Abstracts

An ictal single positron emission computerized tomographic (Spect) scan has come to represent a useful neuroimaging technique for seizure localization. The sensitivity of this data can be improved by combining it with a magnetic resonance image (MRI) of the brain in the format of subtraction ictal Spect coregistered to MRI (SISCOM). The purposes of this study are first, to determine how SISCOM data impacts surgical planning and outcome in patients with intractable epilepsy, and second to improve understanding of trans-synaptic activation (diaschisis) in patients with focal epilepsy.
To determine the impact of SISCOM data on surgical planning and outcome, we reviewed the SISCOM data of 72 patients with intractable epilepsy. The SISCOM data, along with data acquired during continuous video (surface-scalp) electroencephalography (EEG) and intracranial EEG recording, were reviewed and analyzed for concordance. The influence of this information on surgical planning was also studied. To elucidate the pathway of neuronal activity, the same SISCOM data were reviewed, in a blinded fashion, by 5 of the authors. Each scan was interpreted based on a primary and secondary focus, in addition to evidence of thalamic, brainstem, and/or cerebellar activity.
Of the 72 cases investigated for surgical treatment of epilepsy, SISCOM and EEG data were concordant in 55% of the cases. These patients either underwent surgery with a more confined intracranial electrode array, or were directed toward surgery without a phase II investigation. Of the 45% with discordant data, patients either underwent bilateral or broader unilateral electrode arrays, or were eliminated as surgical candidates. Decisions regarding electrode placement were based primarily on ictal EEG, secondarily on interictal EEG, and least of all on SISCOM data. With regard to trans-synaptic neuronal activity, there was evidence of cerebellar activation in 50%, thalamic activiation in 35%, and brainstem activation in 15%. Activation was ipsilateral to the presumed epileptic focus in nearly 60% and 75% of cases with cerebellar and thalamic activation, respectively.
Cases with discordance between EEG and SISCOM data are more likely to (a) be excluded from surgery, (b) have broader intracranial electrode arrays, and (c) undergo more conservative resection margins. SISCOM data has the least weight in surgical decision-making. Evidence of neuronal activation distant from the presumed epilepsy focus occurred in more than 50% of cases. The concept of neurophysiologic diaschisis may reflect pathways of augmented neuronal activity or recruitment, similar to neuronal plasticity, and may depend on the underlying pathology. The possibilities of a non-motoric role for the cerebellum in epilepsy, and a role for the thalamus in consciousness during an ictus are also discussed.
[Supported by: Internal funding (MCG).]