Subcortical alterations in tissue microstructure adjacent to focal cortical dysplasia: Detection at diffusion-tensor MR imaging by using magnetoencephalographic dipole cluster localization

Purpose: To determine whether changes at diffusion-tensor magnetic resonance (MR) imaging were present in children with intractable epilepsy and focal cortical dysplasia (FCD) in (a) subcortical white matter subjacent to MR imaging-visible areas of FCD, (b) subcortical white matter beyond the MR imaging-visible abnormality but subjacent to a magnetoencephalographic (MEG) dipole cluster, and (c) deep white matter tracts. Materials and Methods: The study protocol had institutional research ethics board approval, and written informed consent was obtained. Fifteen children with FCD and intractable epilepsy (mean age, 11.6 years; range, 3.6-18.3 years) underwent diffusion-tensor MR imaging and MEG. Regions of interest were placed in (a) the subcortical white matter subjacent to the MR imaging-visible abnormality, as well as the contralateral side; (b) the subcortical white matter beyond the MR imaging-visible abnormality but subjacent to a MEG dipole cluster, as well as the contralateral side; and (c) deep white matter tracts projecting to or from the MR imaging-visible FCD, as well as the contralateral side. Fractional anisotropy (FA), mean diffusivity, and eigenvalues (λ1, λ2, λ3) were evaluated. Results: Eleven of 15 children had MEG dipole clusters, and four children had MEG scatter. There were significant differences in FA, mean diffusivity, λ₂, and λ₃ of the subcortical white matter subjacent to the MR imaging-visible FCD (P < .001 for all), as well as that beyond the MR imaging-visible FCD but subjacent to a MEG dipole cluster (P = .001, P < .036, P = .001, and P = .002, respectively), compared with the contralateral side. There were also significant differences in FA (P < .001), mean diffusivity (P = .008), λ2 (P < .001), and λ₃ (P = .001) of the deep white matter tracts projecting to or from the MR imaging-visible FCD compared with the contralateral side. Conclusion: With use of MEG dipole clusters to localize the epileptogenic zone, diffusion-tensor imaging can help identify alterations in tissue microstructure beyond the MR imaging-visible FCD.