Abstracts

Rationale: In intractable neocortical epilepsy patients with normal magnetic resonance imaging (MRI), subtraction ictal single photon emission computed tomography (SPECT) co-registered to MRI or fluorine-18-fluorodeoxyglucose (FDG) positron emission tomography (PET)/MRI co-registration are techniques that were recently reported to improve detection of the epileptogenic region. By combining these methods, we hypothesize that subtraction ictal SPECT, FDG-PET and MRI image co-registration provides additional localizing information enhancing the detection of epileptogenic focus. Methods: We identified all patients with normal MRI who had interictal FDG-PET, an ictal and interictal SPECT during their presurgical evaluation between 2004 to 2009 and had undergone resective surgery and followed up for at least 6 months. Magnetization-prepared rapid-acquisition gradient-echo (MPRAGE) MRI, FDG-PET and SPECT images were co-registered using automated registration algorithm based on mutual information within SPM2. SPECT ictal-interictal difference image was created by subtracting the interictal SPECT image from the ictal image. This was then simultaneously displayed with FDG-PET and MPRAGE MRI sequence to identify congruent areas of hyperperfusion and hypometabolism . The area of resection and the region of MRI-PET-SPECT congruency were compared and the results were validated through seizure outcome analyses. Results: Twenty neocortical epilepsy patients (female n = 9; median 21 years; IQR: 9.3-29.5) were studied. All patients underwent invasive electroencephalography evaluation prior to surgical resection. Subtraction ictal SPECT, FDG-PET and MPRAGE MRI image co-registration allowed anatomic localization of concordant/discordant FDG-PET and SPECT abnormalities. Co-localized FDG-PET and SPECT abnormality was identified in 13 (65%) patients. Resection of the cortical area corresponding to the co-localized abnormality was strongly associated with a seizure-free outcome (p=0.017). Conclusions: The co-localization of PET/ictal SPECT abnormalities may enhance accurate detection of the epileptogenic region in the challenging group of patients with medically intractable neocortical epilepsy and normal MRI.