Abstracts

RATIONALE: To validate in children the ability of ictal SPECT to localize the epileptogenic zone(EZ)to be removed in comparison with the gold standards, intracranial EEG and surgical outcome.
METHODS: We compared the location of the areas of ictal increase of cerebral blood flow (CBF)on SPECT using ictal-interictal subtraction technique and that of the EZ determined by the intracranial EEG (18 cases) and postsurgery outcome in 21 children with refractory partial epilepsy and aged from 10 mths to 17 y (mean 6.5y). Eighteen had symptomatic epilepsy (12 focal cortical dysplasia, 4 dysembrioplastic neuroepithelial tumor), including 12 with extratemporal epilepsy. The tracer (99mTc-ECD) was injected under the control of video-EEG at a mean timelag of 18 seconds from seizure onset.
RESULTS: All patients had at least one area of hyperperfusion on ictal SPECT except one for whom the seizure had lasted less than 10 seconds. The area of maximal hyperperfusion on subtraction colocalized with the discharge in all 17 patients with intracranial EEG and with the EZ in 13 of them (76%).In the 4 remaining patients, maximal hyperperfusion showed the propagation but missed the EZ, not due to a delayed injection (mean 19 seconds)but to a rapid propagation or an infraclinical onset of the seizure. Additional areas of hyperpefusion at a lower intensity were also observed in ipsilateral basal ganglia and contralateral cerebellum in 13 cases. Ictal hypoperfused areas were found in 11 cases, but they involved areas distant from the EZ.
CONCLUSIONS: The area of maximum hyperperfusion determined by the subtraction of interictal and ictal SPECT scans is perfectly colocalized with the epileptogenic discharge and permits to identify the EZ in 3/4 of pediatric cases, provided the injection is performed very soon after seizure onset. Ictal SPECT provides therefore a remarkable non invasive tool to optimize the implantation of intracranial electrodes and to improve surgical outcome in childhood refractory epilepsy.