Abstracts

RATIONALE: The goal of this study was to determine the ability of 1H MRSI to predict surgical outcome in patients with MRI-negative medically refractory temporal lobe epilepsy (TLE). TLE patients with concordant evidence of MTS on MRI have a high probability (>90%) of becoming seizure free following temporal lobectomy; however, only 50% of patients with normal MRIs become seizure free following surgery. At present there are no good predictors of surgical outcome for this group. METHODS: 1H MRSI obtained preoperatively from 13 patients with MRI negative TLE and seizure surgery with at least a one year follow-up were reviewed. All patients had an extensive pre-surgical evaluation and demonstrated well localized, unilateral temporal epileptogenic foci. 1H MRSI was performed using a 1.5T Siemens Vision system. The hippocampal spectra were analyzed in a blinded manner as previously described and the results were not used in the surgical planning. Because this patient population spanned two previous published series standardized Z-scores were compared. RESULTS: As previously reported, the NAA ratios were significantly reduced in the ipsilateral hippocampi whether compared to the contralateral side or to controls. The contralateral hippocampal NAA ratios were significantly decreased predominantly in those patients with non-seizure free outcomes (mean Z-scores, Class I 0.12 v Class II-IV -1.65, p<0.02 2-tailed Student t-test). 7 of the 13 MRI negative TLE patients had an Engel class I outcome with 4 of the 7 having contralateral hippocampal NAA ratios greater than the control mean (i.e. Z-score greater than zero); whereas, all 6 of the non-seizure free patients had Z-scores less than zero. Similarly, the ipsilateral hippocampi tended to be more severely affected in the non-seizure free group (mean Z-scores, Class I -0.73 v Class II-IV -2.66, p<0.03 2-tailed Student t-test). CONCLUSIONS: These preliminary findings suggest 1H MRSI can predict the surgical outcome in TLE patients without evidence of MTS on MRI. Patients with non-seizure free outcomes had bilaterally abnormal hippocampi including more severely involved ipsilateral hippocampi. (Supported by NIH Grant R01-NS31966)