Quantitative brain surface mapping of an electrophysiologic/metabolic mismatch in human neocortical epilepsy

Abstract

Summary The spatial relationship between an intracranial EEG-defined epileptic focus and cortical hypometabolism on glucose PET has not been precisely described. In order to quantitatively evaluate the hypothesis that ictal seizure onset and/or rapid seizure propagation, detected by subdural EEG monitoring, commonly involves normometabolic cortex adjacent to hypometabolic cortical regions, we applied a novel, landmark-constrained conformal mapping approach in 14 children with refractory neocortical epilepsy. The 3D brain surface was parcellated into finite cortical elements (FCEs), and hypometabolism was defined using lobe- and side-specific asymmetry indices derived from normal adult controls. The severity and location of hypometabolic areas vs. ictal intracranial EEG abnormalities were compared on the 3D brain surface. Hypometabolism was more severe in the seizure onset zone than in cortical areas covered by non-onset electrodes. However, similar proportions of the onset electrodes were located over and adjacent to (within 2 cm) hypometabolic regions (46% vs. 41%, respectively), whereas rapid seizure spread electrodes preferred these “adjacent areas” rather than the hypometabolic area itself (51% vs. 22%). On average, 58% of the hypometabolic regions had no early seizure involvement. These findings strongly support that the seizure onset zone often extends from hypometabolic to adjacent normometabolic cortex, while large portions of hypometabolic cortex are not involved in seizure onset or early propagation. The clinical utility of FDG PET in guiding subdural electrode placement in neocortical epilepsy could be greatly enhanced by extending grid coverage to at least 2 cm beyond hypometabolic cortex, when feasible.

fMRI language dominance and FDG-PET hypometabolism

“…4,5,12 Neocortical foci may be associated with hypometabolism that extends beyond the margin of the seizure focus. 13 In our study, only one patient with atypical language and normal MRI had normal FDG-PET. There are both structural and PET data to suggest perturbation of a more widespread network involving basal ganglia and frontal cortex.…”

Evaluating signal-correlated noise as a control task with language-related gamma activity on electrocorticography

“…Planar X-ray images (lateral and antero-posterior) were acquired with subdural electrodes in place for localization on the brain surface; three metallic fiducial markers at anatomically well-defined locations aided coregistration with MRI. A three-dimensional MRI brain surface image was created with electrode sites delineated (Alkonyi et al, 2009, Muzik et al, 2007, von Stockhausen et al, 1997). Accuracy was confirmed by intraoperative digital photographs showing in situ electrode locations (Asano et al, 2005, Nagasawa et al, 2010a, Wu et al, 2011).…”

Electrocorticographic correlates of overt articulation of 44 English phonemes: Intracranial recording in children with focal epilepsy

“…For ECoG recording, platinum grid and strip electrodes (10 mm intercontact distance, 4 mm diameter) were surgically implanted (Asano et al, 2009; Figures 1 and 2), and the location of each subdural electrode was co-registered to each individual’s three-dimensional surface MR image (Alkonyi et al, 2009; Muzik et al, 2007; von Stockhausen et al, 1997). Extraoperative video-ECoG recordings were obtained using a 192-channel Nihon Kohden Neurofax 1100A Digital System (Nihon Kohden America Inc, Foothill Ranch, CA, USA).…”