Abstracts

The networks involved during seizure activity are not clearly known. Specifically in humans, spontaneous seizures that secondarily generalize have not been extensively studied. Using single photon emission computed tomography (SPECT) we looked at changes in cerebral blood flow (CBF) in patients with partial seizures that secondarily generalized. We analyzed a total of 51 patients (30 male 21 female; average age 33 years). Nineteen of the 51 patients were injected ictally and the remaining 32 post ictally, using Tc-99 HMPAO radiotracer. For each patient, an ictal scan was compared with a corresponding interictal scan using Ictal-interictal SPECT analyzed by SPM (ISAS; see http://spect.yale.edu/). Video behavioral and EEG changes were reviewed independently of the neuroimaging. We found that spontaneous generalized seizures have focal areas of CBF increases and decreases. When the radiotracer was injected before secondary generalization (n=10), during the partial phase, the region of greatest CBF increases correctly localized to seizure onset. These results were confirmed by a seizure free surgical outcome or in patients without surgery, a concordance of EEG, MRI, and clinical data. For injections during the generalized tonic-clonic (n=9) or postictal (n=32) phase, localization of onset was less predictable. Group analyses of CBF changes during the ictal periods revealed no consistent pattern. Group analyses in the postictal period revealed marked CBF increases in the cerebellum (p[lt]0.0001, Z=4.45), which appear initially in the vermis and later progress laterally to the cerebellar hemispheres. The orbitofrontal cortex, cingulate cortex and right parietal regions, demonstrated CBF decreases (p[lt]0.0001, Z=5.47) in a group analysis of postictal patients. Patients injected during the postictal period were in a deeply unresponsive state. Generalized tonic-clonic seizures involve focal regions and do not involve the entire brain homogenously. Early radiotracer injections before seizures are in the generalization phase are critical for accurate localization of seizure onset. Postictal increases in the cerebellar areas may reflect the neuronal activity involved in generalization. Postictal decreases in the orbitofrontal, cingulate and right parietal cortex may have implications for mechanisms of postictal impaired consciousness. (Supported by Blattmachr Fund.)