Effect of injection time on postictal SPET perfusion changes in medically refractory epilepsy

Single-photon emission tomography (SPET) brain imaging in epilepsy has beco me an increasingly important noninvasive tool in localizing the epileptogen ic site. Ictal SPET demonstrates the highest localization sensitivity as co mpared with postictal and interictal SPET. While ictal SPET consistently re veals hyperperfusion at the epileptogenic site, postictal SPET reveals eith er hyper- or hypoperfusion depending on the timing of radiopharmaceutical i njection. Much discussion in the literature exists about exactly when the t ransition from hyper- to hypoperfusion occurs at the epileptogenic site in postictal SPET The systematic examination of two clinical variables - time of injection from seizure onset and offset - was useful in understanding po stictal perfusion changes. Twenty-seven patients with medically refractory epilepsy receiving postictal and interictal SPET scans were studied. Quanti tative SPET difference imaging was used to evaluate perfusion changes in re lationship to injection time. Perfusion changes were found to reflect the t ime of injection in relation to seizure onset, but to be somewhat independe nt of seizure offset. Thus, the majority of patients (8/12, 67%) receiving postictal injections within 100 s after seizure onset demonstrated hyperper fusion, while all patients (15/15, 100%) receiving postictal injections mor e than 100 s after seizure onset showed hypoperfusion. The explanation of t his phenomenon is unknown but the findings appear to parallel known changes in cerebral lactate levels.