Abstracts

Rationale: Hippocampal sclerosis (HS) is the most common pathology of non-lesional temporal lobe epilepsy (NLTLE). Most of them can be detected on a high resolution structural MRI. However, a significant number of patients with NLTLE with EEG and clinically well-lateralized temporal lobe seizures have no evidence of HS on high resolution structural MRI. Diffusion tensor imaging (DTI) can provide information about white matter fiber orientation and integrity. Proton MRS allows detecting early metabolic alterations in the brain even before structural changes. In this study we investigate whether DTI and MRS can provide extra information about hippocampal formation (HF) integrity in structural negative NLTLE. Methods: We retrospectively analyzed 10 patients with EEG evidence of well-lateralized temporal lobe epilepsy. All patients had high resolution structural MRI, DTI, and MRS. All MRIs were performed in 3T MR Scanner. The standard high resolution structural MRIs were reviewed by a neuroradiologist who was blind to the lateralization of the seizures. Mean diffusion (MD) and fractional anisotropy (FA)were measured from region of interest(ROIs) on anterior HF bilaterally. MRS was performed with single voxel (15mm x 15 mm x 15mm) sampling from anterior HF bilaterally. The MD, FA and NAA/Cr ratio were compared between ipsilateral and contralateral to the epileptogenic zone as determined on the basis of interictal and ictal scalp EEG recordings. Paired samples test was performed in this study. This study was approved by the University of Illinois College of Medicine at Peoria IRB. Results: There is significant difference in all MD, FA, and NAA/Cr ratio between ipsilateral and contralateral side of HF. In the ipsilateral side to the epileptogenic zone, MD significantly increased (10.47 /- 1.08 x 10-4 mm2/s vs 9.267 /- 0.57 x 10-4 mm2/s ) ( p = 0.012); FA significantly decreased (0.124 /-0.019 vs 0.15 /- 0.015) ( p = 0.03); and NAA/Cr ratio significant decreased (1.28 /- 0.12 vs 1.45 /- 0.13 ) ( p = 0.014). Conclusions: The results suggest that DTI and MRS could provide complementary information to help identify the HS on structural MRI negative NLTLE. They also suggest that both gray matter and white matter are involved in HS even before it can be detected by high resolution structural MRI.