Summary:Purpose: Interictal measurements of cerebral blood flow are less helpful in localizing epileptic foci than are measurements of brain metabolism. This may be related to an uncoupling of blood flow and metabolism. In this study, brain metabolism and blood flow were compared in an acute experimental model of focal interictal epilepsy.Methods: Interictal epileptic foci were induced by an epicortical application of penicillin in rats. After 1 h, stereotyped interictal activity was initiated, lasting until the end of the experiment. Brain metabolism was determined with [ ''C]deoxyglucose, and cerebral blood flow with [ ''C]iodoantipyrine autoradiography.Results: In control experiments, metabolism and blood flow were coupled. In animals with focal interictal epileptic activity, the metabolism was strongly increased in the focus and reduced in areas lateral to the focus. In contralateral brain areas, blood flow and metabolism varied in a parallel fashion. Ipsilateral to the focus, however, blood flow and metabolism were altered disproportionately. In the focus, the increase of blood flow was less marked than the increase of metabolism, and the area with increased blood flow was larger than the area with increased metabolism. Lateral to the focus, in the area with a hypometabolism, blood flow was not concomitantly reduced.
Conclusions:The experiments show that blood flow and rnetabolism in focal epilepsy may be uncoupled in widespread regions. This is due neither to structural abnormalities nor to the duration or discharge pattern of epileptic activity. The results explain why interictal metabolic investigations have a higher predictive value in presurgical epilepsy evaluation than do interictal measurements of blood flow. Key Words: Epilepsy-Epileptic focus-Deoxyglucose-AutoradiographyHypometabolism-Blood flow-Iodoantipyrine-PenicillinInterictal-PET-SPECT.Patients with focal epilepsy refractory to treatment with antiepileptic drugs (AEDs) can often profit from surgery if the epileptic focus can be exactly delineated. With the advent of new functional imaging technologies, including positron emission tomography (PET) and single-photon-emission computed tomography (SPECT), invasive presurgical .epilepsy evaluation has become unnecessary in a growing number of patients. Interictal measurement of brain metabolism with deoxyglucose and PET has been reported to localize the epileptic focus in 70-90% of patients with complex partial seizures (1-11). This does not hold true for interictal blood flow measurements with SPECT and hexamethylpropylene amine oxime (HMPAO), or with PET and "0-labeling (10,(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). Blood-flow measurements do, however, contribute to focus localization when used as a marker of ictal epileptogenic activity (10,18,(22)(23)(24).Because blood flow and metabolism are usually assumed to be coupled (25)(26)(27), the discrepancy between Accepted April 9, 1998. Address correspondence and reprint requests to Dr. 0. W. Witte at Neurologische Klinik, Heinrich-Heine-Universita...