Bilateral diffusion tensor abnormalities of temporal lobe and cingulate gyrus white matter in children with temporal lobe epilepsy.

PURPOSE: Bilateral diffusion tensor imaging (DTI) abnormalities have been reported in the white matter associated to the hippocampus in adults with mesial temporal lobe epilepsy (TLE). In children with a shorter duration of epilepsy, such changes may not have yet emerged. The aim of this study was to investigate interictal changes in the temporal lobe white matter (TLWM) and cingulate gyrus white matter (CGWM) of children with TLE using DTI. METHODS: DTI was performed in eight children with TLE and 10 healthy, age-matched controls. Fractional anisotropy (FA), trace, parallel (lambda(||)) and perpendicular (lambda( perpendicular)) diffusivity were calculated for a volume of interest in the TLWM and CGWM on the seizure focus side and the contralateral side. Data were compared for differences between sides for patients and between patients and controls. RESULTS: There was no significant difference in FA, trace, lambda(||) and lambda( perpendicular) between TLWM and CGWM on the seizure focus side versus the contralateral side in TLE patients. Increased diffusivity, lambda(||) and lambda( perpendicular) within the TLWM and CGWM were found in TLE patients compared to controls, but no significant difference in FA was seen. CONCLUSIONS: Bilaterally increased diffusivity, lambda(||) and lambda( perpendicular) in the white matter in children with TLE may be related to seizure induced functional or structural changes. The preserved FA in our pediatric cohort is in contrast to the reduced FA in the white matter of adults with TLE and may relate to differences in the duration of epilepsy or in the vulnerability of white matter to seizures.

Preserved structural integrity of white matter adjacent to low-grade tumors.

BACKGROUND AND PURPOSE: Brain tumors may dislocate, infiltrate, or disrupt the adjacent fiber tracts. We examined (1) microstructural changes of white matter (WM) adjacent to supratentorial low grade tumors in children and (2) WM tracts of the affected hemisphere using diffusion tensor imaging (DTI). We hypothesized that the structural integrity of the adjacent WM tracts would be preserved in these slow-growing tumors. MATERIALS AND METHODS: DTI was performed in 11 children with low grade tumors diagnosed by magnetic resonance imaging (MRI). Regions of interest were placed in the tumor, in WM adjacent to tumor, and on the normal contralateral side. Fractional anisotropy (FA), trace, and eigenvalues were measured. Color-coded maps and tractography were used to grade the WM tracts: Grade one was normal tract size and color hue; grade two was reduced tract size but preserved color hue; and grade three was loss of color hue or failure to track on tractography. Grades one and two were subcategorized as "a" or "b," depending on the absence or presence of tract displacement. RESULTS: There were no significant differences in FA, trace, and eigenvalues between WM adjacent to tumor and the contralateral side. One patient had grade 1a changes, six grade 1b, and four grade 2b. CONCLUSION: We found preserved microstructural integrity of WM adjacent to low grade tumors in children. Color vector maps and tractography demonstrated displacement of the WM tracts in all but one patient. Our findings could be useful for neurosurgical planning to minimize injury to the WM tracts and improve preoperative risk analysis.

Evaluation of subcortical white matter and deep white matter tracts in malformations of cortical development.

AIMS: Abnormal cortical development will lead to abnormal axons in white matter. The purpose was to investigate (1) the microstructural changes in subcortical white matter adjacent to malformations of cortical development (MCD) and (2) the deep white matter tracts using diffusion tensor imaging (DTI). METHODS: Thirteen children with a variety of MCD were recruited. The fractional anisotropy (FA), trace, and eigenvalues (lambdamajor, lambdamedium, lambdaminor) of subcortical white matter of MCD were compared with contralateral normal side. The deep white matter tracts were graded based on the size, color hues and displacement of the tracts as visualized on color vector maps and tractography; grade 1 was normal tract size and color hue, grade 2 was reduced tract size but preserved color hue and grade 3 was loss of color hue or failure of tracking on tractography. RESULTS: The subcortical white matter adjacent to abnormal cortex demonstrated reduced FA (p < 0.05) and tendency to increase trace (p = 0.06). There was a significant elevation in lambdamedium and lambdaminor (p < 0.05), but no significant change in lambdamajor (p > 0.05). Twelve cases demonstrated alteration in white matter tracts. Seven cases of focal cortical dysplasia and two cases of transmantle MCD demonstrated grade 3 pattern of white matter tract. CONCLUSION: Reduced FA is a sensitive but nonspecific marker of alteration in microstructure of white matter. The elevated lambdamedium and lambdaminor may reflect a dominant effect of abnormal myelin. Alteration in white matter tracts was observed in most cases of MCD.