Abstracts

Rationale: Ictal single photon emission computed tomography (SPECT) is one of the diagnostic methods used to localize the seizure onset zone in children with focal epilepsy as part of the presurgical evaluation. This study is aimed to analyze the role of SPECT and timing of injection of radiotracer to localize the epileptogenic zone in children with refractory focal epilepsy.Methods: Thirty patients that were diagnosed with medically refractory focal epilepsy had their charts reviewed to obtain clinical information. These patients all underwent presurgical evaluation to identify the epileptogenic zone. Evaluation included FDG-PET, interictal and ictal SPECT scan, high resolution MRI and EEG video monitoring. Computerized analysis was performed to substract ictal and interictal SPECT data using statistical parametric mapping (SPM) (ISAS).Results: Mean age of seizure onset was 4.3 +/- 3.6 years (age: 0-13) and age at the time of evaluation was 11.8 +/- 4.8 years (age: 2-19). Epilepsy diagnosis was identified with a single epileptogenic focus in 14 and more than two foci in 16 patients. Based on the ictal EEG findings, epileptogenic focus was lateralized to the left (n:11), right (n:16) or bilateral hemispheres (n:3). Epileptogenic focus was localized to the frontal lobe in 11, temporal lobe in 9 and other locations in 10 patients. PET imaging was performed in 21 patients and focal hypometabolism was identified in 11 patients. All of the patients had brain MRI which was non-localizing in 14/30 (47%). Ictal SPECT was performed in 27 patients which localized the seizure onset zone in 19 (63%). The timing of the radiotracer injection was 13-/+9.6 (2-38 seconds). Sixteen patients received the ictal SPECT injection within the first 10 seconds (n:16, 59%), 7(26%) within 11-20 seconds, and 4 (15%) later than 20 seconds of ictal onset. Seizure focus was identified in 11 patients with ictal SPECT imaging who had non-localizing MRI findings. Earlier ictal SPECT injection (<20 seconds of the seizure onset) localized the ictal onset zone in 18 patients (18, 67%) so almost all patients who had ictal onset zone were identified by SPECT scan (n: 18/19). ISAS was performed in 14 patients which localized the ictal onset zone to the ipsilateral hemisphere in 10, contralateral hemisphere in 1 patient, and both hemispheres in 3 patients. In 6 patients who had non-localizing ictal SPECT data, subtraction analysis revealed the location of ictal onset zone. Twenty-three underwent surgery in our center and 14 (61%) had Engel class I and II outcome.Conclusions: This study further demonstrates the long delay between seizure onset and the timing of epilepsy surgery evaluation in children with focal epilepsy. In the presence of normal anatomical imaging, ictal SPECT scan has higher yield to identify seizure onset zone. Earlier injection of tracer has an important role in identifying the ictal onset zone, and application of subtraction analysis for ictal-interictal SPECT data will also help with identification of the ictal onset zone when there are non-localizing ictal SPECT results.