Diffusion tensor imaging in polymicrogyria: A report of three cases

Introduction: Polymicrogyria (PMG), a neuronal migration disorder, commonly manifests as a seizure disorder. The aim of this study was to look for the abnormalities in the underlying white matter using diffusion tensor imaging (DTI) that appeared normal on conventional magnetic resonance imaging (MRI) in patients with PMG. Methods: DTI was performed in three patients with PMG and eight age- and sex-matched healthy controls. Fractional anisotropy (FA) and mean diffusivity (MD) values were calculated for the cortex and adjoining subcortical white matter in both controls and patients. Results: We observed a significantly decreased mean FA value with no significant change in the MD value in subcortical white matter underlying polymicrogyric cortex (FA=0.23±0.04, MD=1.0±0.05 × 10^-3 mm²/s) as compared to both contralateral (FA=0.32±0.04, MD=1.0±0.05×10^-3mm²/s) and normal control (FA=0.32±0.04, MD=1.0±0.06 10^-3 mm²/s) white matter. Significantly increased MD and decreased FA values were also observed in the polymicrogyric cortex (FA=0.08±0.01, MD=1.2±0.10×10^-3 mm²/s) as compared to normal contralateral (FA=0.12±0.04, MD=1.1±0.09×10^-3 mm²/s) and normal control (FA=0.12±0.01, MD=1.1±0.09×10^-3 mm²/s) cortex. Conclusion: Significantly decreased FA values with no change in MD values in the subcortical white matter subjacent to polymicrogyric cortex reflect microstructural changes in the white matter probably due to the presence of ectopic neurons.