Abstracts

On T1-weighted MRI, Taylor[rsquo]s focal cortical dysplasia (FCD) is characterized by a combination of increased cortical thickness, hyperintense signal within the dysplastic lesion relative to normal cortex and blurred transition between grey and white matter (GM/WM). The visual identification of these abnormal characteristics is difficult and it is unclear to which degree these features occur among different FCD lesions. Our purpose was to investigate the pattern of occurrence of abnormal MRI characteristics in FCD using a set of computational models. We studied 32 patients with known FCD lesions and 39 sex- and age-matched healthy control subjects. A set of voxel-wise operators were applied to high-resolution 3-D T1-weighted MRI for each subject using our previous methods (Antel et al., 2002), creating maps of cortical thickness, a relative intensity operator (designed to emphasize areas with hyperintense signal) and gradient magnitude (modeling the GM/WM transition). FCD lesions were segmented manually on the MRI by an expert observer. For each patient, we computed the mean thickness and relative intensity in the GM component of the FCD lesion. The gradient was computed along the edges of the lesion at the GM/WM interface. For the controls, the computation of each feature was performed in brain areas corresponding to the distribution of FCD lesions. In controls, mean, inter-subject standard deviation (SD) and ranges were calculated for each feature. Values were also calculated in FCD patients, and a given feature was considered abnormal if its value fell outside the range mean[plusmn]2SD. For each feature, mean, standard deviation and ranges are presented in the Table. In healthy controls, inter-subject variation was low for all three features (cortical thickness: 13%; relative intensity: 2%; gradient: 5%), indicating the high reliability of our measurements. Twenty-seven (84%) patients exhibited an increased cortical thickness, 27 (84%) an abnormal relative intensity and 30 (94%) a blurring of the GM/WM interface. All three features were abnormal in 22 (69%) patients, 8 (25%) had two abnormal features, and 2 (6%) had only one.[table1] The majority of FCD lesions are characterized by increased cortical thickness, a hyperintense signal and a blurring of the GM/WM transition. However, there is considerable variability in the pattern of these abnormalities across patients, some FCD lesions being characterized only by one or two of these features. FCD lesion profiling may assist the development of strategies for their visual and automatic detection on MRI.
Reference
Antel SB et al., Neuroimage 2002; 17: 1755-60. (Supported by Epilepsy Canada
Canadian Institutes for Health Research (CIHR) grant #203707
The Scottish Rite Charitable Foundation Canada.)