Abstracts

Rationale: Non-lesional refractory partial epilepsy refers to the presence of a focal ictal onset zone (IZ), normal conventional brain Magnetic Resonance Imaging (BMRI) and lack of therapeutic response to two anti-epileptic medications (AED). This population is considered a good epilepsy surgery candidate, if the ictal zone is well identified. A precise definition of the IZ is critical for surgical planning. Methods: Our hypothesis is that the IZ, as defined by EEG studies, correlates with abnormalities on a 3T BMRI. We have retrospectively reviewed the medical records of 12 patients that underwent phase I and II comprehensive epilepsy evaluation. In addition, this study has prospectively enrolled 7 patients for a 3T BMRI. Descriptive statistics were performed. Results: Ninety five percent of the subjects are still receiving at least one AED and 69 % receive two or more AED. Age of onset of seizures is in average 15.9 years of age. All subjects have seizure semiology consistent with a partial ictal onset and the most common symptoms are: staring (64%), repetitive vocalizations (21%), head version (16 %), epigastric discomfort (11%), olfactory hallucinations (11%) and D j vu (11%). The average number of seizures per month in the study population was two. Risk factors for epilepsy identified in this cohort are: trauma (32%), genetic predisposition (11%), drug abuse (5%), and stroke (5%). No risk factors were identified in 16% of cases. Lateralization to the left was most commonly seen (42 %) followed by right lateralization (37%) and no lateralization (21 %).Temporal lobe localization occurred in 64% of cases and extra-temporal in 36 %. Neuropsychological assessment revealed an average verbal IQ of 84% (range 55-102),performance IQ 89 % (63-116) and full scale 91% (73-108).Ictal EEG demonstrated the following findings: frontal-temporal(16%),bilateral temporal(27%),left temporal(16%),right temporal(21%),temporal-parietal(5%) and extra-temporal(16%). Interictal discharges correlated with ictal findings in 95% of cases. There was a 100% correlation between the findings on ictal scalp EEG and the post-implant grid. Findings on a Positron Emission Tomography correlated with ictal findings in 59% of cases. Conventional 1.5T-MRI was normal (non-lesional) in 42 % of the cases. However, 58% of cases had a positive MRI correlating with the previously defined IZ. 3T MRI performed in seven cases did not revealed any new findings. Fifteen patients (80%) underwent surgical resection as follows: anterior temporal lobectomy (58.3%), frontal corticectomy (26.5%), temporal-parietal corticectomy (5%) and posterior temporal corticectomy (5%). Pathological examination revealed: subpial gliosis (16%), hippocampal sclerosis (11%), polymicrogyria (5%), and neuronal loss (5%). Most cases (32%) did not demonstrate any abnormality. Seizure outcome revealed that 37% of cases remain seizure-free at six months post-surgery. Conclusions: Interim data analysis of this ongoing research study reveals that 3T BMRI findings did not show a significant difference when compared with a conventional 1.5T BMRI.