The presence of short and sharp MEG spikes implies focal cortical dysplasia.

PURPOSE: This study focused on the characteristic needle-like epileptic spikes of short duration and steep shape seen on magnetoencephalography (MEG) in patients diagnosed with focal cortical dysplasia (FCD) morphologically. We aimed to validate the analysis of MEG spike morphology as a noninvasive method of identifying the presence and location of FCD. METHODS: MEG was collected by 204-channel helmet-shaped gradiometers. We analyzed MEG spike sources for 282 patients with symptomatic localization-related epilepsy. MEG showed clustered equivalent current dipoles when superimposed on their three-dimensional-magnetic resonance images (MRI) in 85 patients. Fifty-seven patients were excluded from our study, because they had destructive brain lesions or an insufficient number of spikes for statistical analysis. Twenty-eight patients (18 males, 10 females; aged 1-34 years) were finally matched to our inclusion criteria, and were categorized into three groups: FCD (7 patients), non-FCD (10 patients), and non-lesion (11 patients), based on the MRI findings. We measured the duration, amplitude, and tilt manually for at least 15 spikes per patient, and compared the three groups using a one-way analysis of variance, followed by the Tukey test when statistically significant (p < 0.05). In 17 patients with visible MRI lesions, we investigated the correlation between the depth of the lesion and the tilt using the Pearson product moment correlation. RESULTS: The average spike duration was significantly shorter in the FCD and non-lesion groups than in the non-FCD group (p < 0.05). The average amplitude was not significantly different between the three groups. The average spike tilt was significantly steeper in the FCD group than in the non-FCD group (p = 0.0058). There was no significant difference between FCD and non-lesion patients in both duration and tilt. Our additional study revealed a significant negative correlation between the depth of the lesion and the average tilt (p = 0.0009). SIGNIFICANCE: MEG epileptiform discharges of short duration and steep tilt characterize FCD, especially when located at the superficial neocortical gyrus. We speculate that this particular spike morphology results from the intrinsic epileptogenicity of FCD. Morphological analysis of MEG spikes can evaluate the etiology of epileptogenic lesions and detect a strong, localized epileptogenic focus such as that typically observed in FCD.

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.

The applications of time-frequency analyses to ictal magnetoencephalography in neocortical epilepsy.

PURPOSE: Ictal magenetoencephalographic (MEG) discharges convey significant information about ictal onset and propagation, but there is no established method for analyzing ictal MEG. This study sought to clarify the usefulness of time-frequency analyses using short-time Fourier transform (STFT) for ictal onset and propagation of ictal MEG activity in patients with neocortical epilepsy. METHODS: Four ictal MEG discharges in two patients with perirolandic epilepsy and one with frontal lobe epilepsy (FLE) were evaluated by time-frequency analyses using STFT. Prominent oscillation bands were collected manually and the magnitudes of those specific bands were superimposed on individual 3D-magnetic resonance images. RESULTS: STFT showed specific rhythmic activities from alpha to beta bands at the magnetological onset in all four ictal MEG records. Those activities were located at the vicinity of interictal spike sources, as estimated by the single dipole method (SDM), and two of the four ictal rhythmic activities promptly propagated to ipsilateral or bilateral cerebral cortices. The patients with FLE and perirolandic epilepsy underwent frontal lobectomy and resection of primary motor area, respectively including the origin of high-magnitude areas of a specific band indicated by STFT, and have been seizure free after the surgery. CONCLUSIONS: STFT for ictal MEG discharges readily demonstrated the ictal onset and propagation. These data were important for decisions on surgical procedure and extent of resection. Ictal MEG analyses using STFT could provide a powerful tool for noninvasive evaluation of ictal onset zone.

MEG time-frequency analyses for pre- and post-surgical evaluation of patients with epileptic rhythmic fast activity.

PURPOSE: To evaluate the effectiveness of surgery for epilepsy, we analyzed rhythmic fast activity by magnetoencephalography (MEG) before and after surgery using time-frequency analysis. To assess reliability, the results obtained by pre-surgical MEG and intraoperative electrocorticography were compared. METHODS: Four children with symptomatic localization-related epilepsy caused by circumscribed cortical lesion were examined in the present study using 204-channel helmet-shaped MEG with a sampling rate of 600Hz. One patient had dysembryoplastic neuroepithelial tumor (DNT) and three patients had focal cortical dysplasia (FCD). Aberrant areas were superimposed, to reconstruct 3D MRI images, and illustrated as moving images. RESULTS: In three patients, short-time Fourier transform (STFT) analyses of MEG showed rhythmic activities just above the lesion with FCD and in the vicinity of DNT. In one patient with FCD in the medial temporal lobe, rhythmic activity appeared in the ipsilateral frontal lobe and temporal lateral aspect. These findings correlate well with the results obtained by intraoperative electrocorticography. After the surgery, three patients were relieved of their seizures, and the area of rhythmic MEG activity disappeared or become smaller. One patient had residual rhythmic MEG activity, and she suffered from seizure relapse. CONCLUSION: Time-frequency analyses using STFT successfully depicted MEG rhythmic fast activity, and would provide valuable information for pre- and post-surgical evaluations to define surgical strategies for patients with epilepsy.