Interictal hyperperfusion in seizure focus during days after ictus

Purpose: We retrospectively evaluated the temporal changes of the perfusion in seizure focus during days after ictus. Materials and Methods: Interictal 99mTc-ECD SPECT images obtained 1-14 days after ictal scan from 21 patients with intractable epilepsy (13 mesial temporal lobe epilepsy and 8 neocortical epilepsy) were analyzed. On ictal SPECT all patients had hyperperfusion in seizure foci that were successfully resected subsequently. No patient had an ictal event before interictal SPECT. In 4 patients, interictal FDG PET were performed within 1 day of interictal SPECT. Asymmetry indices of perfusion (pAI) and metabolism (mAI) between seizure focus and contralateral region ((ipsilateral-contralateral) / (ipsilateral + contralateral) x 200%) were calculated on interictal SPECT and PET images, respectively. Results: During 1-14 days after ictus, 57% of the patients had interictal hyperperfusion (pAI > 5%) in seizure foci. There was a significant inverse correlation between time interval after ictus and pAI (rho = -0.59, p < 0.01). The pAI became close to zero ∼4 days after ictus. Interictal FDG PET images obtained within 1 day of interictal SPECT from 4 patients who had interictal hyperperfusion (mean pAI = 7.2 ± 3.1%) revealed metabolic decrease in seizure foci (mean mAI = -36.3 ± 31.0%). Conclusion: We found interictal hyperperfusion in seizure focus during days after ictus in more than 50% of the patients. Thus one should be cautious when interpreting interictal scans obtained within several days after ictus. In addition, our results demonstrate a mismatch between perfusion and metabolism in seizure focus during days after ictus. This may, at least in part, explain a lower sensitivity of interictal SPECT for the localization of seizure focus than that of FDG PET