Abstracts

Diffusion tensor imaging (DTI) provides information about the magnitude (diffusivity) and directionality (anisotropy) of water diffusion. The purpose of the study was to explore the characteristics of pathology proven cortical dysplasia (CD) using DTI measures, and to assess alterations in white matter tracts and subcortical connectivity. DTI was performed in 6 patients with pathologically-proven cortical dysplasia. All patients underwent surgery for intractable epilepsy, 5 after invasive grid evaluation. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC, in x 10 ^-5 mm²/s) were determined within the dysplastic lesion using a region of interest (ROI) approach by outlining the entire visible lesion in the FCD group and a representative ROI within the area of abnormal gyration resected in patients with more widespread abnormalities. Comparison was made to contralateral gray matter (cGM) and white matter (cWM) measurements. The FA maps were visually inspected in all patients and tractography (using the DTI task card) was performed in three to assess connectivity of the dysplastic cortex. Three patients had cortical thickening on T1-weighted MRI and signal increase on FLAIR (two occipital, one frontal). Pathology revealed Type IIB (balloon cell) CD. The ADC within the dysplastic lesion (iGM) was marginally higher compared to cGM (CD 89.7[underline]+[/underline]7.1, cGM 83.9[underline]+[/underline]7.0, P[lt]0.07). Mean FA in the CD (iGM) was comparable to cGM values. Three patients had heterotopic gray matter and gyration abnormalities (two perisylvian, one occipital and basal temporal) with Type IA CD (architectural abnormalities) on pathology. The GM and WM values were comparable in representative homotopic areas.
Analysis of FA maps revealed reduced arborization and thinning of the fiber bundles between the subcortical WM and the dysplastic cortex in 2 of the 3 patients with Type IIB CD. Reduced subcortical connectivity was confirmed on tractography. One patient with a small mesial frontal FCD showed a normal pattern on the FA map. Of the three patients with CD and widespread gyration abnormalities, abnormal pattern of subcortical connectivity with a reduction of fibers was observed, and in one patient displacement of adjacent tracts was seen and better visualized using tractography. Diffusivity measures and visualization of tracts provide complementary information on white matter changes accompanying CD and may assist to localize and fully delineate CD. Careful correlation with cortical stimulation and other measures of function will allow to assess the functional significance of various dysplastic lesions and may help to design resective strategies. (Supported by the CCF Investigator Development Award (BD).)