Abstracts

Subcortical structures, especially thalamus, are considered important for the regulation of cortical excitability and seizure propagation in human epilepsy. Previous studies in temporal lobe epilepsy showed abnormalities of water diffusion in the hippocampus. The purpose of this study was to analyze diffusion tensor imaging (DTI) abnormalities in subcortical structures and hippocampus of children with partial epilepsy of temporal lobe origin with (N=7) and without (N=7) secondary generalization. Fourteen children with unilateral temporal lobe epilepsy underwent MRI including DTI and EEG monitoring. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were obtained in thalamus, lentiform nucleus, and hippocampus. In addition, 10 of the patients had glucose PET scans and nine patients had volumetric MR images performed. For these patients, glucose metabolism and volumes were also analyzed in these three structures. ADC and FA in the thalamus ipsilateral to the epileptic focus showed significantly higher values than on the contralateral side in patients with secondary generalized seizures (p=0.015 and 0.006, respectively; paired t-test), but not in those with partial seizures only (p=0.06 and p=0.26, respectively). Increased ADC and decreased FA values were observed in the hippocampus ipsilateral to the seizure focus when the entire group (N=14) was analyzed (p=0.03 and p=0.02, respectively). No significant side differences of ADC or FA were found in the lentiform nuclei. In glucose metabolism measurements, only thalamus showed lower glucose metabolism on the side of epileptic focus. No significant group asymmetries were found in volumetric measurements. These results demonstrate differential changes of ADC in the hippocampus and thalamus ipsilateral to the seizure focus of children with temporal lobe epilepsy. Increased ADC and decreased FA in hippocampus ipsilateral to the seizure focus have been described previously in adults with temporal lobe epilepsy. Increased thalamic ADC and FA ipsilateral to the focus in patients with secondary generalized seizures is a new finding suggesting secondary involvement of the thalamus, perhaps due to recruitment of this structure into the epileptic network, as shown in animal studies. DTI is a sensitive method to detect such remote abnormalities even in cases in which no structural changes are apparent on conventional MRI.