Stereoelectroencephalography in focal cortical dysplasia - A 3D approach to delineating the dysplastic cortex

Focal cortical dysplasia (FCD) is an increasingly recognized cause of intra ctable epilepsy, Surgical data suggest that the dysplastic cortex should be removed to obtain freedom from seizures, but the prognosis remains poor as FCD is difficult to delineate by imaging, We retrospectively analysed a se ries of 28 patients (aged 5-41 years, median 16.5 years) with FCD who had b een investigated by stereoelectroencephalography (SEEG) between 1964 and 19 95, Neurophysiological data were correlated with histological findings and surgical outcome, MRI was available for only seven patients, Severe partial epilepsy of early onset, pre-existing neurological deficit (68%) and cogni tive impairment were the main clinical features, FCD was distributed equall y between all lobes except for the temporal lobe, and was found predominant ly on the mesial aspect of the cerebral hemispheres, SEEG findings provided evidence of dysplastic tissue epileptogenicity, as demonstrated by intrale sional rhythmic spike discharges, the onset of ictal discharges and a low e pileptogenic threshold, The epileptogenic zone corresponded to histological ly defined FCD in 82% of the cases, Despite the lack of adequate neuroimagi ng in most cases, 64% of the patients became seizure-free after surgery, Th e main predictors of a favourable outcome were complete removal of the epil eptogenic zone (P < 0.01) and complete removal of the dysplastic cortex (P < 0.01). These results emphasize the usefulness of neurophysiological data in accurately assessing the extent of the FCD.