Temporal lobe seizures are accompanied by complex behavioral phenomena including loss of consciousness, dystonic movements and neuroendocrine changes. These phenomena may arise from extended neural networks beyond the temporal lobe. To investigate this, we imaged cerebral blood flow (CBF) changes during human temporal lobe seizures with single photon emission computed tomography (SPECT) while performing continuous video/EEG monitoring. We found that temporal lobe seizures associated with loss of consciousness produced CBF increases in the temporal lobe, followed by increases in bilateral midline subcortical structures. These changes were accompanied by marked bilateral CBF decreases in the frontal and parietal association cortex. In contrast, temporal lobe seizures in which consciousness was spared were not accompanied by these widespread CBF changes. The CBF decreases in frontal and parietal association cortex were strongly correlated with increases in midline structures such as the mediodorsal thalamus. These results suggest that impaired consciousness in temporal lobe seizures may result from focal abnormal activity in temporal and subcortical networks linked to widespread impaired function of the association cortex.

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Summary:Purpose: Statistical parametric mapping (SPM) is an image-analysis tool that assesses the statistical significance of cerebral blood flow (CBF) changes on a voxel-by-voxel basis, thereby removing the subjectivity inherent in conventional region-of-interest (ROI) analysis. Our platform of single-photon emission computed tomography (SPECT) ictalinterictal difference imaging in clinical epilepsy has been validated for localizing seizure onset. We extend the tools of SPM by further applying statistical measures for the significance of perfusion changes in individual patients to localize epileptogenic foci in patients with defined temporal lobe epilepsy by using paired scans in this preliminary study.Methods: Twelve patients with pairs of periictal and interictal SPECT scans were analyzed in this comparison study between SPECT difference imaging and SPM difference analysis by using a reference database of paired normal healthy images. These 12 patients possessed seizure foci localized to the mesial temporal lobe as confirmed by surgical outcome and by hippocampal sclerosis on pathology. SPM was used to identify clusters of increased or decreased CBF in each patient in contrast to our control group. Results:The regions having the most significant increased or decreased CBF by SPM analysis were in agreement with regions identified by conventional difference imaging and visual analysis by viewers blinded to the results of the SPM analysis. Differentiated further by time of radiopharmaceutical injection, six of seven patients injected within 100 s of seizure onset displayed hyperperfusion changes localized to the corresponding epileptogenic temporal lobe by both techniques. Among patients receiving injections after 100 s, both techniques showed primarily regions of hypoperfusion, which again were similar between these two methods.Conclusions: The results provide strong evidence supporting SPM difference analysis in assessing regions of significant CBF change from baseline in concordance with our current clinically used technique of SPECT ictal-interictal difference imaging in epilepsy patients. Difference analysis using SPM could serve as a useful diagnostic tool in the evaluation of seizure focus in temporal lobe epilepsy. Key Words: Epilepsy-Periictal SPECT-CBF difference imaging-Statistical parametric mapping (SPM).Single-photon emission computed tomography (SPECT) provides important clinical information measuring regional cerebral blood flow changes in the evaluation of epileptic seizure foci. In general, SPECT has demonstrated hyperperfusion in the epileptogenic region periictally and hypoperfusion interictally. Zubal et al. (1) demonstrated improved localization using SPECT difference imaging, whereby interictal images are subtracted on a voxel-by-voxel basis following co-registration and normalization with ictal images. However, the limitation of this approach as with most others remains its degree of interobserver variability (1-3). Other methods of SPECT interpretation have increased diagnostic yield. Ca...