Epileptogenic networks: cerebral dysplasias and cerebral ectopias - Functional neuroimaging

There are three areas in which functional imaging may be applied to malform ations of cortical development (MCD) that give rise to epilepsy: the locali zation of epileptic activity; the identification of areas of functional abn ormality; the mapping of normal cerebral functions, and how these may be di splaced. Single photon emission computerized tomography (SPECT) commonly shows Inter ictal hypoperfusion and iota[ hyperperfusion. Positron emission tomography (PET), using F-18-fluorodeoxyglucose, often shows glucose metabolism in ect opic grey matter and hypometabolism in MCD, compared with normal cortex. Co gnitive activation tasks, using PET or fMRI, have shown that malformed cort ex may participate in cerebral functions, but also widespread atypical cort ical organization. Cognitive activation tasks using fMRI are useful when pl anning surgical resections close to eloquent cortex. Binding of C-11-flumazenil to central benzodiazepine receptors (cBZR) is of ten abnormal in MCD, and in areas of cortex that appear normal on MRI, with increased and decreased binding. MR Spectroscopy also reveals abnormalities that are more extensive than the MRI visible lesion, implying more widespread structural and functional abn ormalities. The recording of EEG during fMRI has allowed the latter to be used to local ize cerebral areas involved in the generation of interictal epileptiform ac tivity. Electroencephalograph source localization and magneto-encephalograp hy may also prove to be useful in the localization of Interictal epileptifo rm activity, particularly when fMRI data are used to constrain the solution s.