Extratemporal White Matter Abnormalities in Mesial Temporal Lobe Epilepsy Demonstrated with Diffusion Tensor Imaging

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Abstract
Summary: Purpose: Recent studies have demonstrated bilat- eral white matter abnormalities in temporal lobe epilepsy (TLE) patients with unilateral mesial temporal sclerosis (MTS). The purpose of this project was to determine whether abnormali- ties of water diffusion are seen in extratemporal white matter of patients with TLE and pathologically confirmed MTS and to determine whether these findings are associated with worse surgical outcome. Methods: Eleven patients with TLE and unilateral MTS con- firmed in surgical specimens and 14 controls were studied by using cerebrospinal fluid-suppressed diffusion tensor imaging (DTI) and T2 relaxometry. Results: Hippocampal T2 signal for patients was significantly elevated both ipsilateral (p < 0.001) and contralateral (p = 0.006) to MTS. DTI demonstrated reduced fractional anisotropy of the genu of the corpus callosum (p = 0.003) and external capsule (p = 0.02) and elevated mean diffusivity of the genu (p = 0.005), splenium (p = 0.03), and external capsule (p < 0.001). For both the genu and external capsule, parallel diffu- sion of patients was not different from that of controls (genu, p = 0.81; external capsule, p = 0.45), whereas perpendicu- lar diffusion was elevated (genu, p = 0.001; external capsule, p < 0.001). With mean postsurgical follow-up of 18.5 months, eight of 11 patients were entirely seizure free and the remain- ing three had all experienced a worthwhile reduction in seizure frequency. Conclusions: Our findings suggest that although patients with TLE and MTS have extensive bilateral and extratemporal pathol- ogy, these findings may not be associated with a worse postsur- gical outcome. Key Words: Temporal lobe epilepsy—Mesial temporal sclerosis—Diffusion tensor imaging—Anisotropy— DTI.