Diffusion tensor imaging in patients with epilepsy and malformations of cortical development

Abstract

Malformations of cortical development (MCD) are a common cause of epilepsy. Studies of structural MRIs and PET data in patients with MCD have found widespread changes outside the visually identified lesions. The aim of this study was to investigate diffusion changes interictally in patients with MCD and to test the hypothesis that MCD would be associated with widespread abnormalities of diffusion. We used diffusion tensor imaging (DTI) and statistical parametric mapping (SPM) to compare objectively tissue organization in 22 patients with partial seizures and MCD, with 30 control subjects. Whole-brain DTI was acquired using echo planar imaging. Rotationally invariant anisotropy and diffusivity maps were calculated and, after normalization to Talairach space, each patient was compared with the group of control subjects using SPM. Areas of reduced anisotropy were found in 17 patients and areas of increased diffusivity in 10. Two patients had areas of increased anisotropy. There were no patients with reduced diffusivity. Areas of increased diffusivity were in general more extensive than areas of reduced anisotropy. Changes in tissue beyond the MCD, that appeared normal on conventional MRI, were found in six patients for anisotropy and nine patients for diffusivity. Both measurements showed widespread changes in tissue beyond the MCD, i.e. adding information to conventional MRI. Increased or abnormally located grey matter or pathological white matter with abnormal myelination or ectopic neurones could cause reduced anisotropy. Increased diffusivity could be caused by a defect of neurogenesis or cell loss resulting in increased extracellular space. The widespread nature of abnormalities should be considered if surgical treatment is contemplated.

White matter hemisphere asymmetries in healthy subjects and in schizophrenia: a diffusion tensor MRI study

“…Most previous voxel-based DTI reports (Barnea-Goraly et al, 2003;Eriksson et al, 2001;Foong et al, 2002;Rugg-Gunn et al, 2001) have used a method similar to the one used for the voxel-based analysis of the structural scans called "voxel based morphometry".…”

“…In the analysis of gray matter, each gyrus and sulcus can be mapped to the corresponding template structure based only on the signal intensity obtained from T1-or T2-weighted images. However, structural MR images, which have been generally used for previous voxel-based studies of fractional anisotropy (Barnea-Goraly et al, 2003;Burns et al, 2003;Eriksson et al, 2001;Foong et al, 2002;Rugg-Gunn et al, 2001), do not include information essential for finding anatomical correspondence of the white matter structures (namely, fiber tract's orientation and organization) and thus might not be appropriate for finding precise anatomical correspondence in DT-MRI. This is why we used a more complex registration approach that utilizes multiple channel tensor information to match anatomical correspondence between subjects and between hemispheres instead of using fractional anisotropy or T2-weighted images, even for the analysis of fractional anisotropy.…”

Schizencephaly: as seen with MR tractography

“…Prior studies have shown reduced white matter in cerebral hemispheres, often with reduced diffusion (4,11,12). Lim et al presented a case with bilateral schizencephaly with radiating gray matter signal extending from the ventricle to the cortex; DTI was also used in that report (10).…”

Spectroscopy Evidence of Diffuse Brain Abnormalities in Patients with Epileptogenic Foci

“…Abnormal diffusion anisotropy has also been found beyond the visualized limits of MCD. 13 The fact that Leite and her colleagues found abnormal MR spectroscopy profiles even in the contralateral hemisphere is important but not surprising. The most important observation from their study is that one needs to be very cautious when using the contralateral brain as an internal control in patients with focal epilepsy.…”