Abstracts

Cerebral blood flow (CBF) changes measured with single photon emission computed tomography (SPECT) can be helpful for localizing partial seizures. However, CBF changes during partial seizures with secondary generalization have not been thoroughly investigated. We sought to determine whether the whole brain is homogeneously involved in generalized tonic-clonic seizures (GTCS), or whether focal networks may be crucial. Investigation of brain regions involved may provide insight into the mechanisms of behavioral changes during GTCS. We identified 30 GTCS injected with Tc-99m HMPAO SPECT either during or immediately after seizures. Images were analyzed in SPM2 in comparison to interictal scans from the same patients. Also, in order to correlate the SPECT changes with behavioral changes, videos of each seizure were reviewed by 2 readers blinded to the imaging results, to classify and describe the different phases of the GTCS. We found that GTCS caused focal network activation on SPECT imaging, rather than involvement of the entire brain. Specifically, group analysis of all patients revealed that GTCS were associated with significant CBF increases in the cerebellum and decreases in the cingulate gyrus and orbitofrontal cortex. Interestingly, the changes in the cerebellum were time dependent during the postictal period: in patients injected during the early post-ictal period (0-60s after seizure end, mean injection time = 34.5s) cerebellar increases were confined to the superior vermis, whereas patients injected later ([gt]60s after seizure end, mean injection time = 135.9s) showed bilateral increases in the inferolateral cerebellar hemispheres. We found that the perfusion increases in the cerebellum may be related to the extent of the tonic phase. 8 of the 10 (80%) seizures with motionless tonic contraction were associated with significant cerebral blood flow increases in the cerebellum, whereas only 5 of the 20 (25%) seizures with less dramatic tonic motor activity had significant changes in the cerebellum. Cortical changes in other regions varied widely among patients, and did not correspond to the seizure localization identified by other data (EEG, MRI, and clinical information). GTCS are not truly generalized, rather specific networks are involved while others are relatively spared. These networks may explain some of the behavioral manifestations of GTCS. Cerebral blood flow increases in the cerebellum may be related to tonic activity. The functional significance of CBF decreases in the cingulate and orbitofrontal cortex during and following GTCS is not known. However, given the known role of these regions in attention, further investigations should determine whether these CBF decreases are related to impaired consciousness in GTCS. (Supported by Dana Foundation)