Abstracts

Rationale: Epilepsy affects approximately 1% of the population and is drug resistant (DRE) in 30% of the patients. Childhood-onset DRE can be associated with long-term effects on a child’s development, behavior, and cognition. Different authors demonstrated structural MRI changes that gets more pronounced in adults with longer duration of epilepsy. The clearest evidence of progressive MRI changes in DRE is progressive and irreversible scarring of the medial temporal lobes in patients with seizure onset outside of the temporal lobes, detected on visual examination of MRI scans and referred to as mesial temporal sclerosis (MTS). MTS is typically seen in adults and is often associated with memory impairments. Memory deficits can also be seen in children with long duration of DRE in the absence of MTS suggesting potential secondary hippocampal injury. The purpose of this study is to utilize computational MRI analysis to evaluate longitudinal volumetric changes in the hippocampus in pediatric patients with DRE, as well as to examine whether the extent of these changes is dependent on epilepsy lateralization

Methods: We studied pediatric patients with DRE evaluated for epilepsy surgery. We included patients who underwent more than one MRI scan during their presurgical evaluation and have no MTS on visual inspection of the MRI. We excluded patients with multilobar or large structural lesions and patients with seizures arising from the mesial temporal structures. All scanning was performed on a single 3-T Philips Achieve whole body scanner. Whole-brain volumetric segmentation and cortical surface reconstruction was performed, and total volumes of the hippocampi were measured through an open-source software FreeSurfer 7.1 (https://surfer.nmr.mgh.harvard.edu). Hippocampal asymmetry index (AI) was calculated as volumes of ipsilateral hippocampus-contralateral hippocampus/sum of both hippocampi. A linear regression mode was carried out to determine changes in hippocampal volume over time

Results: 40 patients with intractable focal epilepsy were included. History of generalized tonic-clonic (GTC) seizures was present in 23 patients. Seizure onset was localized to the right (n=21) and left hemisphere (n=19). Age at seizure onset (mean ± SD 7.3 ± 4.3 years), at first MRI 11.1 ± 4.1 years and 14.6 ± 4.2 at their last MRI. Epilepsy localization was frontal (n=18), centroparietal (n = 9), cingulate (n= 3), neocortical temporal (n=7) and occipital (n=3). Progressive hippocampal asymmetry is noted with asymmetric hippocampal atrophy ipsilateral to the seizure onset (Figure 1). Reduction in hippocampal volume is seen more prominent with left sided epilepsy and is correlated with the duration of epilepsy and history of GTC seizures (figure 2).

Conclusions: This study provides evidence of progressive hippocampal thinning in pediatric DRE with no evidence of radiologic MTS. These changes are correlated with the duration of epilepsy, history of GTCs and are more prominent ipsilateral to the seizure onset

Funding: Please list any funding that was received in support of this abstract.: This study was funded through Pediatric KPRI grant and NSF-EPSCoR # 1632891.