Abstracts

Rationale: Mesial temporal sclerosis (MTS) in patients with epilepsy is known to be correlated with reduced hippocampal volume. While this association exists, the cause is not fully understood. The number of years that an individual has had epilepsy is thought to relate to hippocampal volume even in patients without MTS. In this study, we sought to determine if duration of time since seizure diagnosis could predict hippocampal volume in epilepsy patients with and without MTS. Methods: 37 adults (24F/13M; mean sd age = 38.24 10.59) with intractable epilepsy who were surgical candidates monitored at the Barrow Neurological Institute (BNI) Epilepsy Monitoring Unit (EMU) were included in this dataset. These individuals all had 1.5 or 3T T1-weighted magnetic resonance imaging (MRI) scans. Regional cortical thickness values and structural volumes were computed for each subject using the FreeSurfer software package. Onset side of seizures was determined for the each participant based on EEG recordings, MRI scans, and seismology based on consensus at EMU conference meetings. 14 had right and 21 had left sided seizure onset. Of those with right sided onset, 9 had right medial temporal sclerosis (MTS) and 12 had left sided MTS. Using the left and right sided groups, after controlling for age and volume of the contralateral hippocampus, multiple regression was used to determine if the number of years of having a seizure could predict hippocampal volume on the ipsilateral side as seizure onset. Results: Number of years of having a seizure disorder predicted left hippocampal volume after controlling for age and the volume of the right hippocampus, (R2 change=0.30, p=0.007). It was not significant in predicting right sided hippocampal volume. Using only the participants with MTS, left sided hippocampal volume again was predicted by years of having a seizure (R2 change=0.38, p=0.05), but right sided volume was not after controlling for age and contralateral hippocampal volume. This did not remain statistically significant when using only the participants who did not have MTS. Conclusions: Hippocampal volume is predicted by number of years of having a seizure in a mixed group of epilepsy patients both with and without MTS. A larger sample size would assist with determining whether this relationship remains when using only epilepsy patients without MTS. Small sample size may have also been a factor in explaining why left but not right hippocampal volume was predicted by seizure duration.