Abstracts

The usefulness of visual analysis of 18F-FDG PET images in cryptogenic intractable partial epilepsy remains discussed. MRI and 18F-FDG PET has dramatically improved since the last decade. We investigated 100 patients referred during the last 4 years for presurgical evaluation in order to assess the value of 18F-FDG PET when optimal MRI is normal. 49 women and 51 men were included (age range: 14-52 yrs old, mean: 29 yrs). Inclusion criteria were: normal high resolution MRI without any brain abnormalities, medically refractory epilepsy, candidate for surgery. All patients underwent presurgical evaluation including interictal and ictal EEG-video recordings, MRI and 18F-FDG PET examinations. Electroclinical diagnosis was temporal lobe epilepsy (TLE) in 63 patients and extra-temporal lobe epilepsy (ETLE) in 37 patients (including 22 patients with frontal lobe epilepsy). MRI was performed on a 1.5T device (GE medical system) with 3D T1 SPGR (124 axial sections), coronal T2 and FLAIR sequences. 18F-FDG-PET was performed on a high resolution head dedicated PET camera (953B ECAT Siemens: n=49, Exact HR+ Siemens n=51). Axial, coronal and sagittal PET images were visually assessed by two independent observers blinded to the electroclinical data. Inter-observer comparisons and concordance between PET and electro-clinical data were based on 1) presence or absence of hypometabolism, 2) localization and 3) lateralization of metabolic abnormalities. FDG-PET was abnormal in 82 % of patients with normal high-resolution MRI. Focal or regional hypometabolism was found in 86% of TLE and in 70% of ETLE. Metabolic and electro-clinical data were concordant in 87% of abnormal PET examinations. Inter-observer agreement was 86%. All discordant findings consisted on minor abnormalities considered as significant by one observer and as non significant by the other observer. This study demonstrates the very high reliability of visual analysis of 18F-FDG PET in patients with medically refractory partial epilepsy and normal MRI. This suggests that FDG PET should be systematically performed in all patients suffering from medically refractory partial epilepsy with a strictly normal MRI and candidates for surgery.