LATERALIZATION OF TEMPORAL-LOBE EPILEPSY BASED ON REGIONAL METABOLIC ABNORMALITIES IN PROTON MAGNETIC-RESONANCE SPECTROSCOPIC IMAGES

Magnetic resonance spectroscopic imaging (MRSI) is capable of determin ing the spatial distribution in vivo of cerebral metabolites, includin g N-acetylaspartate (NAA), a compound found only in neurons. We used t his technique in 10 patients with temporal lobe epilepsy (TLE) to dete rmine the location of maximal neuronal/axonal loss or damage and to ev aluate the potential of MRSI for presurgical lateralization. Asymmetry of the relative resonance intensity of NAA to creatine was determined for mid and posterior regions of the temporal lobes defined anatomica lly and also for ''metabolic lesions'' defined as the regions of maxim al abnormality on MRSI. MRSI revealed decreased relative signal intens ity in at least one temporal lobe of all patients. Two patients had a widespread reduction in NAA in both temporal lobes. The region of maxi mal abnormality was usually in the posterior temporal lobe but sometim es in the mid temporal lobe. The side of lowest NAA was ipsilateral to the clinical electroencephalographic lateralization in all patients. Lateralization based on NAA to creatine correlated with the atrophy of amygdala and hippocampus in 8 patients who showed this on magnetic re sonance imaging volumetric measurements. MRSI can demonstrate regional neuronal loss or damage that correlates with clinical electroencephal ographic and structural lateralization in temporal lobe epilepsy. The ability to identify a region of maximal metabolic abnormality on spect roscopic images may confer greater sensitivity than that available fro m single voxel methods. The maximal metabolic abnormality may not be l ocated in a voxel defined a priori, and based on anatomical considerat ions, without knowledge of the distribution of the metabolic abnormali ty.