Abstracts

Rationale: Hippocampal sclerosis is the most common underlying pathology in drug resistant temporal lobe epilepsy. Identifying in vivo markers for hippocampal sclerosis is important in determining surgically amenable regions to reduce seizure frequency. Studies using MRI have shown that detection of hippocampal changes, associated with temporal lobe epilepsy, can be reliably detected using volumetric techniques. In addition, increases in hippocampal T2 signal have proven to be useful in identifying these hippocampal changes. Fluid-attenuated inversion-recovery (FLAIR) has been the favored method to view hippocampal intensity changes due to its ability to suppress adjacent cerebral spinal fluid, allowing for a more obvious detection of abnormalities. Since rating T2 signal intensity differences can be subject to rater bias, quantifying the T2 signal may prove important in determining differences in hippocampal signal intensity. In addition, relating the FLAIR signal intensity of the hippocampus to the structural volume changes, may aid in understanding the sensitivity of each technique in determining in vivo hippocampal abnormalities. In the present study we quantified FLAIR intensity differences in the hippocampus and compared these to differences to hippocampal volume in patients with temporal lobe epilepsy. Methods: Twenty five individuals with unilateral temporal lobe epilepsy (13 right and 12 left) as determined by long term video-EEG monitoring were included in this study. T1 weighted 3-D SPGR along with routine T2 weighted FLAIR MRI pulse sequences were acquired in all subjects. Hippocampal volumes were derived by manually tracing consecutive T1 coronal slices of the hippocampus. T1 images were coregistered to the FLAIR sequence, and the traced volumes were used as masks that were applied to the FLAIR images to extract average signal intensities for each hippocampus using statistical parametric mapping (SPM2). Finally, correlations were run to examine the relationship between the difference in right and left hippocampal volumes and the difference in right and left FLAIR signal intensities. Results: Of the 25 patients, 9 were found to have left hippocampal atrophy and 10 had right hippocampal atrophy over the corresponding predetermined region of onset. In addition, 4 participants had normal hippocampal volume and 2 had bilateral hippocampal atrophy. Correlations showed a significant relationship between hippocampal volume and FLAIR intensity differences (R=0.562, p=0.003). Conclusions: The results of this study show that T2 intensity values can be quantified from routine T2 FLAIR sequences. Furthermore, increases in FLAIR intensity values are directly related to decreases in hippocampal volume. These findings support the use of not only hippocampal volume but also quantitative FLAIR intensities for in vivo detection of hippocampal abnormalities to improve seizure lateralization and surgical outcome.