Abstracts

Rationale: Analysis of selected patients undergoing epilepsy surgery revisions to identify potential predictive factors for epilepsy surgery failures Methods: We conducted a retrospective review of all patients undergoing revision epilepsy surgery at our institution between 2004 and 2006. Special attention was focused on the underlying pathology, extent of preoperative evaluation, as well as localization of the epileptogenic fociResults: We identified 34 patients who underwent revision surgery. Of these patients 21 had lesions with the following neuropathologic diagnoses: 12 neoplasms, 2 migration disorders, 1 hygroma, 1 cyst formation (prior surgical site), 1 tuberous sclerosis, 1 schizencephaly, 1 traumatic and 2 spontaneous hemorrhages (1 angioma and 1 arteriovenous malformation). The remaining 13 patients had non-lesional surgeries, of these 12 were multifocal with extratemporal involvement and only 1 surgery was a single focus operation (repeat frontal lobectomy for a residual frontal lobe focus). All revisions had an intracranial EEG with grid placement as preoperative evaluation. Of the 13 non-lesional surgeries, 10 patients underwent grid placement prior to the failed primary surgery and 8 of these patients had additional seizure foci identified during repeat invasive monitoring, subsequently 2 patients had resections of the residual foci. Three non-lesional cases also had additional foci identified during a 2-stage revision including grid placement. In summary, 11 patients had new foci responsible for seizure recurrence and 8 of those had invasive intracranial work-up prior to both the primary and repeat surgery.Conclusions: The majority of patients analyzed in our sample had revision surgeries related to underlying structural pathology (62%). Almost all of the non-lesional surgeries requiring revision (92%) had large extratemporal multifocal epileptogenic zones suggesting an association with poorer outcomes in these patients. Identification of additional foci in most of our non-lesional epilepsy patients occurred despite a complete work-up before the primary surgery. 72% of those patients had new seizure zones identified by repeat grid evaluation. Given sensitivity of this invasive monitoring, the new epileptic zones likely developed due to progression of the disease. Further research is necessary to determine specific factors in predicting outcomes in patients with large extratemporal multifocal epilepsy surgeries.