False lateralization of electrographic onset in the setting of cerebral atrophy.

The localization of seizure onset relies on the concordance of clinical, electrographic, and imaging data, often supplemented by corroborating functional studies. On occasion, the presurgical evaluation may yield discordant information. Although the localization of seizure onset is sometimes in doubt, it is rare that the lateralization of the focus is in question. To date, there has been only a single publication on falsely lateralizing ictal EEG onsets in the setting of atrophic lesions. We describe two patients in whom the ictal EEG suggested seizure onset from the hemisphere opposite to the one with a sizeable atrophic lesion. The first patient was operated on without invasive EEG testing. In the second patient, we decided to place subdural electrodes before resection. In each case, resection of the lesion resulted in improvement of intractable seizures.