Usefulness of 18FDG-PET in epilepsy. Methods and indications

Positron emission tomography (PET) using 18-fluorodeoxyglucose (18FDG) is currently used in pre surgical work-up for drug-resistant partial epilepsies in children as in adults, in addition to MRI. Recent cameras with less than 5 mm spatial resolution allow to obtain thin slices (about 2 mm thickness) in 3D planes. 18FDG is intravenously injected at the mean dose of 3 MBq/kg of body weight in inter-ictal and resting state, in a quiet, dimly lit environment and careful monitoring for head movements and ictal events. In children, sedation may be necessary. Image acquisition starts 30 min after injection and ended 15 to 20 min later. Semiquantitative analysis is visually assessed in clinical practice using colour scales. PET sensibility is improved by superimposition of metabolic imaging on MRI. Statistical analysis with S.P.M. may be useful but comparison with health subjects database is required. In medial temporal lobe epilepsy associated with hippocampal sclerosis, hypo metabolism ipsilateral to the epileptogenic focus is found in 70 to 90% of the cases and is predictive of surgical outcome. In other types of temporal and extra temporal epilepsy with negative MRI, focal hypo metabolism can be detected, allowing identification of minor gyral abnormalities corresponding to focal cortical dysplasia. In such MRI negative cases, PET findings may improve surgical outcome. (author)