SECONDARY EPILEPTIC FOCI IN CHILDREN WITH INTRACTABLE EPILEPSY SECONDARY TO CORTICAL DYSPLASIAS

Objectives: Cortical dysplasias are intrinsically epileptogenic. Long and intractable seizure histories in childhood secondary to the cortical dysplasia provoke secondary epileptic foci. We evaluated spatial and temporal profiles and identify risk factors of secondary epileptogenesis Methods: We retrospectively studied 34 children with intractable localization-related epilepsy with histopathological confirmed cortical dysplasia. We reviewed seizure histories and semiologies, MR images, serial EEGs, video EEGs (VEEGs) and MEG findings. We defined secondary epileptic foci as new ictal onsets, remote and independent interictal discharges on subsequent EEGs, and new dipole locations on subsequent MEGs. We evaluated demographic variables, histopathology and secondary epileptic foci correlating with surgical outcomes according to Engel.

Results: We found secondary epileptic foci in 25 (74%) of 34 patients. They had new ictal onsets on VEEG in 5 (15%), secondary epileptic interictal discharges in 16 (47%), secondary clustered MEG dipoles in 5 (15%) scattered MEG dipoles in 17(50%). Fifteen (60%) of 25 patients with secondary epileptic foci and 4 (45%) of 9 patients without secondary epileptic foci became seizure free, Engel Ia. There was no significant difference in seizure outcome between the 2 groups of patients with/without secondary epileptic foci.

Conclusion: Secondary epileptic foci on VEEG and/or MEG did not necessarily correlate with a poor surgical outcome in patients with intractable localization-related epilepsy due to cortical dysplasias. Remaining seizures may be attributed to the residual epileptogenic zone around the resection area rather than secondary epileptic foci.