Measures of hippocampal volumes, diffusion and 1H MRS metabolic abnormalities in temporal lobe epilepsy provide partially complementary information

We assessed whether interictal measures of hippocampal volume, hippocampal diffusion and metabolic abnormalities yield correlated or complementary information about hippocampal pathology in patients with temporal lobe epilepsy (TLE). Volumes, apparent diffusion coefficients (ADC) and ratios of N-acetyl-aspartate (NAA) to Creatine/Phosphocreatine (Cr) and Choline (Cho) were measured from each hippocampus during one magnetic resonance imaging (MRI) session in patients with TLE. Structural MRI showed unilateral hippocampal sclerosis (HS) in 13 patients and was normal in the remaining nine patients. Pearson's correlation (two-tailed) between ADC values and NAA/(Cr+Cho) ratios was significant (P=0.04, r=-0.45) for the hippocampus ipsilateral to the epileptogenic zone as determined on the basis of interictal and ictal scalp EEG recordings. This finding was driven by a very high correlation between the two measures in the presence of HS (P<0.001, r=-0.96). Furthermore, ipsilateral ADC values but not NAA/(Cr+Cho) ratios were correlated with disease duration (P=0.001, r=0.67). Hippocampal volumes did not correlate with either ADC values, NAA/(Cr+Cho) ratios or disease duration. These data suggest that hippocampal volumes, NAA/(Cr+Cho) ratios and ADC values capture partially complementary aspects of hippocampal pathology.