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Cortical dysplasia (CD) is the most epileptogenic structural lesion associated with epilepsy and patients with intractable seizures caused by this condition are good surgical candidates. MRI plays an important role in detecting the abnormalities of CD. We clarified the MRI characteristics of CD by comparing imaging and histological findings in 20 patients with intractable seizures who underwent surgical resection. There were 12 males and eight females, mean age at operation was 15 years. MRI was performed at 1.5 tesla; T1-weighted, T2- and proton density-weighted spin-echo and fluid-attenuated inversion-recovery (FLAIR) images were obtained. The lesions were in the frontal lobe in nine cases, temporal in two, occipital in another two, insular in one and multilobar in six. Blurring of the grey/white matter junction was seen in all patients, and T2 prolongation in white matter and/or at the grey/white matter junction in 19. Abnormal signal intensity was more frequent in the white matter or at the grey/white matter junction than in the grey matter. FLAIR images made this abnormal high signal easier to appreciate, and we thought them very useful in this context. In areas of T2 prolongation, we saw dysplastic neurones and/or balloon cells, dysmyelination, and ectopic neuronal clustering histologically; glial proliferation played an important role in prolonging T2.

There exist various morphological and biochemical changes closely associated with electrophysiological phenomena which cause epileptic seizures in the brains of epilepsy patients. Recent developments in investigation methods, not only electrophysiological(EEG and MEG), but also neuroimaging involving morphological imaging(CT and conventional MRI) and functional imaging(SPECT, PET, functional MRI and MRS) is able to demonstrate these changes. SPECT and PET can particularly clarify the changes of cerebral blood flow and glucose metabolism between interictal and ictal periods. In our experience of 423 patients who underwent epilepsy surgery for intractable seizures, these interventions provide important information to identify the epileptogenic foci. However, in practice, discordance in the results of these presurgical evaluations is recognized, and invasive intracranial recordings are needed in such cases. These problems in diagnosis were shown especially in patients with mesial temporal sclerosis and focal cortical dysplasia. To detect an epileptogenic focus more clearly, a combination of morphological and functional findings, new functional imaging such as neurotransmitter receptor imaging, EEG-triggered or neuropharmacological functional MRI, as well as, statistical parametric analysis may be needed.