Abstracts

Rationale: Studies using operator-defined volumetric measurements and statistical parametric mapping demonstrate that morphological abnormalities in patients with refractory mesial temporal lobe epilepsy and hippocampal sclerosis extend beyond the mesial temporal structures. We investigated if similar abnormalities can be found in nonlesional temporal lobe epilepsy patients.Methods: We identified 18 adult patients who had undergone invasive evaluation for nonlesional pharmacoresistant epilepsy and were seizure free 6 months after surgery. All patients were judged to have normal brain MRI scans on review by a multidisciplinary patient management conference panel that included experienced neuroradiologists and epileptologists. MRIs of 18 healthy adult volunteers served as controls. We performed blinded manual measurements of hippocampal and temporal lobe volumes and grey-white matter segmentation of the temporal lobes on the coronal MPRAGE volume acquisition sequence. Electrophysiology data and histopathology slides were reviewed. Statistical analysis was performed using Bonferroni correction on paired and unpaired t-tests where applicable. Results: 13 patients had left temporal lobe epilepsy, 5 patients right temporal lobe epilepsy. 12 patients had mesial, 6 lateral temporal lobe epilepsy (based on invasive EEG recordings). On histopathology, 6 patients had a malformation of cortical development (type IA N=5, type IIa N=1). 3 patients had isolated hamartia. 9 patients had nonspecific gliosis. There were no differences in temporal lobe volumes, temporal lobe white and gray matter segments and hippocampal volumes between patients and controls, neither when analyzing the entire patient sample nor when looking at patient subgroups (left vs right and lateral vs mesial temporal lobe epilepsy). Side to side comparison revealed smaller temporal lobes ipsilateral to the epileptogenic zone in patients, whereas the mesial temporal structures were larger compared to the contralateral side. These findings persisted in the subgroups of patients with left temporal resections and in those with presumed mesial temporal epilepsy. All measured parameters were symmetric in the control group. Conclusions: Relative temporal lobe volume loss ipsilateral to the epileptogenic zone may indicate subtle structural brain abnormalities in patients with nonlesional temporal lobe epilepsy.