Abstracts

Noninvasive preoperative localization techniques are sought to replace all invasive extraoperative procedures in neurosurgical patients with medically intractable epilepsy. In attempts to bypass more invasive methods, such as intracranial long term monitoring (ILTM), yet maintain precision and accuracy in detecting epileptic foci, magnetoencephalography (MEG) has shown promise as a means of lateralizing and localizing epileptic foci. This retrospective analysis of 35 patients studied the correlation between localization capabilities of MEG and surgical outcome in patients with intractable mesial temporal lobe epilepsy (MTLE). MEG was performed in 105 patients with localization-related epilepsy. Of these, 35 patients (20F;15M) aged 13 - 70 years, underwent anterior temporal lobe resections with amygdalohippocampectomy following ILTM or intraoperative electrocorticography (ECoG). All patients underwent noninvasive long term monitoring, MRI, neuropsychometric testing and Wada study; select patients had ictal SPECT and interictal SPECT performed. Patient outcome was assessed after one year of postoperative follow-up using the Engel criteria. Patients free of disabling seizures (Class I) numbered 23/35 (66%) with the remainder identified as Class II (6%), Class III (20%) and Class IV (9%). Suboptimal surgical outcomes (Class III/IV) occurred in 10/35 patients (29%). Of the 23 Class I outcomes, MEG correctly lateralized the temporal epileptic focus in 15 patients (65%). The predominant MEG spike focus lateralized to the side of the preoperatively determined ictal onset zone in 26 patients (74%) although, of these, 9 had suboptimal surgical outcomes. MEG failed to predict a Class I outcome with sufficient lateralization in 8/35 (23%). Magnetoencephalography, in its present stage of development, serves to provide useful localizing information for ILTM in nonlesional MTLE. Its contributions will be enhanced by improvements in sampling of data.