Hippocampal and Thalamic Diffusion Abnormalities in Children with Temporal Lobe Epilepsy

Previous studies using diffusion MRI in patients with temporal lobe epilepsy have shown abnormal water diffusion in the hippocampus. Because thalamus and lentiform nuclei are considered important for the regulation of cortical excitability and seizure propagation, we analyzed diffusion tensor imaging (DTI) abnormalities in these subcortical structures and in hippocampus of children with partial epilepsy with and without secondary generalization.Fourteen children with partial epilepsy involving the temporal lobe underwent MRI including a DTI sequence. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were obtained in the hippocampus, thalamus, and lentiform nucleus, and compared with DTI data of 14 control children with no epilepsy, as well as glucose positron emission tomography (PET) findings.Decreased FA (p < 0.001) and increased ADC (p = 0.003) values were found in the hippocampi ipsilateral to the seizure focus. Significant FA decreases (p = 0.002) also were seen in the contralateral hippocampi, despite unilateral seizure onset and excellent surgical outcome in patients who underwent surgery. ADC values showed a trend for increase in the thalami ipsilateral to the epileptic focus in the seven children with secondarily generalized seizures (p = 0.09). No group differences of ADC or FA were found in the lentiform nuclei. The DTI variables did not correlate with regional glucose metabolism in any of the structures analyzed.Increased ADC values in hippocampus can assist in lateralizing the seizure focus, but decreased FA in the contralateral hippocampus suggests that it too may be dysfunctional despite unilateral seizure onset. Less-robust thalamic abnormalities of water diffusion in patients with secondarily generalized seizures suggest secondary involvement of the thalamus, perhaps due to recruitment of this structure into the epileptic network; however, this must be confirmed in a larger population. DTI appears to be a sensitive method for detection abnormalities in children with partial epilepsy, even in structures without apparent changes on conventional MRI.