FDG-positron emission tomography and invasive EEG: seizure focus detection and surgical outcome

To study the value of [18F]2-deoxyglucose (FDG)-positron emission tomography when surface ictal EEG is nonlocalizing.

FDG-PET scans were performed in 46 patients with complex partial seizures (CPS) not localized by ictal surface-sphenoidal video-EEG (VEEG) telemetry. Interictal PET was performed with continuous EEG monitoring, and images were analyzed with a standard template. Forty patients subsequently had subdural and 6 had depth electrodes (invasive EEG, IEEG); 22 had bilateral implants. A focus was detected in 40, and 35 had temporal lobectomy based on IEEG localization.

There was a close association between IEEG and PET localization (p < 0.01): 26 patients had relative unilateral temporal FDG-PET hypometabolism, all had congruent IEEG, and 18 of 23 were seizure-free after temporal lobectomy. Five patients had unilateral frontotemporal hypometabolism (3 of 5 were seizure-free), 1 had frontal hypometabolism, and 14 had no lateralized PET abnormality (4 of 7 were seizure-free). Patients who became seizure-free had significantly higher lateral temporal asymmetry index (AI). PET showed > or = 15% relative temporal hypometabolism (AI) in 12 of 22 patients with nonlateralized surface ictal VEEG and was capable of distinguishing between frontal and temporal foci in 16 of 24 patients with lateralized, but not localized, surface ictal video-EEG.

FDG-PET provides valuable data in patients with unlocalized surface ictal EEG and can reduce the number of patients who require IEEG studies. Quantitation is necessary for optimal PET interpretation.