Abstracts

Rationale: In patients with temporal lobe epilepsy (TLE) without any evidence of hippocampal sclerosis on MRI (hippocampal sclerosis and/or increased T2 signal), it has been previously shown that hippocampal internal architecture asymmetry (HIA) is a predictor of the site of seizure onset with high sensitivity and specificity. Further, patients with conventional evidence of hippocampal sclerosis have a poorer prognosis and are more likely to be medication resistant. The purpose of this study was to determine if the loss of HIA clarity is predictive of drug resistant TLE (drTLE) in comparison to patients with well-controlled TLE (wcTLE). Methods: Included in this study were 5 patients with medically wcTLE, defined as seizure free for greater than one year at most recent clinic follow up without the need for surgery (mean age 46.8 ± 11.9 yrs, 4 females) and 30 patients with drTLE, defined as not seizure free at most recent clinic follow up or prior to surgery (mean age 38.7 ± 13.7 yrs, 20 females). Diagnosis of TLE in all patients was determined by ictal video EEG evidence of unilateral temporal lobe epilepsy (18 right TLE, 17 left TLE). T2 weighted, high resolution (.25mm x .25mm) coronal slices were analyzed with a novel quantitative technique that calculates the conspicuity of the hypointense band of white matter that defines HIA. From these measurements, a conspicuity index (CI) was calculated, which is a function of the number of dark pixels and the contrast-to-noise ratio between those pixels and the adjacent hippocampal grey matter in the CA4 region. The difference in the CI between the right and left hippocampi in each patient was used as the measure of HIA asymmetry (0=symmetric). Using a one-tailed t-test, we tested the hypothesis that there is a lower degree of HIA asymmetry in the wcTLE patients than the drTLE patients, meaning that the wcTLE patients were hypothesized to have more symmetric appearing hippocampi. Results: The mean HIA asymmetry in the wcTLE group was 0.26 (SD 0.189, SE 0.084), and the mean HIA asymmetry in the drTLE group was 0.49 (SD 0.415, SE 0.075). A one-tailed student's t-test showed a significant difference between the groups (p=0.03), confirming the hypothesis that there was a lower degree of asymmetry in the wcTLE group. Conclusions: The findings suggest that increased HIA asymmetry in TLE patients is associated with drTLE. In addition, a novel quantitative technique has been introduced to calculate a numerical value which quantitatively represents HIA asymmetry. These imaging findings could potentially aid in predicting likelihood of drug resistance in TLE in the future.