to which the reinterpretation of the imaging results identified an organic lesion was rated on a 5-point scale.

RESULTS

Reinterpretation of the MRI data with MEG guidance helped detect an abnormality by at least one radiologist in 18 of the 51 patients (35.2%) with symptomatic localization-related epilepsy. A surgery was performed in 7 of the 51 patients, and histopathological analysis results identified focal cortical dysplasia in 5 patients (Ia: 1, IIa: 2, unknown: 2), hippocampal sclerosis in 1 patient, and dysplastic neurons/gliosis in 1 patient.

CONCLUSIONS

The results of this study highlight the potential diagnostic applications of MEG to detect organic epileptogenic lesions, particularly when radiological visualization is difficult with MRI alone.

Source localization of the seizure onset zone from ictal EEG/MEG data

INTRODUCTION

Surgical treatment of drug-resistant epilepsy relies on the identification of the seizure onset zone (SOZ) and often requires intracranial EEG (iEEG). We have developed a new approach for non-invasive magnetic and electric source imaging of the SOZ (MSI-SOZ and ESI-SOZ) from ictal magnetoencephalography (MEG) and EEG recordings, using wavelet-based Maximum Entropy on the Mean (wMEM) method. We compared the performance of MSI-SOZ and ESI-SOZ with interictal spike source localization (MSI-spikes and ESI-spikes) and clinical localization of the SOZ (i.e., based on iEEG or lesion topography, denoted as clinical-SOZ).

METHODS

A total of 46 MEG or EEG seizures from 13 patients were analyzed. wMEM was applied around seizure onset, centered on the frequency band showing the strongest power change. Principal component analysis applied to spatiotemporal reconstructed wMEM sources (0.4-1 s around seizure onset) identified the main spatial pattern of ictal oscillations. Qualitative sublobar concordance and quantitative measures of distance and spatial overlaps were estimated to compare MSI/ESI-SOZ with MSI/ESI-Spikes and clinical-SOZ.

RESULTS

MSI/ESI-SOZ were concordant with clinical-SOZ in 81% of seizures (MSI 90%, ESI 64%). MSI-SOZ was more accurate and identified sources closer to the clinical-SOZ (P = 0.012) and to MSI-Spikes (P = 0.040) as compared with ESI-SOZ. MSI/ESI-SOZ and MSI/ESI-Spikes did not differ in terms of concordance and distance from the clinical-SOZ.

CONCLUSIONS

wMEM allows non-invasive localization of the SOZ from ictal MEG and EEG. MSI-SOZ performs better than ESI-SOZ. MSI/ESI-SOZ can provide important additional information to MSI/ESI-Spikes during presurgical evaluation. Hum Brain Mapp 37:2528-2546, 2016. © 2016 Wiley Periodicals, Inc.

Advantageous information provided by magnetoencephalography for patients with neocortical epilepsy

PURPOSE

We evaluated whether magnetoencephalography (MEG), in addition to surgery, was valuable for the diagnosis and management of epileptic syndromes in patients with neocortical epilepsy (NE).

METHODS

We studied MEG in 73 patients (29 females; aged 1-26years; mean 10.3years) for the clinical diagnosis of epilepsy and for preoperative evaluation. MEG data were recorded by 204-channel whole head gradiometers with a 600Hz sampling rate. MEG spike sources were localized on magnetic resonance images (MRI) using a single dipole model to project equivalent current dipoles.

RESULTS

MEG localized an epileptic focus with single clustered dipoles in 24 (33%) of 73 NE patients: 16 (25%) of 64 symptomatic localization-related epilepsy (SLRE) patients and eight (89%) of nine idiopathic localization-related epilepsy (ILRE) patients. MEG provided advantageous information in 12 (50%) of 24 patients with clustered dipoles and confirmed the diagnosis in the remaining 12 (50%). Furthermore, the use of MEG resulted in changes to surgical treatments in nine (38%) patients and in medical management in eight (33%). MEG confirmed the diagnosis in eight (16%) of 49 patients with scattered dipoles. MRI identified a single lesion (28 patients, 38%), multiple lesions (5, 7%), and no lesion (40, 55%). MRI provided confirming information in 19 of 28 patients with a single lesion and 18 of them required surgical resections. MRI did not provide any supportive information in 54 (74%) patients with a single (9), multiple (5) and no lesion (40).

CONCLUSION

Our study shows that MEG provides fundamental information to aid the choice of diagnostic and therapeutic procedures including changes in medication in addition to surgical treatments for NE.

Magnetoencephalography in pediatric epilepsy

Magnetoencephalography (MEG) records the magnetic field generated by electrical activity of cortical neurons. The signal is not distorted or attenuated, and it is contactless recording that can be performed comfortably even for longer than an hour. It has excellent and decent temporal resolution, especially when it is combined with the patient's own brain magnetic resonance imaging (magnetic source imaging). Data of MEG and electroencephalography are not mutually exclusive and it is recorded simultaneously and interpreted together. MEG has been shown to be useful in detecting the irritative zone in both lesional and nonlesional epilepsy surgery. It has provided valuable and additive information regarding the lesion that should be resected in epilepsy surgery. Better outcomes in epilepsy surgery were related to the localization of the irritative zone with MEG. The value of MEG in epilepsy surgery is recruiting more patients to epilepsy surgery and providing critical information for surgical planning. MEG cortical mapping is helpful in younger pediatric patients, especially when the epileptogenic zone is close to the eloquent cortex. MEG is also used in both basic and clinical research of epilepsy other than surgery. MEG is a valuable diagnostic modality for diagnosis and treatment, as well as research in epilepsy.