Disparity of perfusion and glucose metabolism of epileptogenic zones in temporal lobe epilepsy demonstrated by SPM/SPAM analysis on 15O water PET, [18F]FDG-PET, and [99mTc]-HMPAO SPECT

Purpose: To elucidate uncoupling of perfusion and metabolism and its significance in epilepsy, O-15 water and F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and Tc-99m hexamethyl-propyleneamine-oxime (HMPAO) single-photon emission computed tomography (SPELT) were examined by SPM (statistical parametric mapping) and quantitation by using SPAM (statistical probabilistic anatomic map). Methods: [O-15]water and [F-18]FDG-PET, and [Tc-99m]HMPAO SPELT were performed in 25 patients (SPELT in 17 of 25) with medial temporal lobe epilepsy. For volume of interest (VOI) count analysis, the normalized counts using VOI based on SPAM templates of PET and SPELT were compared with those of the normal controls. Perfusion or metabolism was found abnormal if the Z score was >2 for each VOL For SPM analysis, the differences between each patient's image and a group of normal control images (t statistic for p < 0.01) on a voxel-by-voxel basis were examined to find significant decreases in perfusion or metabolism. Results: With SPAM VOI count analysis, areas of hypoperfusion were found in 13 patients in the epileptogenic temporal lobes by [O-15]water PET and areas of hypometabolism in 21 patients by [F-18]FDG-PET. With voxel-based SPM analysis, the epileptogenic zones were localized in 15 by [O-15]water PET and in 23 patients by [F-18]FDG-PET. The localization by [O-15]water PET was concordant with that of [F-18]FDG-PET. The areas of hypoperfusion on [O-15]water PET were absent or smaller than the areas of hypometabolism on [F-18]FDG-PET. Interictal [Tc-99m]-HMPAO SPELT revealed the hypoperfused zones in seven of 17 patients on visual assessment. Conclusions: SPAM VOI count and SPM analysis of [O-15]water and [F-18]FDG-PET and [Tc-99m]-HMPAO SPELT revealed that in the same patients, the areas of hypoperfusion were concordant with but smaller than the areas of hypometabolism. Discordance of perfusion and metabolic abnormalities represents an uncoupling of perfusion and metabolism in the epileptogenic zones, and this might explain the lower diagnostic accuracy of perfusion imaging in temporal lobe epilepsy.