Abstracts

We wished to investigate the clinical characteristics and surgical outcomes in patients with hippocampal sclerosis whose scalp ictal EEG recordings localize to the opposite temporal lobe.
We retrospectively reviewed the data of all adult patients who had undergone depth electrode implantation at UCLA (1991-2001) or the Montreal Neurologic Institute (1991-1998) to identify patients who had a) unilateral hippocampal atrophy; and b) surface ictal recordings in which the majority of seizures appeared to initiate in the opposite temporal lobe, with few or none which were concordant with the hippocampal atrophy.
Of 109 patients who underwent depth electrode study at the two centers, there were 6 patients who met the aforementioned criteria. Five of these six had very severe hippocampal atrophy, while the sixth had mild atrophy but severe and extensive signal change on MR imaging. Depth electrode recordings in 5 of the 6 patients yielded clear ictal onset in the mesial temporal lobe ipsilateral to the imaging abnormality (contralateral to apparent scalp ictal onset). One patient had an unusual bitemporal onset pattern which was nonetheless suggestive of onset in the sclerotic hippocampus. No patient had intracranial ictal onset contralateral to the imaging abnormailty. All patients underwent resection of the structurally abnormal temporal lobe. After follow-up of at least 2 years 4 of 6 patients (67%) were completely free of disabling seizures, while the other two showed lesser degrees of improvement (Class II or III).
Some patients with severe hippocampal sclerosis (a [ldquo]burnt-out hippocampus[rdquo]) have rapid contralateral spread of ictal discharges, resulting in apparent gross discordance between imaging and scalp ictal recordings. These patients nonetheless have very good surgical outcomes on the whole. Whether or not such patients may forgo intracranial recordings requires further study.