FOCAL CORTICAL DYSPLASIA AND HEMIMEGALENCEPHALY - HISTOLOGICAL AND NEUROIMAGING CORRELATIONS

Background. The classification of cerebral cortical dysplasia is diffi cult and there are histological similarities between focal cortical dy splasia (FCD) and hemimegalencephaly, Objectives. To correlate the MR features and histological data of cortical dysplasias, Materials and m ethods. The MR appearances of 17 brains were examined. According to th e signal intensity within the pathological area on T2-weighted (T2-W) sequences we selected two groups. Results. Group 1 comprised ten patie nts with high signal in the dysplastic area on T2-W images. This group included five hemimegalencephalies, three frontal quadramegalencephal ies, and one gyral dysplasia, The pathological hemisphere was reduced in size in one case. The cortex was thickened in all cases on T1-weigh ted (T1-W) images. There was loss of delineation between white matter (WM) and grey matter (GM) in all cases on both T1-W and T2-W sequences . The differential diagnosis with tumour, neoplastic-like malformation or polymicrogyria was questionable. Group 2 comprised seven patients presenting without increased signal within the dysplastic area on T2-W images. WM and GM were of similar signal intensity in six cases, and delineation between white and grey matter was absent in all cases. The re were mild abnormalities on T1-W sequences in all cases, The dysplas ias were limited to a lobe in five cases and a gyrus in two cases. In all cases, depiction of the malformation was a greater diagnostic prob lem than the differential diagnosis. Conclusions. A constant MR sign i n our series was the loss of delineation between WM and GM in the dysp lastic area. This correlated well with the observed histological disor ganisation. Markedly high signal within the dysplastic area seems to b e related to myelin abnormalities rather than glial cell abnormalities .