Prognostic value of proton magnetic resonance spectroscopic imaging for surgical outcome in patients with intractable temporal lobe epilepsy and bilateral hippocampal atrophy

The objective of this study was to assess which features of temporal lobe p roton magnetic resonance spectroscopic imaging (H-1-MRSI) are associated wi th satisfactory surgical outcome in patients with intractable temporal lobe epilepsy and bilateral hippocampal atrophy. We studied 21 patients with in tractable temporal lobe epilepsy and bilateral hippocampal atrophy defined by magnetic resonance imaging volumetric measurements who underwent surgica l treatment. H-1-MRSI was used to determine the relative resonance intensit y ratio of the neuronal marker N-acetylaspartate to creatine + phosphocreat ine (NAA/Cr) for mid and posterior temporal lobe regions of the left and ri ght hemisphere, as well as an asymmetry index. Values lower than 2 SDs bell ow the normal mean were considered abnormal. We used Engel's classification to assess surgical outcome with respect to seizure control. Eleven patient s (52%) were in class I-II and 10 (48%) were in class III-TV. All 21 were o perated on the side of maximal electroencephalographic (EEG) lateralization . Concordant lateralization of decreases in NAA/Cr to the side of surgery a nd normal NAA/Cr values in the contralateral posterior-temporal region were significantly associated with good surgical outcome: 11 (69%) of 16 patien ts with H-1-MRSI abnormalities concordant with EEG lateralization and none of the 5 patients with nonconcordant H-1-MRSI had a good outcome (class I-I I); 10 (77%) of 13 patients with normal NAA/Cr contralateral to the EEG lat eralization versus 1 (12.5%) of 8 of those with NAA/Cr reduction contralate ral to EEG lateralization were in class I-II. Regression correlation analys is showed significant linear correlation between the midtemporal NAA/Cr rel ative asymmetry ratio and surgical outcome; the greater the asymmetry, the better the outcome. We conclude that discriminant H-1-MRSI features associa ted with favorable surgical outcome in patients with temporal lobe epilepsy and bilateral hippocampal atrophy were (1) concordant H-1-MRSI lateralizat ion, (2) a greater side-to-side asymmetry off NAA/Cr, and (3) an absence of contralateral posterior NAA/Cr reduction.