Abstracts

Rationale: Functional MRI (fMRI) has been increasing used to study the impact of temporal lobe epilepsy (TLE) over the past decade. Effect of seizures in medically refractory TLE causing reorganization of memory circuits, prior to anterior temporal lobectomy (ATL), has been observed in some previous fMRI studies. However, demonstration of potential reorganization after ATL has been rarely studied. Methods: Nineteen patients with medically intractable TLE and 15 healthy controls were enrolled in this study. Ten patients underwent left ATL and 9 underwent right ATL. Group analyses of a novelty scene-encoding paradigm comparing areas of blood oxygen-level-dependent (BOLD) signal activation pre- and post-ATL were performed and separately analyzed between left (LTLE) and right TLE (RTLE) patients . Among these 19 patients, a time period of performing post-operative fMRI varied from 2 to 26 months after the surgery, with a mean period of 12 months. Effect of time after the surgery on memory circuits reorganization was further assessed by comparison in each group between the patients who performed the post-ATL fMRI study at 6 months or less and after 6 months. Results: Patient's age was between 20 and 63 years (mean 40.4 ± 13.0) and age onset of epilepsy was between 2 and 55 years (mean 21.9 ± 13.5). Fifteen, three, and one patient achieved Engel Class I, II and III surgical outcome, respectively. Pathology revealed hippocampal sclerosis in 12, gliosis in 5, and benign tumors in 2 patients. Pre-operative fMRI study showed smaller hippocampal and parahippocampal activation ipsilateral to the side of epileptogenic focus in both LTLE and RTLE patients. Also, contralateral extra-temporal either frontal or parietal lobe signal activation was observed in both groups, but statistically significant on the RTLE group (p = 0.04). In comparison to pre-operative study, shifting areas of activation at the post-operative study were disclosed over temporal region, with statistically significance in post-right ATL (p = 0.01). This reorganization was accentuated appearing to be more robust and wider activation over time after the surgery (greater over 6 months), once again statistically significant in post-right ATL group. Conclusions: Disturbance of normal memory circuits prior to the surgery in TLE demonstrating extratemporal recruitment was observed. Reorganization after ATL localized to the temporal area was seen in both LTLE and RTLE patients. Post-operative greater activation over time particularly at after 6 months was noted. However, statistically significant areas of fMRI activation were appreciated in RTLE group.