EPILEPSY SURGERY FOR NEONATAL OR INFANTILE ONSET SEIZURES: USE OF PET SCANNING

Abstract

Intractable epilepsy in infants and young children may lead to an epileptic encephalopathy. In such cases, epilepsy surgery should be considered. Surgical results are best when there is concordance between EEG localization and neuroimaging. PET scanning using 2-deoxy-2(18F)fluoro-D-glucose (FDG) identifies epileptic foci when MRI is non-revealing, and when a lesion is present, PET complements MRI by defining the full extent of the lesion and evaluating the integrity of surrounding brain regions. PET abnormalities may guide placement of intracranial electrodes, thus minimizing sampling errors. The size of the hypometabolic zone increases with chronic epilepsy, suggesting dynamic changes in the epileptic network. In infantile spasms, resection of focal PET abnormalities corresponding to focal EEG abnormalities is associated with improved seizure/cognitive outcome. Only about 20% of patients with 'cryptogenic infantile spasms' show a single PET focus amenable to resection. The majority shows multifocal hypometabolism and are not optimal surgical candidates. Bilateral symmetric hypometabolism suggests a nonlesional etiology, more consistent with neurogenetic/neurometabolic disorders. In infants with hemimegalencephaly, the relative integrity of the contralateral hemisphere is assessed using PET for prognostic purposes. In patients with Sturge-Weber syndrome, rapid demise of the affected hemisphere is associated with better seizure/cognitive outcome than slower progression because of brain plasticity. Other PET tracers may provide more specific assessment of seizure foci. 11C-flumazenil (FMZ) labels central benzodiazepine receptors, showing: decreased receptor binding in medial temporal sclerosis, perilesional epileptogenic zones, seizure onset zones, and secondary epileptic foci. 11C-alpha-methyl-L-tryptophan (AMT), an analogue of tryptophan, traces serotonin synthesis and kynurenine pathways and shows increased uptake in epileptogenic cortex interictally. In children with tuberous sclerosis, increased AMT uptake is seen around epileptogenic tubers, but not nonepileptogenic tubers. The list of PET tracers for epilepsy continues to grow and will eventually pinpoint precisely the cortical regions that should be resected to achieve best postoperative outcome.