[Functional imaging (PET and SPECT) in epilepsy]

Epilepsy is one of the most prevalent neurologic disorders and affects approximately 1% of the population. Most complex seizures arise from the temporal lobes and the condition of 20-30% of these patients is refractory to medication. Many can be rendered seizure free with surgery. Epilepsy surgery requires accurate identification of the site and extent of the epileptogenic area responsible for seizures. EEG is accepted as a gold standard, however only 50% of the patients are safely diagnosed. The need for invasive monitoring with possible hemorrhage or infection has been greatly reduced by the introduction of new technologies such as PET, SPECT and MRI in the clinical practice. MRI demonstrate morphologic changes in approximately 80% of patients with epilepsy. However, structural lesions may not always correlate with clinical, EEG and pathologic localization of epileptogenic foci. Seizures are associated with pronounced changes in regional cerebral blood flow. The real power of SPECT lies in the opportunity of ictal examinations, with a sensitivity ranging from 90 to 97%. Interictal PET studies using 18F-FDG measure regional glucose metabolism, have been investigated for their value as non-invasive focus-localizing techniques. These studies have sensitivity ranging from 80 to 85%. The benzodiazepine binding site that are associated with and modulate the activity of GABA receptors have been imaged by SPECT (using 123I-iomazenil) and PET (using 11C-Flumazenil). Combined measurements of benzodiazepine binding sites and perfusion/metabolism provide a more accurate visualization of epileptogenic site than perfusion or metabolism measurements alone. Functional imaging modalities (PET and SPECT) are highly important in the presurgical evaluation of patients with medically refractory complex partial seizures.