USEFULNESS OF PROTON MR SPECTROSCOPY IN THE EVALUATION OF TEMPORAL-LOBE EPILEPSY

OBJECTIVE. The purpose of our study was to compare the ability of MR s pectroscopy with that of standard presurgical methods to accurately la teralize the abnormal hippocampus in a group of patients with complex partial seizures. SUBJECTS AND METHODS. Ten healthy volunteers (five m ale, five female) without a history of seizures, significant head trau ma, or other neurologic abnormalities were chosen to participate in th e study. Twelve consecutive patients (three male, nine female) having intractable temporal lobe epilepsy and undergoing presurgical evaluati on for temporal lobectomy were chosen to participate in the study. The condition of all patients was refractory to medications. All patients underwent presurgical examination with interictal and video ictal ele ctroencephalography, ictal single-photon emission computed tomography, interictal positron emission tomography, MR imaging, and neuropsychol ogic testing. When noninvasive data were inconclusive, depth or grid r ecordings were performed. The results of MR spectroscopy were also com pared with postsurgical seizure control as defined by the Engel classi fication. RESULTS. Nine (90%) of 10 control subjects showed no signifi cant difference in N-acetyl aspartate. One control subject showed 16% asymmetry in N-acetyl aspartate between sides. The control group showe d no statistically significant differences in ratios of N-acetyl aspar tate:creatine, N-acetyl aspartate:choline, or creatine:choline when co mparing sides (p < .05). All 12 patients showed clearly lateralizing v alues identified by the index of asymmetry in N-acetyl aspartate (rang e, 24-93%), with a mean difference of 51% (SD, 22) (p = .01). Addition ally, as a group, statistically significant indexes of asymmetry (p = .01) were seen in ratios of N-acetyl aspartate:choline (mean, 42; SD, 22%), N-acetyl aspartate:creatine (mean, 41; SD, 27), and N-acetyl asp artate:creatine + choline (mean, 42; SD, 22). Using an N-acetyl aspart ate index of asymmetry of greater than 15%, which represents the mean index of asymmetry of the control subjects +/- two SDs, as our cutoff level for lateralization, the correct side was identified in all patie nts. When comparing both hippocampi using an asymmetry index of 15% fo r N-acetyl aspartate:choline + creatine, 11 (92%) of 12 were correctly lateralized. When comparing the unaffected temporal lobes between pat ients and control subjects, no statistically significant differences w ere detected in any metabolites or ratios. CONCLUSION. Our study agree s with others in showing decreased N-acetyl aspartate in the hippocamp us of seizure patients when compared with control subjects. Using N-ac etyl aspartate, N-acetyl aspartate:creatine, N-acetyl aspartate:cholin e, and N-acetyl aspartate:creatine + choline as our parameters, patien ts with mesial temporal lobe epilepsy were correctly lateralized with MR spectroscopy when compared with clinical consensus criteria. We con sider MR spectroscopy to be complementary to MR imaging. Both studies can be performed as a single integrated examination.