Abstracts

Rationale: Systemically reviewing structural images of epilepsy patients (1) is extremely important to identify epileptogenic structural focus/foci reducing the rate of "MRI normal" cases. Neurophysiological tools, such as EEG and MEG/MSI, reflect the direct measure of epilepsy. Once the region of epileptic electromagnetic signal is identified then repeat review of imaging may identify potential areas of structural abnormality that was previously overlooked (2). We sequentially reviewed 200 patients who had MEG/MSI presurgical evaluation recently.

Methods: Sixty-eight out of 200 patients were reported with “non-lesional” MRI. There are 31 female, 37 male, aging 3 to 52 yrs (median 18 years). MEGs were recorded with a 148-MEG channel whole-head system housed in a magnetically shielded room, scalp EEG was recorded simultaneously. Interictal epileptiform discharges of EEG/MEG were reviewed and identified by epileptologists. Single equivalent current dipole and current density modelling were applied. Interictal/ictal magnetic fields were superimposed onto a 3D T1 weighted MR series. The MEG/EEG and MR images were processed and registered with Curry 8 Software (Compumedics Inc, Charlette, NC). MRIs were reassessed systemically by a radiologist with epilepsy imaging experiences (WZ) with special attention on MSI locations.

Results: Re-review of the MRIs revealed subtle findings in 42/68 patients. Eighteen patients were found with abnormal/rare variation changes of sulcation/gyration pattern without blurred gray-white matter or thickening of cortex. Ten with possible FCD with appearances of blurred gray-white matter, thickening gray matter. Another 8 patients with focal atrophic changes. Four with anterior temporal encephalocele, two with MTS or mesial signal change. Of the 42 with subtle MRI findings the ten patients undergone invasive EEG evaluation confirmed the epileptogenic zone/s. Four patients underwent resective surgery, one patient with RNS implantation. Two of temporal encephalocele were confirmed, the other 2 patients with gliosis histologically. Three patients have been seizure free (3, 22, 22 months follow-up) since resective surgery, one is undergoing re-evaluation of his breakthrough auras currently (22 months). The RNS patient is improved significantly (16 months). The rest of patients are being evaluated/pending for surgery or follow-up with other institutions.

Figure. A 12-year-old male patient who underwent MSI and SEEG evaluation: A. A cluster of MEG dipoles noted at left frontal region on this T1 axial image as yellow dots; B. Re-review of his MRI reveals an abnormal gyration/sulcation pattern in the overlapping area, but without blurred grey-white matter junction, thickening cortex and signal intensity changes.

Conclusions: With our limited data, we conclude that 1. MSI should be considered as a routine test in “non-lesional” epilepsy for presurgical evaluation; 2. Guided by MSI epileptogenic localization, re-evaluation of structural imaging may re-categorize the “non-lesional” to “lesional”; 3. Abnormal sulcation/gyration pattern ought to be paid more attention in presurgical evaluation. Further research is needed for this entity.

Funding: Please list any funding that was received in support of this abstract.: N/A.