Abstracts

The lateralization and localization of partial seizures, particularly in extratemporal epilepsy syndromes, remains difficult despite improved diagnostic imaging and electroencephalographic techniques. Magnetic source imaging (MSI) is increasingly employed in the presurgical evaluation. This study retrospectively examines the positive predictive value (PPV) of MSI for lateralizing the epileptogenic zone., All epilepsy surgical cases performed after the availability of MSI (4-D Neuroimaging, equivalent current source dipole localization) at our center were identified. 163 surgeries in 152 patients were performed. 73 patients had a diagnostic pre-operative MSI. Results were available to the epilepsy team prior to surgery; however the MSI results did not directly affect the resection. We compared MSI lateralization to the ICEEG lateralization and resection. These results were reviewed in the context of the surgical outcome for patients with more than six months of post-surgical follow-up., 12 of the 73 patients did not have resections due to non-lateralizable or non-localizable seizures or because their implants were diagnostic bilateral strip surveys. 30 patients had resections limited to the temporal lobe (4 with focal tumors). 3 patients had frontal tumors. 10 patients had multi-focal lesions secondary to tuberous sclerosis complex. The MSI was normal in 9 patients. Of those with an abnormal MSI, 39 had unilateral abnormalities ipsilateral to the resection and 6 had abnormalities limited to the contralateral hemisphere. 19 patients had bilateral findings, with 10 demonstrating a clear predominance ipsilateral to the resection. 40/61 patients undergoing resections had six or more months of follow-up. The PPV for MSI lateralization is shown in the table below.[table1], This retrospective analysis demonstrates both the validity of MSI for lateralizing the epileptogenic zone as well as the method[apos]s limitations; the specificity of the MSI technique for predicting the epileptogenic zone cannot exceed its ability to lateralize correctly. Thus, clinicians should interpret the MSI in the context of other presurgical studies, rather than rely on it as an independent predictor of the epileptogenic zone., (Supported by FACES.)