Abstracts

Rationale: Despite significant advances in MRI techniques intracranial EEG (iEEG) has remained the gold standard tool for precise localization of the seizure generator. Here, we report our experience with iEEG and surgical outcomes. Methods: We retrospectively reviewed 66 consecutive admissions for intracranial monitoring in Calgary epilepsy program from January 2009 to December 2013. The seizure onsets were defined focal (in one or two contiguous recording contacts), regional (in one or two contiguous electrodes), lateralized and diffuse. We used Engel classification for seizure outcomes. All patients except one had at least 1 year follow-up. Results: 63 patients, with a mean age of 32.8 years (14.8- 59.3) and the mean duration of epilepsy of 17.8 years (3.0-53.2) had 66 iEEGs. The mean length of stay was 11.7 days (range 3-30) and the average number of the recorded seizures per patient was 27.6 (Range 1-300) with a median of 7.5. Thirty-one patients had a lesion on MRI brain. Twenty-two of these patients had focal seizure onsets, 17 of whom had epilepsy surgery with class I outcomes in 14, and class II in 2. The remaining patients had class II outcome on 6 months follow up. Five patients despite focal seizure onset and MRI lesion did not have any surgical intervention due to risk of neurological deficits. Nine patients with MRI lesion had regional seizure onsets in 4, lateralized in 2 and diffuse in 3. Two patients with regional and 2 with lateralized seizure onsets had surgery with class I and IV outcomes respectively. Thirty-two patients had no MRI lesion from whom, 16 had focal seizure onsets but due to risk of neurological deficit surgery was done in 8 with class I outcome in 4, class II in 2, and class IV in 2. Two patients with regional seizure onsets had surgery with class I and IV outcomes. Four patients with lateralized seizure onset had surgery, based on the other data, with class I outcomes in 1, class II in 1, and class III in 2. The remaining 10 patients with diffuse seizure onset did not have surgery. There were 9 (14%) recorded complications that included 3 scalp haematoma, 2 subdural haematoma,1 empyema, 1 subdural hygroma and 2 focal intraparenchymal hemorrhage. None of patients had any permanent neurological deficit. Conclusions: 35 of 63 patients evaluated by iEEG had epilepsy surgeries from whom 22 became seizure free. The best predictors of class I outcome were iEEG focal seizure onset (p value = 0.12 , 18 focal vs 4 non-focal) and brain MRI lesion (p value = 0.07, 16 lesional vs 6 nonlesional). The procedure was relatively safe with no permanent neurological deficit or death.