Abstracts

Surgery for bilateral temporal lobe epilepsy (Bi-TLE), herein defined as seizures arising independently from both temporal lobes, has been demonstrated to have poor efficacy. However, lateralized MRI abnormality and a preponderance of interictal spikes on EEG have been identified as factors for good surgical outcome. Ictal EEG findings are also a decisive factor for determining the resection side. Predominant ictal onset side (PIOS) is considered to be a direct measure of laterality of ictogenisity, however, this has yet to be quantitative analyzed. In this study, we reviewed our surgical series of Bi-TLE patients and determined the correlation between quantitatively assessed PIOS and postoperative outcome., We analyzed data from 23 patients with Bi-TLE who had undergone anterior temporal lobectomy. Patients[apos] ages at the time of the operation ranged from 14 to 55 years (mean 31.2 years). Diagnoses of Bi-TLE were confirmed using subdural electrode recordings, and the side of resection was determined by PIOS. Postoperative seizure outcome was assessed using Engel[apos]s outcome classification between 9 and 161 months (mean 80 months) after surgery. Percentages of ictal onset side calculated on the basis of all recorded seizures and other clinical characteristics were correlated with postoperative seizure outcome., Regarding postoperative seizure outcome, 9 patients (39.1 %) were class I, 8 patients (34.8 %) were class II, and 6 patients (26.1 %) were class III. The following items were found to be statistically significant factors for good surgical outcome: 1) no history of severe encephalitis (p = 0.03), 2) higher percentage of PIOS (class I vs. class II-III, 87.6[plusmn]3.1% vs. 73.7[plusmn]3.3%, p = 0.009), and 3) lateralized lesion (p = 0.01), or absence of bilateral abnormalities on MRI (p = 0.02). Furthermore, multivariate analyses showed that factors 1) and 2) were independent predictors of good outcome., Surgery for Bi-TLE results in a greater reduction of seizures if preoperative evaluations show good predictive factors. In particular, when the percentage of PIOS is greater than 85 %, a more favorable outcome can be obtained.,