Evidence of neuronal injury outside the medial temporal lobe in temporal lobe epilepsy: N-acetylaspartate concentration reductions detected with multisection proton MR spectroscopic imaging--initial experience.

Abstract

To determine whether magnetic resonance (MR) spectroscopic imaging reveals metabolic changes, especially decreased N-acetylaspartate (NAA) concentrations outside the medial temporal lobe in patients with mesial temporal lobe epilepsy (TLE), consistent with neuropathologic findings of extratemporal neuronal impairment. Eleven patients with mesial TLE and 13 control subjects were examined with multisection MR spectroscopic imaging. Three MR spectroscopic imaging sections were acquired. Thirteen brain regions in each hemisphere and the midbrain were analyzed in each patient, and the NAA to creatine-phosphocreatine (Cr) plus choline-containing compounds (Ch) (NAA/[Cr + Ch]) ratios were determined. In addition, hemispheric and whole-brain values were calculated and statistically analyzed. The NAA/(Cr + Ch) ratio in the ipsilateral hippocampus was significantly reduced, compared with that in the contralateral hippocampus (P <.002) and compared with that in control subjects (P <.03), confirming findings in previous studies. In patients, whole-brain NAA/(Cr + Ch) ratio outside the hippocampus was significantly lower than that in control subjects (P <.002). For the ipsilateral hemisphere in patients, NAA/(Cr + Ch) ratio was significantly lower than that in control subjects (P <.0002). Comparisons between individual brain regions revealed trends toward lower NAA/(Cr + Ch) ratios in many areas of the ipsilateral and, to a lesser extent, the contralateral hemisphere outside the hippocampus and temporal lobe, suggesting diffuse impairment. Results suggest that repeated seizure activity damages neurons outside of the seizure focus.